// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
+using System.Diagnostics;
+using System.Numerics;
using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics;
+using System.Runtime.Intrinsics.X86;
+using Internal.Runtime.CompilerServices;
+
+#if BIT64
+using nint = System.Int64;
+using nuint = System.UInt64;
+#else // BIT64
+using nint = System.Int32;
+using nuint = System.UInt32;
+#endif // BIT64
namespace System.Text
{
- /*
- * Contains naive unoptimized (non-SIMD) implementations of ASCII transcoding
- * operations. Vectorized methods can be substituted here as a drop-in replacement.
- */
-
- internal unsafe static class ASCIIUtility
+ internal static partial class ASCIIUtility
{
- [MethodImpl(MethodImplOptions.NoInlining)] // the actual implementation won't be inlined, so this shouldn't be either, lest it throw off benchmarks
- public static uint GetIndexOfFirstNonAsciiByte(byte* pBytes, uint byteCount)
+ /// <summary>
+ /// Returns <see langword="true"/> iff all bytes in <paramref name="value"/> are ASCII.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static bool AllBytesInUInt32AreAscii(uint value)
+ {
+ return ((value & 0x80808080u) == 0);
+ }
+
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static bool AllBytesInUInt64AreAscii(ulong value)
+ {
+ return ((value & 0x80808080_80808080ul) == 0);
+ }
+
+ /// <summary>
+ /// Returns <see langword="true"/> iff all chars in <paramref name="value"/> are ASCII.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static bool AllCharsInUInt32AreAscii(uint value)
+ {
+ return ((value & ~0x007F007Fu) == 0);
+ }
+
+ /// <summary>
+ /// Returns <see langword="true"/> iff all chars in <paramref name="value"/> are ASCII.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static bool AllCharsInUInt64AreAscii(ulong value)
+ {
+ return ((value & ~0x007F007F_007F007Ful) == 0);
+ }
+
+ /// <summary>
+ /// Given a 24-bit integer which represents a three-byte buffer read in machine endianness,
+ /// counts the number of consecutive ASCII bytes starting from the beginning of the buffer.
+ /// Returns a value 0 - 3, inclusive.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static uint CountNumberOfLeadingAsciiBytesFrom24BitInteger(uint value)
+ {
+ // This implementation seems to have better performance than tzcnt.
+
+ // The 'allBytesUpToNowAreAscii' DWORD uses bit twiddling to hold a 1 or a 0 depending
+ // on whether all processed bytes were ASCII. Then we accumulate all of the
+ // results to calculate how many consecutive ASCII bytes are present.
+
+ value = ~value;
+
+ if (BitConverter.IsLittleEndian)
+ {
+ // Read first byte
+ uint allBytesUpToNowAreAscii = (value >>= 7) & 1;
+ uint numAsciiBytes = allBytesUpToNowAreAscii;
+
+ // Read second byte
+ allBytesUpToNowAreAscii &= (value >>= 8);
+ numAsciiBytes += allBytesUpToNowAreAscii;
+
+ // Read third byte
+ allBytesUpToNowAreAscii &= (value >>= 8);
+ numAsciiBytes += allBytesUpToNowAreAscii;
+
+ return numAsciiBytes;
+ }
+ else
+ {
+ // Read first byte
+ uint allBytesUpToNowAreAscii = (value = ROL32(value, 1)) & 1;
+ uint numAsciiBytes = allBytesUpToNowAreAscii;
+
+ // Read second byte
+ allBytesUpToNowAreAscii &= (value = ROL32(value, 8));
+ numAsciiBytes += allBytesUpToNowAreAscii;
+
+ // Read third byte
+ allBytesUpToNowAreAscii &= (value = ROL32(value, 8));
+ numAsciiBytes += allBytesUpToNowAreAscii;
+
+ return numAsciiBytes;
+ }
+ }
+
+ /// <summary>
+ /// Given a DWORD which represents two packed chars in machine-endian order,
+ /// <see langword="true"/> iff the first char (in machine-endian order) is ASCII.
+ /// </summary>
+ /// <param name="value"></param>
+ /// <returns></returns>
+ private static bool FirstCharInUInt32IsAscii(uint value)
+ {
+ return (BitConverter.IsLittleEndian && (value & 0xFF80u) == 0)
+ || (!BitConverter.IsLittleEndian && (value & 0xFF800000u) == 0);
+ }
+
+ /// <summary>
+ /// Returns the index in <paramref name="pBuffer"/> where the first non-ASCII byte is found.
+ /// Returns <paramref name="bufferLength"/> if the buffer is empty or all-ASCII.
+ /// </summary>
+ /// <returns>An ASCII byte is defined as 0x00 - 0x7F, inclusive.</returns>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ public static unsafe nuint GetIndexOfFirstNonAsciiByte(byte* pBuffer, nuint bufferLength)
+ {
+ // If SSE2 is supported, use those specific intrinsics instead of the generic vectorized
+ // code below. This has two benefits: (a) we can take advantage of specific instructions like
+ // pmovmskb which we know are optimized, and (b) we can avoid downclocking the processor while
+ // this method is running.
+
+ return (Sse2.IsSupported)
+ ? GetIndexOfFirstNonAsciiByte_Sse2(pBuffer, bufferLength)
+ : GetIndexOfFirstNonAsciiByte_Default(pBuffer, bufferLength);
+ }
+
+ private static unsafe nuint GetIndexOfFirstNonAsciiByte_Default(byte* pBuffer, nuint bufferLength)
{
- uint idx = 0;
- for (; idx < byteCount; idx++)
+ // Squirrel away the original buffer reference. This method works by determining the exact
+ // byte reference where non-ASCII data begins, so we need this base value to perform the
+ // final subtraction at the end of the method to get the index into the original buffer.
+
+ byte* pOriginalBuffer = pBuffer;
+
+ // Before we drain off byte-by-byte, try a generic vectorized loop.
+ // Only run the loop if we have at least two vectors we can pull out.
+ // Note use of SBYTE instead of BYTE below; we're using the two's-complement
+ // representation of negative integers to act as a surrogate for "is ASCII?".
+
+ if (Vector.IsHardwareAccelerated && bufferLength >= 2 * (uint)Vector<sbyte>.Count)
+ {
+ uint SizeOfVectorInBytes = (uint)Vector<sbyte>.Count; // JIT will make this a const
+
+ if (Vector.GreaterThanOrEqualAll(Unsafe.ReadUnaligned<Vector<sbyte>>(pBuffer), Vector<sbyte>.Zero))
+ {
+ // The first several elements of the input buffer were ASCII. Bump up the pointer to the
+ // next aligned boundary, then perform aligned reads from here on out until we find non-ASCII
+ // data or we approach the end of the buffer. It's possible we'll reread data; this is ok.
+
+ byte* pFinalVectorReadPos = pBuffer + bufferLength - SizeOfVectorInBytes;
+ pBuffer = (byte*)(((nuint)pBuffer + SizeOfVectorInBytes) & ~(nuint)(SizeOfVectorInBytes - 1));
+
+#if DEBUG
+ long numBytesRead = pBuffer - pOriginalBuffer;
+ Debug.Assert(0 < numBytesRead && numBytesRead <= SizeOfVectorInBytes, "We should've made forward progress of at least one byte.");
+ Debug.Assert((nuint)numBytesRead <= bufferLength, "We shouldn't have read past the end of the input buffer.");
+#endif
+
+ Debug.Assert(pBuffer <= pFinalVectorReadPos, "Should be able to read at least one vector.");
+
+ do
+ {
+ Debug.Assert((nuint)pBuffer % SizeOfVectorInBytes == 0, "Vector read should be aligned.");
+ if (Vector.LessThanAny(Unsafe.Read<Vector<sbyte>>(pBuffer), Vector<sbyte>.Zero))
+ {
+ break; // found non-ASCII data
+ }
+
+ pBuffer += SizeOfVectorInBytes;
+ } while (pBuffer <= pFinalVectorReadPos);
+
+ // Adjust the remaining buffer length for the number of elements we just consumed.
+
+ bufferLength -= (nuint)pBuffer;
+ bufferLength += (nuint)pOriginalBuffer;
+ }
+ }
+
+ // At this point, the buffer length wasn't enough to perform a vectorized search, or we did perform
+ // a vectorized search and encountered non-ASCII data. In either case go down a non-vectorized code
+ // path to drain any remaining ASCII bytes.
+ //
+ // We're going to perform unaligned reads, so prefer 32-bit reads instead of 64-bit reads.
+ // This also allows us to perform more optimized bit twiddling tricks to count the number of ASCII bytes.
+
+ uint currentUInt32;
+
+ // Try reading 64 bits at a time in a loop.
+
+ for (; bufferLength >= 8; bufferLength -= 8)
+ {
+ currentUInt32 = Unsafe.ReadUnaligned<uint>(pBuffer);
+ uint nextUInt32 = Unsafe.ReadUnaligned<uint>(pBuffer + 4);
+
+ if (!AllBytesInUInt32AreAscii(currentUInt32 | nextUInt32))
+ {
+ // One of these two values contains non-ASCII bytes.
+ // Figure out which one it is, then put it in 'current' so that we can drain the ASCII bytes.
+
+ if (AllBytesInUInt32AreAscii(currentUInt32))
+ {
+ currentUInt32 = nextUInt32;
+ pBuffer += 4;
+ }
+
+ goto FoundNonAsciiData;
+ }
+
+ pBuffer += 8; // consumed 8 ASCII bytes
+ }
+
+ // From this point forward we don't need to update bufferLength.
+ // Try reading 32 bits.
