[ADT/MathExtras] Introduce PowerOf2Ceil.

To be used in lld (and probably somewhere else in llvm).

Differential Revision:  https://reviews.llvm.org/D26538

llvm-svn: 286549

diff --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
index 77b1f74..dd83517 100644 (file)
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -641,6 +641,14 @@ inline uint64_t PowerOf2Floor(uint64_t A) {
   return 1ull << (63 - countLeadingZeros(A, ZB_Undefined));
 }
 
+/// Returns the power of two which is greater than or equal to the given value.
+/// Essentially, it is a ceil operation across the domain of powers of two.
+inline uint64_t PowerOf2Ceil(uint64_t A) {
+  if (!A)
+    return 0;
+  return NextPowerOf2(A - 1);
+}
+
 /// Returns the next integer (mod 2**64) that is greater than or equal to
 /// \p Value and is a multiple of \p Align. \p Align must be non-zero.
 ///

diff --git a/llvm/unittests/Support/MathExtrasTest.cpp b/llvm/unittests/Support/MathExtrasTest.cpp
index d373030..c8c4950 100644 (file)
--- a/llvm/unittests/Support/MathExtrasTest.cpp
+++ b/llvm/unittests/Support/MathExtrasTest.cpp
@@ -165,6 +165,12 @@ TEST(MathExtras, isPowerOf2_64) {
   EXPECT_FALSE(isPowerOf2_64(0xABCDEF0ABCDEF0LL));
 }
 
+TEST(MathExtras, PowerOf2Ceil) {
+  EXPECT_EQ(0, PowerOf2Ceil(0));
+  EXPECT_EQ(8, PowerOf2Ceil(8));
+  EXPECT_EQ(8, PowerOf2Ceil(7));
+}
+
 TEST(MathExtras, ByteSwap_32) {
   EXPECT_EQ(0x44332211u, ByteSwap_32(0x11223344));
   EXPECT_EQ(0xDDCCBBAAu, ByteSwap_32(0xAABBCCDD));