--- /dev/null
+/* strnlen - calculate the length of a string with limit.
+
+ Copyright (C) 2013 Free Software Foundation, Inc.
+
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library. If not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <sysdep.h>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64
+ */
+
+/* Arguments and results. */
+#define srcin x0
+#define len x0
+#define limit x1
+
+/* Locals and temporaries. */
+#define src x2
+#define data1 x3
+#define data2 x4
+#define data2a x5
+#define has_nul1 x6
+#define has_nul2 x7
+#define tmp1 x8
+#define tmp2 x9
+#define tmp3 x10
+#define tmp4 x11
+#define zeroones x12
+#define pos x13
+#define limit_wd x14
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+#define REP8_80 0x8080808080808080
+
+ENTRY_ALIGN_AND_PAD (__strnlen, 6, 9)
+ cbz limit, L(hit_limit)
+ mov zeroones, #REP8_01
+ bic src, srcin, #15
+ ands tmp1, srcin, #15
+ b.ne L(misaligned)
+ /* Calculate the number of full and partial words -1. */
+ sub limit_wd, limit, #1 /* Limit != 0, so no underflow. */
+ lsr limit_wd, limit_wd, #4 /* Convert to Qwords. */
+
+ /* NUL detection works on the principle that (X - 1) & (~X) & 0x80
+ (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
+ can be done in parallel across the entire word. */
+ /* The inner loop deals with two Dwords at a time. This has a
+ slightly higher start-up cost, but we should win quite quickly,
+ especially on cores with a high number of issue slots per
+ cycle, as we get much better parallelism out of the operations. */
+
+ /* Start of critial section -- keep to one 64Byte cache line. */
+L(loop):
+ ldp data1, data2, [src], #16
+L(realigned):
+ sub tmp1, data1, zeroones
+ orr tmp2, data1, #REP8_7f
+ sub tmp3, data2, zeroones
+ orr tmp4, data2, #REP8_7f
+ bic has_nul1, tmp1, tmp2
+ bic has_nul2, tmp3, tmp4
+ subs limit_wd, limit_wd, #1
+ orr tmp1, has_nul1, has_nul2
+ ccmp tmp1, #0, #0, pl /* NZCV = 0000 */
+ b.eq L(loop)
+ /* End of critical section -- keep to one 64Byte cache line. */
+
+ orr tmp1, has_nul1, has_nul2
+ cbz tmp1, L(hit_limit) /* No null in final Qword. */
+
+ /* We know there's a null in the final Qword. The easiest thing
+ to do now is work out the length of the string and return
+ MIN (len, limit). */
+
+ sub len, src, srcin
+ cbz has_nul1, L(nul_in_data2)
+#ifdef __AARCH64EB__
+ mov data2, data1
+#endif
+ sub len, len, #8
+ mov has_nul2, has_nul1
+L(nul_in_data2):
+#ifdef __AARCH64EB__
+ /* For big-endian, carry propagation (if the final byte in the
+ string is 0x01) means we cannot use has_nul directly. The
+ easiest way to get the correct byte is to byte-swap the data
+ and calculate the syndrome a second time. */
+ rev data2, data2
+ sub tmp1, data2, zeroones
+ orr tmp2, data2, #REP8_7f
+ bic has_nul2, tmp1, tmp2
+#endif
+ sub len, len, #8
+ rev has_nul2, has_nul2
+ clz pos, has_nul2
+ add len, len, pos, lsr #3 /* Bits to bytes. */
+ cmp len, limit
+ csel len, len, limit, ls /* Return the lower value. */
+ RET
+
+L(misaligned):
+ /* Deal with a partial first word.
+ We're doing two things in parallel here;
+ 1) Calculate the number of words (but avoiding overflow if
+ limit is near ULONG_MAX) - to do this we need to work out
+ limit + tmp1 - 1 as a 65-bit value before shifting it;
+ 2) Load and mask the initial data words - we force the bytes
+ before the ones we are interested in to 0xff - this ensures
+ early bytes will not hit any zero detection. */
+ sub limit_wd, limit, #1
+ neg tmp4, tmp1
+ cmp tmp1, #8
+
+ and tmp3, limit_wd, #15
+ lsr limit_wd, limit_wd, #4
+ mov tmp2, #~0
+
+ ldp data1, data2, [src], #16
+ lsl tmp4, tmp4, #3 /* Bytes beyond alignment -> bits. */
+ add tmp3, tmp3, tmp1
+
+#ifdef __AARCH64EB__
+ /* Big-endian. Early bytes are at MSB. */
+ lsl tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */
+#else
+ /* Little-endian. Early bytes are at LSB. */
+ lsr tmp2, tmp2, tmp4 /* Shift (tmp1 & 63). */
+#endif
+ add limit_wd, limit_wd, tmp3, lsr #4
+
+ orr data1, data1, tmp2
+ orr data2a, data2, tmp2
+
+ csinv data1, data1, xzr, le
+ csel data2, data2, data2a, le
+ b L(realigned)
+
+L(hit_limit):
+ mov len, limit
+ RET
+END (__strnlen)
+weak_alias (__strnlen, strnlen)
+libc_hidden_def (strnlen)
projects / external / glibc.git / commitdiff