+
+ if ((bufferLength & 4) != 0)
+ {
+ currentUInt32 = Unsafe.ReadUnaligned<uint>(pBuffer);
+ if (!AllBytesInUInt32AreAscii(currentUInt32))
+ {
+ goto FoundNonAsciiData;
+ }
+
+ pBuffer += 4;
+ }
+
+ // Try reading 16 bits.
+
+ if ((bufferLength & 2) != 0)
+ {
+ currentUInt32 = Unsafe.ReadUnaligned<ushort>(pBuffer);
+ if (!AllBytesInUInt32AreAscii(currentUInt32))
+ {
+ goto FoundNonAsciiData;
+ }
+
+ pBuffer += 2;
+ }
+
+ // Try reading 8 bits
+
+ if ((bufferLength & 1) != 0)
{
- if ((sbyte)pBytes[idx] < 0)
+ // If the buffer contains non-ASCII data, the comparison below will fail, and
+ // we'll end up not incrementing the buffer reference.
+
+ if (*(sbyte*)pBuffer >= 0)
{
- break;
+ pBuffer++;
}
}
- return idx;
+
+ Finish:
+
+ nuint totalNumBytesRead = (nuint)pBuffer - (nuint)pOriginalBuffer;
+ return totalNumBytesRead;
+
+ FoundNonAsciiData:
+
+ Debug.Assert(!AllBytesInUInt32AreAscii(currentUInt32), "Shouldn't have reached this point if we have an all-ASCII input.");
+
+ // The method being called doesn't bother looking at whether the high byte is ASCII. There are only
+ // two scenarios: (a) either one of the earlier bytes is not ASCII and the search terminates before
+ // we get to the high byte; or (b) all of the earlier bytes are ASCII, so the high byte must be
+ // non-ASCII. In both cases we only care about the low 24 bits.
+
+ pBuffer += CountNumberOfLeadingAsciiBytesFrom24BitInteger(currentUInt32);
+ goto Finish;
}
- [MethodImpl(MethodImplOptions.NoInlining)] // the actual implementation won't be inlined, so this shouldn't be either, lest it throw off benchmarks
- public static uint GetIndexOfFirstNonAsciiChar(char* pChars, uint charCount)
+ [MethodImpl(MethodImplOptions.AggressiveOptimization)]
+ private static unsafe nuint GetIndexOfFirstNonAsciiByte_Sse2(byte* pBuffer, nuint bufferLength)
{
- uint idx = 0;
- for (; idx < charCount; idx++)
+ // JIT turns the below into constants
+
+ uint SizeOfVector128 = (uint)Unsafe.SizeOf<Vector128<byte>>();
+ nuint MaskOfAllBitsInVector128 = (nuint)(SizeOfVector128 - 1);
+
+ Debug.Assert(Sse2.IsSupported, "Should've been checked by caller.");
+ Debug.Assert(BitConverter.IsLittleEndian, "SSE2 assumes little-endian.");
+
+ uint currentMask, secondMask;
+ byte* pOriginalBuffer = pBuffer;
+
+ // This method is written such that control generally flows top-to-bottom, avoiding
+ // jumps as much as possible in the optimistic case of a large enough buffer and
+ // "all ASCII". If we see non-ASCII data, we jump out of the hot paths to targets
+ // after all the main logic.
+
+ if (bufferLength < SizeOfVector128)
+ {
+ goto InputBufferLessThanOneVectorInLength; // can't vectorize; drain primitives instead
+ }
+
+ // Read the first vector unaligned.
+
+ currentMask = (uint)Sse2.MoveMask(Sse2.LoadVector128(pBuffer)); // unaligned load
+
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+
+ // If we have less than 32 bytes to process, just go straight to the final unaligned
+ // read. There's no need to mess with the loop logic in the middle of this method.
+
+ if (bufferLength < 2 * SizeOfVector128)
+ {
+ goto IncrementCurrentOffsetBeforeFinalUnalignedVectorRead;
+ }
+
+ // Now adjust the read pointer so that future reads are aligned.
+
+ pBuffer = (byte*)(((nuint)pBuffer + SizeOfVector128) & ~(nuint)MaskOfAllBitsInVector128);
+
+#if DEBUG
+ long numBytesRead = pBuffer - pOriginalBuffer;
+ Debug.Assert(0 < numBytesRead && numBytesRead <= SizeOfVector128, "We should've made forward progress of at least one byte.");
+ Debug.Assert((nuint)numBytesRead <= bufferLength, "We shouldn't have read past the end of the input buffer.");
+#endif
+
+ // Adjust the remaining length to account for what we just read.
+
+ bufferLength += (nuint)pOriginalBuffer;
+ bufferLength -= (nuint)pBuffer;
+
+ // The buffer is now properly aligned.
+ // Read 2 vectors at a time if possible.
+
+ if (bufferLength >= 2 * SizeOfVector128)
+ {
+ byte* pFinalVectorReadPos = (byte*)((nuint)pBuffer + bufferLength - 2 * SizeOfVector128);
+
+ // After this point, we no longer need to update the bufferLength value.
+
+ do
+ {
+ Vector128<byte> firstVector = Sse2.LoadAlignedVector128(pBuffer);
+ Vector128<byte> secondVector = Sse2.LoadAlignedVector128(pBuffer + SizeOfVector128);
+
+ currentMask = (uint)Sse2.MoveMask(firstVector);
+ secondMask = (uint)Sse2.MoveMask(secondVector);
+
+ if ((currentMask | secondMask) != 0)
+ {
+ goto FoundNonAsciiDataInInnerLoop;
+ }
+
+ pBuffer += 2 * SizeOfVector128;
+ } while (pBuffer <= pFinalVectorReadPos);
+ }
+
+ // We have somewhere between 0 and (2 * vector length) - 1 bytes remaining to read from.
+ // Since the above loop doesn't update bufferLength, we can't rely on its absolute value.
+ // But we _can_ rely on it to tell us how much remaining data must be drained by looking
+ // at what bits of it are set. This works because had we updated it within the loop above,
+ // we would've been adding 2 * SizeOfVector128 on each iteration, but we only care about
+ // bits which are less significant than those that the addition would've acted on.
+
+ // If there is fewer than one vector length remaining, skip the next aligned read.
+
+ if ((bufferLength & SizeOfVector128) == 0)
+ {
+ goto DoFinalUnalignedVectorRead;
+ }
+
+ // At least one full vector's worth of data remains, so we can safely read it.
+ // Remember, at this point pBuffer is still aligned.
+
+ currentMask = (uint)Sse2.MoveMask(Sse2.LoadAlignedVector128(pBuffer));
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+
+ IncrementCurrentOffsetBeforeFinalUnalignedVectorRead:
+
+ pBuffer += SizeOfVector128;
+
+ DoFinalUnalignedVectorRead:
+
+ if (((byte)bufferLength & MaskOfAllBitsInVector128) != 0)
+ {
+ // Perform an unaligned read of the last vector.
+ // We need to adjust the pointer because we're re-reading data.
+
+ pBuffer += (bufferLength & MaskOfAllBitsInVector128) - SizeOfVector128;
+
+ currentMask = (uint)Sse2.MoveMask(Sse2.LoadVector128(pBuffer)); // unaligned load
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+
+ pBuffer += SizeOfVector128;
+ }
+
+ Finish:
+
+ return (nuint)pBuffer - (nuint)pOriginalBuffer; // and we're done!
+
+ FoundNonAsciiDataInInnerLoop:
+
+ // If the current (first) mask isn't the mask that contains non-ASCII data, then it must
+ // instead be the second mask. If so, skip the entire first mask and drain ASCII bytes
+ // from the second mask.
+
+ if (currentMask == 0)
+ {
+ pBuffer += SizeOfVector128;
+ currentMask = secondMask;
+ }
+
+ FoundNonAsciiDataInCurrentMask:
+
+ // The mask contains - from the LSB - a 0 for each ASCII byte we saw, and a 1 for each non-ASCII byte.
+ // Tzcnt is the correct operation to count the number of zero bits quickly. If this instruction isn't
+ // available, we'll fall back to a normal loop.
+
+ Debug.Assert(currentMask != 0, "Shouldn't be here unless we see non-ASCII data.");
+ pBuffer += (uint)BitOperations.TrailingZeroCount(currentMask);
+
+ goto Finish;
+
+ FoundNonAsciiDataInCurrentDWord:
+
+ uint currentDWord;
+ Debug.Assert(!AllBytesInUInt32AreAscii(currentDWord), "Shouldn't be here unless we see non-ASCII data.");
+ pBuffer += CountNumberOfLeadingAsciiBytesFrom24BitInteger(currentDWord);
+
+ goto Finish;
+
+ InputBufferLessThanOneVectorInLength:
+
+ // These code paths get hit if the original input length was less than one vector in size.
+ // We can't perform vectorized reads at this point, so we'll fall back to reading primitives
+ // directly. Note that all of these reads are unaligned.
+
+ Debug.Assert(bufferLength < SizeOfVector128);
+
+ // QWORD drain
+
+ if ((bufferLength & 8) != 0)
+ {
+ if (Bmi1.X64.IsSupported)
+ {
+ // If we can use 64-bit tzcnt to count the number of leading ASCII bytes, prefer it.
+
+ ulong candidateUInt64 = Unsafe.ReadUnaligned<ulong>(pBuffer);
+ if (!AllBytesInUInt64AreAscii(candidateUInt64))
+ {
+ // Clear everything but the high bit of each byte, then tzcnt.
+ // Remember the / 8 at the end to convert bit count to byte count.
+
+ candidateUInt64 &= 0x80808080_80808080ul;
+ pBuffer += (nuint)(Bmi1.X64.TrailingZeroCount(candidateUInt64) / 8);
+ goto Finish;
+ }
+ }
+ else
+ {
+ // If we can't use 64-bit tzcnt, no worries. We'll just do 2x 32-bit reads instead.
+
+ currentDWord = Unsafe.ReadUnaligned<uint>(pBuffer);
+ uint nextDWord = Unsafe.ReadUnaligned<uint>(pBuffer + 4);
+
+ if (!AllBytesInUInt32AreAscii(currentDWord | nextDWord))
+ {
+ // At least one of the values wasn't all-ASCII.
+ // We need to figure out which one it was and stick it in the currentMask local.
+
+ if (AllBytesInUInt32AreAscii(currentDWord))
+ {
+ currentDWord = nextDWord; // this one is the culprit
+ pBuffer += 4;
+ }
+
+ goto FoundNonAsciiDataInCurrentDWord;
+ }
+ }
+
+ pBuffer += 8; // successfully consumed 8 ASCII bytes
+ }
+
+ // DWORD drain
+
+ if ((bufferLength & 4) != 0)
+ {
+ currentDWord = Unsafe.ReadUnaligned<uint>(pBuffer);
+
+ if (!AllBytesInUInt32AreAscii(currentDWord))
+ {
+ goto FoundNonAsciiDataInCurrentDWord;
+ }
+
+ pBuffer += 4; // successfully consumed 4 ASCII bytes
+ }
+
+ // WORD drain
+ // (We movzx to a DWORD for ease of manipulation.)
+
+ if ((bufferLength & 2) != 0)
+ {
+ currentDWord = Unsafe.ReadUnaligned<ushort>(pBuffer);
+
+ if (!AllBytesInUInt32AreAscii(currentDWord))
+ {
+ // We only care about the 0x0080 bit of the value. If it's not set, then we
+ // increment currentOffset by 1. If it's set, we don't increment it at all.
+
+ pBuffer += (nuint)((nint)(sbyte)currentDWord >> 7) + 1;
+ goto Finish;
+ }
+
+ pBuffer += 2; // successfully consumed 2 ASCII bytes
+ }
+
+ // BYTE drain
+
+ if ((bufferLength & 1) != 0)
{
- if (pChars[idx] > 0x7Fu)
+ // sbyte has non-negative value if byte is ASCII.
+
+ if (*(sbyte*)(pBuffer) >= 0)
{
- break;
+ pBuffer++; // successfully consumed a single byte
}
}
- return idx;
+
+ goto Finish;
+ }
+
+ /// <summary>
+ /// Returns the index in <paramref name="pBuffer"/> where the first non-ASCII char is found.
+ /// Returns <paramref name="bufferLength"/> if the buffer is empty or all-ASCII.
+ /// </summary>
+ /// <returns>An ASCII char is defined as 0x0000 - 0x007F, inclusive.</returns>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ public static unsafe nuint GetIndexOfFirstNonAsciiChar(char* pBuffer, nuint bufferLength /* in chars */)
+ {
+ // If SSE2 is supported, use those specific intrinsics instead of the generic vectorized
+ // code below. This has two benefits: (a) we can take advantage of specific instructions like
+ // pmovmskb which we know are optimized, and (b) we can avoid downclocking the processor while
+ // this method is running.
+
+ return (Sse2.IsSupported)
+ ? GetIndexOfFirstNonAsciiChar_Sse2(pBuffer, bufferLength)
+ : GetIndexOfFirstNonAsciiChar_Default(pBuffer, bufferLength);
}
- [MethodImpl(MethodImplOptions.NoInlining)] // the actual implementation won't be inlined, so this shouldn't be either, lest it throw off benchmarks
- public static uint NarrowUtf16ToAscii(char* pChars, byte* pBytes, uint elementCount)
+ private static unsafe nuint GetIndexOfFirstNonAsciiChar_Default(char* pBuffer, nuint bufferLength /* in chars */)
{
- uint idx = 0;
- for (; idx < elementCount; idx++)
+ // Squirrel away the original buffer reference.This method works by determining the exact
+ // char reference where non-ASCII data begins, so we need this base value to perform the
+ // final subtraction at the end of the method to get the index into the original buffer.
+
+ char* pOriginalBuffer = pBuffer;
+
+ Debug.Assert(bufferLength <= nuint.MaxValue / sizeof(char));
+
+ // Before we drain off char-by-char, try a generic vectorized loop.
+ // Only run the loop if we have at least two vectors we can pull out.
+
+ if (Vector.IsHardwareAccelerated && bufferLength >= 2 * (uint)Vector<ushort>.Count)
+ {
+ uint SizeOfVectorInChars = (uint)Vector<ushort>.Count; // JIT will make this a const
+ uint SizeOfVectorInBytes = (uint)Vector<byte>.Count; // JIT will make this a const
+
+ Vector<ushort> maxAscii = new Vector<ushort>(0x007F);
+
+ if (Vector.LessThanOrEqualAll(Unsafe.ReadUnaligned<Vector<ushort>>(pBuffer), maxAscii))
+ {
+ // The first several elements of the input buffer were ASCII. Bump up the pointer to the
+ // next aligned boundary, then perform aligned reads from here on out until we find non-ASCII
+ // data or we approach the end of the buffer. It's possible we'll reread data; this is ok.
+
+ char* pFinalVectorReadPos = pBuffer + bufferLength - SizeOfVectorInChars;
+ pBuffer = (char*)(((nuint)pBuffer + SizeOfVectorInBytes) & ~(nuint)(SizeOfVectorInBytes - 1));
+
+#if DEBUG
+ long numCharsRead = pBuffer - pOriginalBuffer;
+ Debug.Assert(0 < numCharsRead && numCharsRead <= SizeOfVectorInChars, "We should've made forward progress of at least one char.");
+ Debug.Assert((nuint)numCharsRead <= bufferLength, "We shouldn't have read past the end of the input buffer.");
+#endif
+
+ Debug.Assert(pBuffer <= pFinalVectorReadPos, "Should be able to read at least one vector.");
+
+ do
+ {
+ Debug.Assert((nuint)pBuffer % SizeOfVectorInChars == 0, "Vector read should be aligned.");
+ if (Vector.GreaterThanAny(Unsafe.Read<Vector<ushort>>(pBuffer), maxAscii))
+ {
+ break; // found non-ASCII data
+ }
+ pBuffer += SizeOfVectorInChars;
+ } while (pBuffer <= pFinalVectorReadPos);
+
+ // Adjust the remaining buffer length for the number of elements we just consumed.
+
+ bufferLength -= ((nuint)pBuffer - (nuint)pOriginalBuffer) / sizeof(char);
+ }
+ }
+
+ // At this point, the buffer length wasn't enough to perform a vectorized search, or we did perform
+ // a vectorized search and encountered non-ASCII data. In either case go down a non-vectorized code
+ // path to drain any remaining ASCII chars.
+ //
+ // We're going to perform unaligned reads, so prefer 32-bit reads instead of 64-bit reads.
+ // This also allows us to perform more optimized bit twiddling tricks to count the number of ASCII chars.
+
+ uint currentUInt32;
+
+ // Try reading 64 bits at a time in a loop.
+
+ for (; bufferLength >= 4; bufferLength -= 4) // 64 bits = 4 * 16-bit chars
+ {
+ currentUInt32 = Unsafe.ReadUnaligned<uint>(pBuffer);
+ uint nextUInt32 = Unsafe.ReadUnaligned<uint>(pBuffer + 4 / sizeof(char));
+
+ if (!AllCharsInUInt32AreAscii(currentUInt32 | nextUInt32))
+ {
+ // One of these two values contains non-ASCII chars.
+ // Figure out which one it is, then put it in 'current' so that we can drain the ASCII chars.
+
+ if (AllCharsInUInt32AreAscii(currentUInt32))
+ {
+ currentUInt32 = nextUInt32;
+ pBuffer += 2;
+ }
+
+ goto FoundNonAsciiData;
+ }
+
+ pBuffer += 4; // consumed 4 ASCII chars
+ }
+
+ // From this point forward we don't need to keep track of the remaining buffer length.
+ // Try reading 32 bits.
+
+ if ((bufferLength & 2) != 0) // 32 bits = 2 * 16-bit chars
+ {
+ currentUInt32 = Unsafe.ReadUnaligned<uint>(pBuffer);
+ if (!AllCharsInUInt32AreAscii(currentUInt32))
+ {
+ goto FoundNonAsciiData;
+ }
+
+ pBuffer += 2;
+ }
+
+ // Try reading 16 bits.
+ // No need to try an 8-bit read after this since we're working with chars.
+
+ if ((bufferLength & 1) != 0)
{
- uint ch = pChars[idx];
- if (ch > 0x7Fu)
+ // If the buffer contains non-ASCII data, the comparison below will fail, and
+ // we'll end up not incrementing the buffer reference.
+
+ if (*pBuffer <= 0x007F)
{
- break;
+ pBuffer++;
}
- pBytes[idx] = (byte)ch;
}
- return idx;
+
+ Finish:
+
+ nuint totalNumBytesRead = (nuint)pBuffer - (nuint)pOriginalBuffer;
+ Debug.Assert(totalNumBytesRead % sizeof(char) == 0, "Total number of bytes read should be even since we're working with chars.");
+ return totalNumBytesRead / sizeof(char); // convert byte count -> char count before returning
+
+ FoundNonAsciiData:
+
+ Debug.Assert(!AllCharsInUInt32AreAscii(currentUInt32), "Shouldn't have reached this point if we have an all-ASCII input.");
+
+ // We don't bother looking at the second char - only the first char.
+
+ if (FirstCharInUInt32IsAscii(currentUInt32))
+ {
+ pBuffer++;
+ }
+
+ goto Finish;
}
- [MethodImpl(MethodImplOptions.NoInlining)] // the actual implementation won't be inlined, so this shouldn't be either, lest it throw off benchmarks
- public static uint WidenAsciiToUtf16(byte* pBytes, char* pChars, uint elementCount)
+ [MethodImpl(MethodImplOptions.AggressiveOptimization)]
+ private static unsafe nuint GetIndexOfFirstNonAsciiChar_Sse2(char* pBuffer, nuint bufferLength /* in chars */)
{
- uint idx = 0;
- for (; idx < elementCount; idx++)
+ // This method contains logic optimized for both SSE2 and SSE41. Much of the logic in this method
+ // will be elided by JIT once we determine which specific ISAs we support.
+
+ // Quick check for empty inputs.
+
+ if (bufferLength == 0)
+ {
+ return 0;
+ }
+
+ // JIT turns the below into constants
+
+ uint SizeOfVector128InBytes = (uint)Unsafe.SizeOf<Vector128<byte>>();
+ uint SizeOfVector128InChars = SizeOfVector128InBytes / sizeof(char);
+
+ Debug.Assert(Sse2.IsSupported, "Should've been checked by caller.");
+ Debug.Assert(BitConverter.IsLittleEndian, "SSE2 assumes little-endian.");
+
+ Vector128<short> firstVector, secondVector;
+ uint currentMask;
+ char* pOriginalBuffer = pBuffer;
+
+ if (bufferLength < SizeOfVector128InChars)
{
- byte b = pBytes[idx];
- if (b > 0x7F)
+ goto InputBufferLessThanOneVectorInLength; // can't vectorize; drain primitives instead
+ }
+
+ // This method is written such that control generally flows top-to-bottom, avoiding
+ // jumps as much as possible in the optimistic case of "all ASCII". If we see non-ASCII
+ // data, we jump out of the hot paths to targets at the end of the method.
+
+ Vector128<short> asciiMaskForPTEST = Vector128.Create(unchecked((short)0xFF80)); // used for PTEST on supported hardware
+ Vector128<ushort> asciiMaskForPMINUW = Vector128.Create((ushort)0x0080); // used for PMINUW on supported hardware
+ Vector128<short> asciiMaskForPXOR = Vector128.Create(unchecked((short)0x8000)); // used for PXOR
+ Vector128<short> asciiMaskForPCMPGTW = Vector128.Create(unchecked((short)0x807F)); // used for PCMPGTW
+
+ Debug.Assert(bufferLength <= nuint.MaxValue / sizeof(char));
+
+ // Read the first vector unaligned.
+
+ firstVector = Sse2.LoadVector128((short*)pBuffer); // unaligned load
+
+ if (Sse41.IsSupported)
+ {
+ // The SSE41-optimized code path works by forcing the 0x0080 bit in each WORD of the vector to be
+ // set iff the WORD element has value >= 0x0080 (non-ASCII). Then we'll treat it as a BYTE vector
+ // in order to extract the mask.
+ currentMask = (uint)Sse2.MoveMask(Sse41.Min(firstVector.AsUInt16(), asciiMaskForPMINUW).AsByte());
+ }
+ else
+ {
+ // The SSE2-optimized code path works by forcing each WORD of the vector to be 0xFFFF iff the WORD
+ // element has value >= 0x0080 (non-ASCII). Then we'll treat it as a BYTE vector in order to extract
+ // the mask.
+ currentMask = (uint)Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(firstVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte());
+ }
+
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+
+ // If we have less than 32 bytes to process, just go straight to the final unaligned
+ // read. There's no need to mess with the loop logic in the middle of this method.
+
+ // Adjust the remaining length to account for what we just read.
+ // For the remainder of this code path, bufferLength will be in bytes, not chars.
+
+ bufferLength <<= 1; // chars to bytes
+
+ if (bufferLength < 2 * SizeOfVector128InBytes)
+ {
+ goto IncrementCurrentOffsetBeforeFinalUnalignedVectorRead;
+ }
+
+ // Now adjust the read pointer so that future reads are aligned.
+
+ pBuffer = (char*)(((nuint)pBuffer + SizeOfVector128InBytes) & ~(nuint)(SizeOfVector128InBytes - 1));
+
+#if DEBUG
+ long numCharsRead = pBuffer - pOriginalBuffer;
+ Debug.Assert(0 < numCharsRead && numCharsRead <= SizeOfVector128InChars, "We should've made forward progress of at least one char.");
+ Debug.Assert((nuint)numCharsRead <= bufferLength, "We shouldn't have read past the end of the input buffer.");
+#endif
+
+ // Adjust remaining buffer length.
+
+ bufferLength += (nuint)pOriginalBuffer;
+ bufferLength -= (nuint)pBuffer;
+
+ // The buffer is now properly aligned.
+ // Read 2 vectors at a time if possible.
+
+ if (bufferLength >= 2 * SizeOfVector128InBytes)
+ {
+ char* pFinalVectorReadPos = (char*)((nuint)pBuffer + bufferLength - 2 * SizeOfVector128InBytes);
+
+ // After this point, we no longer need to update the bufferLength value.
+
+ do
+ {
+ firstVector = Sse2.LoadAlignedVector128((short*)pBuffer);
+ secondVector = Sse2.LoadAlignedVector128((short*)pBuffer + SizeOfVector128InChars);
+ Vector128<short> combinedVector = Sse2.Or(firstVector, secondVector);
+
+ if (Sse41.IsSupported)
+ {
+ // If a non-ASCII bit is set in any WORD of the combined vector, we have seen non-ASCII data.
+ // Jump to the non-ASCII handler to figure out which particular vector contained non-ASCII data.
+ if (!Sse41.TestZ(combinedVector, asciiMaskForPTEST))
+ {
+ goto FoundNonAsciiDataInFirstOrSecondVector;
+ }
+ }
+ else
+ {
+ // See comment earlier in the method for an explanation of how the below logic works.
+ if (Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(combinedVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte()) != 0)
+ {
+ goto FoundNonAsciiDataInFirstOrSecondVector;
+ }
+ }
+
+ pBuffer += 2 * SizeOfVector128InChars;
+ } while (pBuffer <= pFinalVectorReadPos);
+ }
+
+ // We have somewhere between 0 and (2 * vector length) - 1 bytes remaining to read from.
+ // Since the above loop doesn't update bufferLength, we can't rely on its absolute value.
+ // But we _can_ rely on it to tell us how much remaining data must be drained by looking
+ // at what bits of it are set. This works because had we updated it within the loop above,
+ // we would've been adding 2 * SizeOfVector128 on each iteration, but we only care about
+ // bits which are less significant than those that the addition would've acted on.
+
+ // If there is fewer than one vector length remaining, skip the next aligned read.
+ // Remember, at this point bufferLength is measured in bytes, not chars.
+
+ if ((bufferLength & SizeOfVector128InBytes) == 0)
+ {
+ goto DoFinalUnalignedVectorRead;
+ }
+
+ // At least one full vector's worth of data remains, so we can safely read it.
+ // Remember, at this point pBuffer is still aligned.
+
+ firstVector = Sse2.LoadAlignedVector128((short*)pBuffer);
+
+ if (Sse41.IsSupported)
+ {
+ // If a non-ASCII bit is set in any WORD of the combined vector, we have seen non-ASCII data.
+ // Jump to the non-ASCII handler to figure out which particular vector contained non-ASCII data.
+ if (!Sse41.TestZ(firstVector, asciiMaskForPTEST))
+ {
+ goto FoundNonAsciiDataInFirstVector;
+ }
+ }
+ else
+ {
+ // See comment earlier in the method for an explanation of how the below logic works.
+ currentMask = (uint)Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(firstVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte());
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+ }
+
+ IncrementCurrentOffsetBeforeFinalUnalignedVectorRead:
+
+ pBuffer += SizeOfVector128InChars;
+
+ DoFinalUnalignedVectorRead:
+
+ if (((byte)bufferLength & (SizeOfVector128InBytes - 1)) != 0)
+ {
+ // Perform an unaligned read of the last vector.
+ // We need to adjust the pointer because we're re-reading data.
+
+ pBuffer = (char*)((byte*)pBuffer + (bufferLength & (SizeOfVector128InBytes - 1)) - SizeOfVector128InBytes);
+ firstVector = Sse2.LoadVector128((short*)pBuffer); // unaligned load
+
+ if (Sse41.IsSupported)
+ {
+ // If a non-ASCII bit is set in any WORD of the combined vector, we have seen non-ASCII data.
+ // Jump to the non-ASCII handler to figure out which particular vector contained non-ASCII data.
+ if (!Sse41.TestZ(firstVector, asciiMaskForPTEST))
+ {
+ goto FoundNonAsciiDataInFirstVector;
+ }
+ }
+ else
+ {
+ // See comment earlier in the method for an explanation of how the below logic works.
+ currentMask = (uint)Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(firstVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte());
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+ }
+
+ pBuffer += SizeOfVector128InChars;
+ }
+
+ Finish:
+
+ Debug.Assert(((nuint)pBuffer - (nuint)pOriginalBuffer) % 2 == 0, "Shouldn't have incremented any pointer by an odd byte count.");
+ return ((nuint)pBuffer - (nuint)pOriginalBuffer) / sizeof(char); // and we're done! (remember to adjust for char count)
+
+ FoundNonAsciiDataInFirstOrSecondVector:
+
+ // We don't know if the first or the second vector contains non-ASCII data. Check the first
+ // vector, and if that's all-ASCII then the second vector must be the culprit. Either way
+ // we'll make sure the first vector local is the one that contains the non-ASCII data.
+
+ // See comment earlier in the method for an explanation of how the below logic works.
+ if (Sse41.IsSupported)
+ {
+ if (!Sse41.TestZ(firstVector, asciiMaskForPTEST))
+ {
+ goto FoundNonAsciiDataInFirstVector;
+ }
+ }
+ else
+ {
+ currentMask = (uint)Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(firstVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte());
+ if (currentMask != 0)
+ {
+ goto FoundNonAsciiDataInCurrentMask;
+ }
+ }
+
+ // Wasn't the first vector; must be the second.
+
+ pBuffer += SizeOfVector128InChars;
+ firstVector = secondVector;
+
+ FoundNonAsciiDataInFirstVector:
+
+ // See comment earlier in the method for an explanation of how the below logic works.
+ if (Sse41.IsSupported)
+ {
+ currentMask = (uint)Sse2.MoveMask(Sse41.Min(firstVector.AsUInt16(), asciiMaskForPMINUW).AsByte());
+ }
+ else
+ {
+ currentMask = (uint)Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(firstVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte());
+ }
+
+ FoundNonAsciiDataInCurrentMask:
+
+ // The mask contains - from the LSB - a 0 for each ASCII byte we saw, and a 1 for each non-ASCII byte.
+ // Tzcnt is the correct operation to count the number of zero bits quickly. If this instruction isn't
+ // available, we'll fall back to a normal loop. (Even though the original vector used WORD elements,
+ // masks work on BYTE elements, and we account for this in the final fixup.)
+
+ Debug.Assert(currentMask != 0, "Shouldn't be here unless we see non-ASCII data.");
+ pBuffer = (char*)((byte*)pBuffer + (uint)BitOperations.TrailingZeroCount(currentMask));
+
+ goto Finish;
+
+ FoundNonAsciiDataInCurrentDWord:
+
+ uint currentDWord;
+ Debug.Assert(!AllCharsInUInt32AreAscii(currentDWord), "Shouldn't be here unless we see non-ASCII data.");
+
+ if (FirstCharInUInt32IsAscii(currentDWord))
+ {
+ pBuffer++; // skip past the ASCII char
+ }
+
+ goto Finish;
+
+ InputBufferLessThanOneVectorInLength:
+
+ // These code paths get hit if the original input length was less than one vector in size.
+ // We can't perform vectorized reads at this point, so we'll fall back to reading primitives
+ // directly. Note that all of these reads are unaligned.
+
+ // Reminder: If this code path is hit, bufferLength is still a char count, not a byte count.
+ // We skipped the code path that multiplied the count by sizeof(char).
+
+ Debug.Assert(bufferLength < SizeOfVector128InChars);
+
+ // QWORD drain
+
+ if ((bufferLength & 4) != 0)
+ {
+ if (Bmi1.X64.IsSupported)
+ {
+ // If we can use 64-bit tzcnt to count the number of leading ASCII chars, prefer it.
+
+ ulong candidateUInt64 = Unsafe.ReadUnaligned<ulong>(pBuffer);
+ if (!AllCharsInUInt64AreAscii(candidateUInt64))
+ {
+ // Clear the low 7 bits (the ASCII bits) of each char, then tzcnt.
+ // Remember the / 8 at the end to convert bit count to byte count,
+ // then the & ~1 at the end to treat a match in the high byte of
+ // any char the same as a match in the low byte of that same char.
+
+ candidateUInt64 &= 0xFF80FF80_FF80FF80ul;
+ pBuffer = (char*)((byte*)pBuffer + ((nuint)(Bmi1.X64.TrailingZeroCount(candidateUInt64) / 8) & ~(nuint)1));
+ goto Finish;
+ }
+ }
+ else
+ {
+ // If we can't use 64-bit tzcnt, no worries. We'll just do 2x 32-bit reads instead.
+
+ currentDWord = Unsafe.ReadUnaligned<uint>(pBuffer);
+ uint nextDWord = Unsafe.ReadUnaligned<uint>(pBuffer + 4 / sizeof(char));
+
+ if (!AllCharsInUInt32AreAscii(currentDWord | nextDWord))
+ {
+ // At least one of the values wasn't all-ASCII.
+ // We need to figure out which one it was and stick it in the currentMask local.
+
+ if (AllCharsInUInt32AreAscii(currentDWord))
+ {
+ currentDWord = nextDWord; // this one is the culprit
+ pBuffer += 4 / sizeof(char);
+ }
+
+ goto FoundNonAsciiDataInCurrentDWord;
+ }
+ }
+
+ pBuffer += 4; // successfully consumed 4 ASCII chars
+ }
+
+ // DWORD drain
+
+ if ((bufferLength & 2) != 0)
+ {
+ currentDWord = Unsafe.ReadUnaligned<uint>(pBuffer);
+
+ if (!AllCharsInUInt32AreAscii(currentDWord))
+ {
+ goto FoundNonAsciiDataInCurrentDWord;
+ }
+
+ pBuffer += 2; // successfully consumed 2 ASCII chars
+ }
+
+ // WORD drain
+ // This is the final drain; there's no need for a BYTE drain since our elemental type is 16-bit char.
+
+ if ((bufferLength & 1) != 0)
+ {
+ if (*pBuffer <= 0x007F)
+ {
+ pBuffer++; // successfully consumed a single char
+ }
+ }
+
+ goto Finish;
+ }
+
+ /// <summary>
+ /// Given a QWORD which represents a buffer of 4 ASCII chars in machine-endian order,
+ /// narrows each WORD to a BYTE, then writes the 4-byte result to the output buffer
+ /// also in machine-endian order.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+ private static void NarrowFourUtf16CharsToAsciiAndWriteToBuffer(ref byte outputBuffer, ulong value)
+ {
+ Debug.Assert(AllCharsInUInt64AreAscii(value));
+
+ if (Bmi2.X64.IsSupported)
+ {
+ // BMI2 will work regardless of the processor's endianness.
+ Unsafe.WriteUnaligned(ref outputBuffer, (uint)Bmi2.X64.ParallelBitExtract(value, 0x00FF00FF_00FF00FFul));
+ }
+ else
+ {
+ if (BitConverter.IsLittleEndian)
+ {
+ outputBuffer = (byte)value;
+ value >>= 16;
+ Unsafe.Add(ref outputBuffer, 1) = (byte)value;
+ value >>= 16;
+ Unsafe.Add(ref outputBuffer, 2) = (byte)value;
+ value >>= 16;
+ Unsafe.Add(ref outputBuffer, 3) = (byte)value;
+ }
+ else
+ {
+ Unsafe.Add(ref outputBuffer, 3) = (byte)value;
+ value >>= 16;
+ Unsafe.Add(ref outputBuffer, 2) = (byte)value;
+ value >>= 16;
+ Unsafe.Add(ref outputBuffer, 1) = (byte)value;
+ value >>= 16;
+ outputBuffer = (byte)value;
+ }
+ }
+ }
+
+ /// <summary>
+ /// Given a DWORD which represents a buffer of 2 ASCII chars in machine-endian order,
+ /// narrows each WORD to a BYTE, then writes the 2-byte result to the output buffer also in
+ /// machine-endian order.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+ private static void NarrowTwoUtf16CharsToAsciiAndWriteToBuffer(ref byte outputBuffer, uint value)
+ {
+ Debug.Assert(AllCharsInUInt32AreAscii(value));
+
+ if (BitConverter.IsLittleEndian)
+ {
+ outputBuffer = (byte)value;
+ Unsafe.Add(ref outputBuffer, 1) = (byte)(value >> 16);
+ }
+ else
+ {
+ Unsafe.Add(ref outputBuffer, 1) = (byte)value;
+ outputBuffer = (byte)(value >> 16);
+ }
+ }
+
+ /// <summary>
+ /// Copies as many ASCII characters (U+0000..U+007F) as possible from <paramref name="pUtf16Buffer"/>
+ /// to <paramref name="pAsciiBuffer"/>, stopping when the first non-ASCII character is encountered
+ /// or once <paramref name="elementCount"/> elements have been converted. Returns the total number
+ /// of elements that were able to be converted.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveOptimization)]
+ public static unsafe nuint NarrowUtf16ToAscii(char* pUtf16Buffer, byte* pAsciiBuffer, nuint elementCount)
+ {
+ nuint currentOffset = 0;
+
+ uint utf16Data32BitsHigh = 0, utf16Data32BitsLow = 0;
+ ulong utf16Data64Bits = 0;
+
+ // If SSE2 is supported, use those specific intrinsics instead of the generic vectorized
+ // code below. This has two benefits: (a) we can take advantage of specific instructions like
+ // pmovmskb, ptest, vpminuw which we know are optimized, and (b) we can avoid downclocking the
+ // processor while this method is running.
+
+ if (Sse2.IsSupported)
+ {
+ Debug.Assert(BitConverter.IsLittleEndian, "Assume little endian if SSE2 is supported.");
+
+ if (elementCount >= 2 * (uint)Unsafe.SizeOf<Vector128<byte>>())
+ {
+ // Since there's overhead to setting up the vectorized code path, we only want to
+ // call into it after a quick probe to ensure the next immediate characters really are ASCII.
+ // If we see non-ASCII data, we'll jump immediately to the draining logic at the end of the method.
+
+ if (IntPtr.Size >= 8)
+ {
+ utf16Data64Bits = Unsafe.ReadUnaligned<ulong>(pUtf16Buffer);
+ if (!AllCharsInUInt64AreAscii(utf16Data64Bits))
+ {
+ goto FoundNonAsciiDataIn64BitRead;
+ }
+ }
+ else
+ {
+ utf16Data32BitsHigh = Unsafe.ReadUnaligned<uint>(pUtf16Buffer);
+ utf16Data32BitsLow = Unsafe.ReadUnaligned<uint>(pUtf16Buffer + 4 / sizeof(char));
+ if (!AllCharsInUInt32AreAscii(utf16Data32BitsHigh | utf16Data32BitsLow))
+ {
+ goto FoundNonAsciiDataIn64BitRead;
+ }
+ }
+
+ currentOffset = NarrowUtf16ToAscii_Sse2(pUtf16Buffer, pAsciiBuffer, elementCount);
+ }
+ }
+ else if (Vector.IsHardwareAccelerated)
+ {
+ uint SizeOfVector = (uint)Unsafe.SizeOf<Vector<byte>>(); // JIT will make this a const
+
+ // Only bother vectorizing if we have enough data to do so.
+ if (elementCount >= 2 * SizeOfVector)
+ {
+ // Since there's overhead to setting up the vectorized code path, we only want to
+ // call into it after a quick probe to ensure the next immediate characters really are ASCII.
+ // If we see non-ASCII data, we'll jump immediately to the draining logic at the end of the method.
+
+ if (IntPtr.Size >= 8)
+ {
+ utf16Data64Bits = Unsafe.ReadUnaligned<ulong>(pUtf16Buffer);
+ if (!AllCharsInUInt64AreAscii(utf16Data64Bits))
+ {
+ goto FoundNonAsciiDataIn64BitRead;
+ }
+ }
+ else
+ {
+ utf16Data32BitsHigh = Unsafe.ReadUnaligned<uint>(pUtf16Buffer);
+ utf16Data32BitsLow = Unsafe.ReadUnaligned<uint>(pUtf16Buffer + 4 / sizeof(char));
+ if (!AllCharsInUInt32AreAscii(utf16Data32BitsHigh | utf16Data32BitsLow))
+ {
+ goto FoundNonAsciiDataIn64BitRead;
+ }
+ }
+
+ Vector<ushort> maxAscii = new Vector<ushort>(0x007F);
+
+ nuint finalOffsetWhereCanLoop = elementCount - 2 * SizeOfVector;
+ do
+ {
+ Vector<ushort> utf16VectorHigh = Unsafe.ReadUnaligned<Vector<ushort>>(pUtf16Buffer + currentOffset);
+ Vector<ushort> utf16VectorLow = Unsafe.ReadUnaligned<Vector<ushort>>(pUtf16Buffer + currentOffset + Vector<ushort>.Count);
+
+ if (Vector.GreaterThanAny(Vector.BitwiseOr(utf16VectorHigh, utf16VectorLow), maxAscii))
+ {
+ break; // found non-ASCII data
+ }
+
+ // TODO: Is the below logic also valid for big-endian platforms?
+ Vector<byte> asciiVector = Vector.Narrow(utf16VectorHigh, utf16VectorLow);
+ Unsafe.WriteUnaligned<Vector<byte>>(pAsciiBuffer + currentOffset, asciiVector);
+
+ currentOffset += SizeOfVector;
+ } while (currentOffset <= finalOffsetWhereCanLoop);
+ }
+ }
+
+ Debug.Assert(currentOffset <= elementCount);
+ nuint remainingElementCount = elementCount - currentOffset;
+
+ // Try to narrow 64 bits -> 32 bits at a time.
+ // We needn't update remainingElementCount after this point.
+
+ if (remainingElementCount >= 4)
+ {
+ nuint finalOffsetWhereCanLoop = currentOffset + remainingElementCount - 4;
+ do
+ {
+ if (IntPtr.Size >= 8)
+ {
+ // Only perform QWORD reads on a 64-bit platform.
+ utf16Data64Bits = Unsafe.ReadUnaligned<ulong>(pUtf16Buffer + currentOffset);
+ if (!AllCharsInUInt64AreAscii(utf16Data64Bits))
+ {
+ goto FoundNonAsciiDataIn64BitRead;
+ }
+
+ NarrowFourUtf16CharsToAsciiAndWriteToBuffer(ref pAsciiBuffer[currentOffset], utf16Data64Bits);
+ }
+ else
+ {
+ utf16Data32BitsHigh = Unsafe.ReadUnaligned<uint>(pUtf16Buffer + currentOffset);
+ utf16Data32BitsLow = Unsafe.ReadUnaligned<uint>(pUtf16Buffer + currentOffset + 4 / sizeof(char));
+ if (!AllCharsInUInt32AreAscii(utf16Data32BitsHigh | utf16Data32BitsLow))
+ {
+ goto FoundNonAsciiDataIn64BitRead;
+ }
+
+ NarrowTwoUtf16CharsToAsciiAndWriteToBuffer(ref pAsciiBuffer[currentOffset], utf16Data32BitsHigh);
+ NarrowTwoUtf16CharsToAsciiAndWriteToBuffer(ref pAsciiBuffer[currentOffset + 2], utf16Data32BitsLow);
+ }
+
+ currentOffset += 4;
+ } while (currentOffset <= finalOffsetWhereCanLoop);
+ }
+
+ // Try to narrow 32 bits -> 16 bits.
+
+ if (((uint)remainingElementCount & 2) != 0)
+ {
+ utf16Data32BitsHigh = Unsafe.ReadUnaligned<uint>(pUtf16Buffer + currentOffset);
+ if (!AllCharsInUInt32AreAscii(utf16Data32BitsHigh))
+ {
+ goto FoundNonAsciiDataInHigh32Bits;
+ }
+
+ NarrowTwoUtf16CharsToAsciiAndWriteToBuffer(ref pAsciiBuffer[currentOffset], utf16Data32BitsHigh);
+ currentOffset += 2;
+ }
+
+ // Try to narrow 16 bits -> 8 bits.
+
+ if (((uint)remainingElementCount & 1) != 0)
+ {
+ utf16Data32BitsHigh = pUtf16Buffer[currentOffset];
+ if (utf16Data32BitsHigh <= 0x007Fu)
+ {
+ pAsciiBuffer[currentOffset] = (byte)utf16Data32BitsHigh;
+ currentOffset++;
+ }
+ }
+
+ Finish:
+
+ return currentOffset;
+
+ FoundNonAsciiDataIn64BitRead:
+
+ if (IntPtr.Size >= 8)
+ {
+ // Try checking the first 32 bits of the buffer for non-ASCII data.
+ // Regardless, we'll move the non-ASCII data into the utf16Data32BitsHigh local.
+
+ if (BitConverter.IsLittleEndian)
+ {
+ utf16Data32BitsHigh = (uint)utf16Data64Bits;
+ }
+ else
+ {
+ utf16Data32BitsHigh = (uint)(utf16Data64Bits >> 32);
+ }
+
+ if (AllCharsInUInt32AreAscii(utf16Data32BitsHigh))
+ {
+ NarrowTwoUtf16CharsToAsciiAndWriteToBuffer(ref pAsciiBuffer[currentOffset], utf16Data32BitsHigh);
+
+ if (BitConverter.IsLittleEndian)
+ {
+ utf16Data32BitsHigh = (uint)(utf16Data64Bits >> 32);
+ }
+ else
+ {
+ utf16Data32BitsHigh = (uint)utf16Data64Bits;
+ }
+
+ currentOffset += 2;
+ }
+ }
+ else
+ {
+ // Need to determine if the high or the low 32-bit value contained non-ASCII data.
+ // Regardless, we'll move the non-ASCII data into the utf16Data32BitsHigh local.
+
+ if (AllCharsInUInt32AreAscii(utf16Data32BitsHigh))
+ {
+ NarrowTwoUtf16CharsToAsciiAndWriteToBuffer(ref pAsciiBuffer[currentOffset], utf16Data32BitsHigh);
+ utf16Data32BitsHigh = utf16Data32BitsLow;
+ currentOffset += 2;
+ }
+ }
+
+ FoundNonAsciiDataInHigh32Bits:
+
+ Debug.Assert(!AllCharsInUInt32AreAscii(utf16Data32BitsHigh), "Shouldn't have reached this point if we have an all-ASCII input.");
+
+ // There's at most one char that needs to be drained.
+
+ if (FirstCharInUInt32IsAscii(utf16Data32BitsHigh))
+ {
+ if (!BitConverter.IsLittleEndian)
+ {
+ utf16Data32BitsHigh >>= 16; // move high char down to low char
+ }
+
+ pAsciiBuffer[currentOffset] = (byte)utf16Data32BitsHigh;
+ currentOffset++;
+ }
+
+ goto Finish;
+ }
+
+ [MethodImpl(MethodImplOptions.AggressiveOptimization)]
+ private static unsafe nuint NarrowUtf16ToAscii_Sse2(char* pUtf16Buffer, byte* pAsciiBuffer, nuint elementCount)
+ {
+ // This method contains logic optimized for both SSE2 and SSE41. Much of the logic in this method
+ // will be elided by JIT once we determine which specific ISAs we support.
+
+ // JIT turns the below into constants
+
+ uint SizeOfVector128 = (uint)Unsafe.SizeOf<Vector128<byte>>();
+ nuint MaskOfAllBitsInVector128 = (nuint)(SizeOfVector128 - 1);
+
+ // This method is written such that control generally flows top-to-bottom, avoiding
+ // jumps as much as possible in the optimistic case of "all ASCII". If we see non-ASCII
+ // data, we jump out of the hot paths to targets at the end of the method.
+
+ Debug.Assert(Sse2.IsSupported);
+ Debug.Assert(BitConverter.IsLittleEndian);
+ Debug.Assert(elementCount >= 2 * SizeOfVector128);
+
+ Vector128<short> asciiMaskForPTEST = Vector128.Create(unchecked((short)0xFF80)); // used for PTEST on supported hardware
+ Vector128<short> asciiMaskForPXOR = Vector128.Create(unchecked((short)0x8000)); // used for PXOR
+ Vector128<short> asciiMaskForPCMPGTW = Vector128.Create(unchecked((short)0x807F)); // used for PCMPGTW
+
+ // First, perform an unaligned read of the first part of the input buffer.
+
+ Vector128<short> utf16VectorFirst = Sse2.LoadVector128((short*)pUtf16Buffer); // unaligned load
+
+ // If there's non-ASCII data in the first 8 elements of the vector, there's nothing we can do.
+ // See comments in GetIndexOfFirstNonAsciiChar_Sse2 for information about how this works.
+
+ if (Sse41.IsSupported)
+ {
+ if (!Sse41.TestZ(utf16VectorFirst, asciiMaskForPTEST))
+ {
+ return 0;
+ }
+ }
+ else
+ {
+ if (Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(utf16VectorFirst, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte()) != 0)
+ {
+ return 0;
+ }
+ }
+
+ // Turn the 8 ASCII chars we just read into 8 ASCII bytes, then copy it to the destination.
+
+ Vector128<byte> asciiVector = Sse2.PackUnsignedSaturate(utf16VectorFirst, utf16VectorFirst);
+
+ if (Sse41.X64.IsSupported)
+ {
+ // Use PEXTRQ instruction if available, since it can extract from the vector directly to the destination address.
+ Unsafe.WriteUnaligned<ulong>(pAsciiBuffer, Sse41.X64.Extract(asciiVector.AsUInt64(), 0));
+ }
+ else
+ {
+ // Bounce this through a temporary register (with potential stack spillage) before writing to memory.
+ Unsafe.WriteUnaligned<ulong>(pAsciiBuffer, asciiVector.AsUInt64().GetElement(0));
+ }
+
+ nuint currentOffsetInElements = SizeOfVector128 / 2; // we processed 8 elements so far
+
+ // We're going to get the best performance when we have aligned writes, so we'll take the
+ // hit of potentially unaligned reads in order to hit this sweet spot.
+
+ // pAsciiBuffer points to the start of the destination buffer, immediately before where we wrote
+ // the 8 bytes previously. If the 0x08 bit is set at the pinned address, then the 8 bytes we wrote
+ // previously mean that the 0x08 bit is *not* set at address &pAsciiBuffer[SizeOfVector128 / 2]. In
+ // that case we can immediately back up to the previous aligned boundary and start the main loop.
+ // If the 0x08 bit is *not* set at the pinned address, then it means the 0x08 bit *is* set at
+ // address &pAsciiBuffer[SizeOfVector128 / 2], and we should perform one more 8-byte write to bump
+ // just past the next aligned boundary address.
+
+ if (((uint)pAsciiBuffer & (SizeOfVector128 / 2)) == 0)
+ {
+ // We need to perform one more partial vector write before we can get the alignment we want.
+
+ utf16VectorFirst = Sse2.LoadVector128((short*)pUtf16Buffer + currentOffsetInElements); // unaligned load
+
+ // See comments earlier in this method for information about how this works.
+ if (Sse41.IsSupported)
+ {
+ if (!Sse41.TestZ(utf16VectorFirst, asciiMaskForPTEST))
+ {
+ goto Finish;
+ }
+ }
+ else
+ {
+ if (Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(utf16VectorFirst, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte()) != 0)
+ {
+ goto Finish;
+ }
+ }
+
+ // Turn the 8 ASCII chars we just read into 8 ASCII bytes, then copy it to the destination.
+ asciiVector = Sse2.PackUnsignedSaturate(utf16VectorFirst, utf16VectorFirst);
+
+ // See comments earlier in this method for information about how this works.
+ if (Sse41.X64.IsSupported)
+ {
+ Unsafe.WriteUnaligned<ulong>(pAsciiBuffer + currentOffsetInElements, Sse41.X64.Extract(asciiVector.AsUInt64(), 0));
+ }
+ else
+ {
+ Unsafe.WriteUnaligned<ulong>(pAsciiBuffer + currentOffsetInElements, asciiVector.AsUInt64().GetElement(0));
+ }
+ }
+
+ // Calculate how many elements we wrote in order to get pAsciiBuffer to its next alignment
+ // point, then use that as the base offset going forward.
+
+ currentOffsetInElements = SizeOfVector128 - ((nuint)pAsciiBuffer & MaskOfAllBitsInVector128);
+ Debug.Assert(0 < currentOffsetInElements && currentOffsetInElements <= SizeOfVector128, "We wrote at least 1 byte but no more than a whole vector.");
+
+ Debug.Assert(currentOffsetInElements <= elementCount, "Shouldn't have overrun the destination buffer.");
+ Debug.Assert(elementCount - currentOffsetInElements >= SizeOfVector128, "We should be able to run at least one whole vector.");
+
+ nuint finalOffsetWhereCanRunLoop = elementCount - SizeOfVector128;
+ do
+ {
+ // In a loop, perform two unaligned reads, narrow to a single vector, then aligned write one vector.
+
+ utf16VectorFirst = Sse2.LoadVector128((short*)pUtf16Buffer + currentOffsetInElements); // unaligned load
+ Vector128<short> utf16VectorSecond = Sse2.LoadVector128((short*)pUtf16Buffer + currentOffsetInElements + SizeOfVector128 / sizeof(short)); // unaligned load
+ Vector128<short> combinedVector = Sse2.Or(utf16VectorFirst, utf16VectorSecond);
+
+ // See comments in GetIndexOfFirstNonAsciiChar_Sse2 for information about how this works.
+ if (Sse41.IsSupported)
+ {
+ if (!Sse41.TestZ(combinedVector, asciiMaskForPTEST))
+ {
+ goto FoundNonAsciiDataInLoop;
+ }
+ }
+ else
+ {
+ if (Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(combinedVector, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte()) != 0)
+ {
+ goto FoundNonAsciiDataInLoop;
+ }
+ }
+
+ // Build up the UTF-8 vector and perform the store.
+
+ asciiVector = Sse2.PackUnsignedSaturate(utf16VectorFirst, utf16VectorSecond);
+
+ Debug.Assert(((nuint)pAsciiBuffer + currentOffsetInElements) % SizeOfVector128 == 0, "Write should be aligned.");
+ Sse2.StoreAligned(pAsciiBuffer + currentOffsetInElements, asciiVector); // aligned
+
+ currentOffsetInElements += SizeOfVector128;
+ } while (currentOffsetInElements <= finalOffsetWhereCanRunLoop);
+
+ Finish:
+
+ // There might be some ASCII data left over. That's fine - we'll let our caller handle the final drain.
+ return currentOffsetInElements;
+
+ FoundNonAsciiDataInLoop:
+
+ // Can we at least narrow the high vector?
+ // See comments in GetIndexOfFirstNonAsciiChar_Sse2 for information about how this works.
+ if (Sse41.IsSupported)
+ {
+ if (!Sse41.TestZ(utf16VectorFirst, asciiMaskForPTEST))
+ {
+ goto Finish; // found non-ASCII data
+ }
+ }
+ else
+ {
+ if (Sse2.MoveMask(Sse2.CompareGreaterThan(Sse2.Xor(utf16VectorFirst, asciiMaskForPXOR), asciiMaskForPCMPGTW).AsByte()) != 0)
+ {
+ goto Finish; // found non-ASCII data
+ }
+ }
+
+ // First part was all ASCII, narrow and aligned write. Note we're only filling in the low half of the vector.
+ asciiVector = Sse2.PackUnsignedSaturate(utf16VectorFirst, utf16VectorFirst);
+
+ Debug.Assert(((nuint)pAsciiBuffer + currentOffsetInElements) % sizeof(ulong) == 0, "Destination should be ulong-aligned.");
+
+ // See comments earlier in this method for information about how this works.
+ if (Sse41.X64.IsSupported)
+ {
+ *(ulong*)(pAsciiBuffer + currentOffsetInElements) = Sse41.X64.Extract(asciiVector.AsUInt64(), 0);
+ }
+ else
+ {
+ *(ulong*)(pAsciiBuffer + currentOffsetInElements) = asciiVector.AsUInt64().GetElement(0);
+ }
+ currentOffsetInElements += SizeOfVector128 / 2;
+
+ goto Finish;
+ }
+
+ /// <summary>
+ /// Rotates a <see cref="uint"/> left. The JIT is smart enough to turn this into a ROL / ROR instruction.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ private static uint ROL32(uint value, int shift) => (value << shift) | (value >> (32 - shift));
+
+ /// <summary>
+ /// Copies as many ASCII bytes (00..7F) as possible from <paramref name="pAsciiBuffer"/>
+ /// to <paramref name="pUtf16Buffer"/>, stopping when the first non-ASCII byte is encountered
+ /// or once <paramref name="elementCount"/> elements have been converted. Returns the total number
+ /// of elements that were able to be converted.
+ /// </summary>
+ public static unsafe nuint WidenAsciiToUtf16(byte* pAsciiBuffer, char* pUtf16Buffer, nuint elementCount)
+ {
+ nuint currentOffset = 0;
+
+ // If SSE2 is supported, use those specific intrinsics instead of the generic vectorized
+ // code below. This has two benefits: (a) we can take advantage of specific instructions like
+ // pmovmskb which we know are optimized, and (b) we can avoid downclocking the processor while
+ // this method is running.
+
+ if (Sse2.IsSupported)
+ {
+ if (elementCount >= 2 * (uint)Unsafe.SizeOf<Vector128<byte>>())
+ {
+ currentOffset = WidenAsciiToUtf16_Sse2(pAsciiBuffer, pUtf16Buffer, elementCount);
+ }
+ }
+ else if (Vector.IsHardwareAccelerated)
+ {
+ uint SizeOfVector = (uint)Unsafe.SizeOf<Vector<byte>>(); // JIT will make this a const
+
+ // Only bother vectorizing if we have enough data to do so.
+ if (elementCount >= SizeOfVector)
+ {
+ // Note use of SBYTE instead of BYTE below; we're using the two's-complement
+ // representation of negative integers to act as a surrogate for "is ASCII?".
+
+ nuint finalOffsetWhereCanLoop = elementCount - SizeOfVector;
+ do
+ {
+ Vector<sbyte> asciiVector = Unsafe.ReadUnaligned<Vector<sbyte>>(pAsciiBuffer + currentOffset);
+ if (Vector.LessThanAny(asciiVector, Vector<sbyte>.Zero))
+ {
+ break; // found non-ASCII data
+ }
+
+ Vector.Widen(Vector.AsVectorByte(asciiVector), out Vector<ushort> utf16LowVector, out Vector<ushort> utf16HighVector);
+
+ // TODO: Is the below logic also valid for big-endian platforms?
+ Unsafe.WriteUnaligned<Vector<ushort>>(pUtf16Buffer + currentOffset, utf16LowVector);
+ Unsafe.WriteUnaligned<Vector<ushort>>(pUtf16Buffer + currentOffset + Vector<ushort>.Count, utf16HighVector);
+
+ currentOffset += SizeOfVector;
+ } while (currentOffset <= finalOffsetWhereCanLoop);
+ }
+ }
+
+ Debug.Assert(currentOffset <= elementCount);
+ nuint remainingElementCount = elementCount - currentOffset;
+
+ // Try to widen 32 bits -> 64 bits at a time.
+ // We needn't update remainingElementCount after this point.
+
+ uint asciiData;
+
+ if (remainingElementCount >= 4)
+ {
+ nuint finalOffsetWhereCanLoop = currentOffset + remainingElementCount - 4;
+ do
+ {
+ asciiData = Unsafe.ReadUnaligned<uint>(pAsciiBuffer + currentOffset);
+ if (!AllBytesInUInt32AreAscii(asciiData))
+ {
+ goto FoundNonAsciiData;
+ }
+
+ WidenFourAsciiBytesToUtf16AndWriteToBuffer(ref pUtf16Buffer[currentOffset], asciiData);
+ currentOffset += 4;
+ } while (currentOffset <= finalOffsetWhereCanLoop);
+ }
+
+ // Try to widen 16 bits -> 32 bits.
+
+ if (((uint)remainingElementCount & 2) != 0)
+ {
+ asciiData = Unsafe.ReadUnaligned<ushort>(pAsciiBuffer + currentOffset);
+ if (!AllBytesInUInt32AreAscii(asciiData))
+ {
+ goto FoundNonAsciiData;
+ }
+
+ if (BitConverter.IsLittleEndian)
+ {
+ pUtf16Buffer[currentOffset] = (char)(byte)asciiData;
+ pUtf16Buffer[currentOffset + 1] = (char)(asciiData >> 8);
+ }
+ else
+ {
+ pUtf16Buffer[currentOffset + 1] = (char)(byte)asciiData;
+ pUtf16Buffer[currentOffset] = (char)(asciiData >> 8);
+ }
+
+ currentOffset += 2;
+ }
+
+ // Try to widen 8 bits -> 16 bits.
+
+ if (((uint)remainingElementCount & 1) != 0)
+ {
+ asciiData = pAsciiBuffer[currentOffset];
+ if (((byte)asciiData & 0x80) != 0)
+ {
+ goto Finish;
+ }
+
+ pUtf16Buffer[currentOffset] = (char)asciiData;
+ currentOffset += 1;
+ }
+
+ Finish:
+
+ return currentOffset;
+
+ FoundNonAsciiData:
+
+ Debug.Assert(!AllBytesInUInt32AreAscii(asciiData), "Shouldn't have reached this point if we have an all-ASCII input.");
+
+ // Drain ASCII bytes one at a time.
+
+ while (((byte)asciiData & 0x80) == 0)
+ {
+ pUtf16Buffer[currentOffset] = (char)(byte)asciiData;
+ currentOffset += 1;
+ asciiData >>= 8;
+ }
+
+ goto Finish;
+ }
+
+ [MethodImpl(MethodImplOptions.AggressiveOptimization)]
+ private static unsafe nuint WidenAsciiToUtf16_Sse2(byte* pAsciiBuffer, char* pUtf16Buffer, nuint elementCount)
+ {
+ // JIT turns the below into constants
+
+ uint SizeOfVector128 = (uint)Unsafe.SizeOf<Vector128<byte>>();
+ nuint MaskOfAllBitsInVector128 = (nuint)(SizeOfVector128 - 1);
+
+ // This method is written such that control generally flows top-to-bottom, avoiding
+ // jumps as much as possible in the optimistic case of "all ASCII". If we see non-ASCII
+ // data, we jump out of the hot paths to targets at the end of the method.
+
+ Debug.Assert(Sse2.IsSupported);
+ Debug.Assert(BitConverter.IsLittleEndian);
+ Debug.Assert(elementCount >= 2 * SizeOfVector128);
+
+ // We're going to get the best performance when we have aligned writes, so we'll take the
+ // hit of potentially unaligned reads in order to hit this sweet spot.
+
+ Vector128<byte> asciiVector;
+ Vector128<byte> utf16FirstHalfVector;
+ uint mask;
+
+ // First, perform an unaligned read of the first part of the input buffer.
+
+ asciiVector = Sse2.LoadVector128(pAsciiBuffer); // unaligned load
+ mask = (uint)Sse2.MoveMask(asciiVector);
+
+ // If there's non-ASCII data in the first 8 elements of the vector, there's nothing we can do.
+
+ if ((byte)mask != 0)
+ {
+ return 0;
+ }
+
+ // Then perform an unaligned write of the first part of the input buffer.
+
+ Vector128<byte> zeroVector = Vector128<byte>.Zero;
+
+ utf16FirstHalfVector = Sse2.UnpackLow(asciiVector, zeroVector);
+ Sse2.Store((byte*)pUtf16Buffer, utf16FirstHalfVector); // unaligned
+
+ // Calculate how many elements we wrote in order to get pOutputBuffer to its next alignment
+ // point, then use that as the base offset going forward. Remember the >> 1 to account for
+ // that we wrote chars, not bytes. This means we may re-read data in the next iteration of
+ // the loop, but this is ok.
+
+ nuint currentOffset = (SizeOfVector128 >> 1) - (((nuint)pUtf16Buffer >> 1) & (MaskOfAllBitsInVector128 >> 1));
+ Debug.Assert(0 < currentOffset && currentOffset <= SizeOfVector128 / sizeof(char));
+
+ nuint finalOffsetWhereCanRunLoop = elementCount - SizeOfVector128;
+
+ do
+ {
+ // In a loop, perform an unaligned read, widen to two vectors, then aligned write the two vectors.
+
+ asciiVector = Sse2.LoadVector128(pAsciiBuffer + currentOffset); // unaligned load
+ mask = (uint)Sse2.MoveMask(asciiVector);
+
+ if (mask != 0)
+ {
+ // non-ASCII byte somewhere
+ goto NonAsciiDataSeenInInnerLoop;
+ }
+
+ byte* pStore = (byte*)(pUtf16Buffer + currentOffset);
+ Sse2.StoreAligned(pStore, Sse2.UnpackLow(asciiVector, zeroVector));
+
+ pStore += SizeOfVector128;
+ Sse2.StoreAligned(pStore, Sse2.UnpackHigh(asciiVector, zeroVector));
+
+ currentOffset += SizeOfVector128;
+ } while (currentOffset <= finalOffsetWhereCanRunLoop);
+
+ Finish:
+
+ return currentOffset;
+
+ NonAsciiDataSeenInInnerLoop:
+
+ // Can we at least widen the first part of the vector?
+
+ if ((byte)mask == 0)
+ {
+ // First part was all ASCII, widen
+ utf16FirstHalfVector = Sse2.UnpackLow(asciiVector, zeroVector);
+ Sse2.StoreAligned((byte*)(pUtf16Buffer + currentOffset), utf16FirstHalfVector);
+ currentOffset += SizeOfVector128 / 2;
+ }
+
+ goto Finish;
+ }
+
+ /// <summary>
+ /// Given a DWORD which represents a buffer of 4 bytes, widens the buffer into 4 WORDs and
+ /// writes them to the output buffer with machine endianness.
+ /// </summary>
+ [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+ private static void WidenFourAsciiBytesToUtf16AndWriteToBuffer(ref char outputBuffer, uint value)
+ {
+ Debug.Assert(AllBytesInUInt32AreAscii(value));
+
+ if (Bmi2.X64.IsSupported)
+ {
+ // BMI2 will work regardless of the processor's endianness.
+ Unsafe.WriteUnaligned(ref Unsafe.As<char, byte>(ref outputBuffer), Bmi2.X64.ParallelBitDeposit(value, 0x00FF00FF_00FF00FFul));
+ }
+ else
+ {
+ if (BitConverter.IsLittleEndian)
+ {
+ outputBuffer = (char)(byte)value;
+ value >>= 8;
+ Unsafe.Add(ref outputBuffer, 1) = (char)(byte)value;
+ value >>= 8;
+ Unsafe.Add(ref outputBuffer, 2) = (char)(byte)value;
+ value >>= 8;
+ Unsafe.Add(ref outputBuffer, 3) = (char)value;
+ }
+ else
{
- break;
+ Unsafe.Add(ref outputBuffer, 3) = (char)(byte)value;
+ value >>= 8;
+ Unsafe.Add(ref outputBuffer, 2) = (char)(byte)value;
+ value >>= 8;
+ Unsafe.Add(ref outputBuffer, 1) = (char)(byte)value;
+ value >>= 8;
+ outputBuffer = (char)value;
}
- pChars[idx] = (char)b;
}
- return idx;
}
}
}
projects / platform / upstream / coreclr.git / commitdiff