summaryrefslogtreecommitdiffstats
path: root/arch/arm64/lib/strcmp.S
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /arch/arm64/lib/strcmp.S
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/arm64/lib/strcmp.S')
-rw-r--r--arch/arm64/lib/strcmp.S190
1 files changed, 190 insertions, 0 deletions
diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S
new file mode 100644
index 000000000..9b89b4533
--- /dev/null
+++ b/arch/arm64/lib/strcmp.S
@@ -0,0 +1,190 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2012-2022, Arm Limited.
+ *
+ * Adapted from the original at:
+ * https://github.com/ARM-software/optimized-routines/blob/189dfefe37d54c5b/string/aarch64/strcmp.S
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+/* Assumptions:
+ *
+ * ARMv8-a, AArch64.
+ * MTE compatible.
+ */
+
+#define L(label) .L ## label
+
+#define REP8_01 0x0101010101010101
+#define REP8_7f 0x7f7f7f7f7f7f7f7f
+
+#define src1 x0
+#define src2 x1
+#define result x0
+
+#define data1 x2
+#define data1w w2
+#define data2 x3
+#define data2w w3
+#define has_nul x4
+#define diff x5
+#define off1 x5
+#define syndrome x6
+#define tmp x6
+#define data3 x7
+#define zeroones x8
+#define shift x9
+#define off2 x10
+
+/* On big-endian early bytes are at MSB and on little-endian LSB.
+ LS_FW means shifting towards early bytes. */
+#ifdef __AARCH64EB__
+# define LS_FW lsl
+#else
+# define LS_FW lsr
+#endif
+
+/* 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.
+ Since carry propagation makes 0x1 bytes before a NUL byte appear
+ NUL too in big-endian, byte-reverse the data before the NUL check. */
+
+
+SYM_FUNC_START(__pi_strcmp)
+ sub off2, src2, src1
+ mov zeroones, REP8_01
+ and tmp, src1, 7
+ tst off2, 7
+ b.ne L(misaligned8)
+ cbnz tmp, L(mutual_align)
+
+ .p2align 4
+
+L(loop_aligned):
+ ldr data2, [src1, off2]
+ ldr data1, [src1], 8
+L(start_realigned):
+#ifdef __AARCH64EB__
+ rev tmp, data1
+ sub has_nul, tmp, zeroones
+ orr tmp, tmp, REP8_7f
+#else
+ sub has_nul, data1, zeroones
+ orr tmp, data1, REP8_7f
+#endif
+ bics has_nul, has_nul, tmp /* Non-zero if NUL terminator. */
+ ccmp data1, data2, 0, eq
+ b.eq L(loop_aligned)
+#ifdef __AARCH64EB__
+ rev has_nul, has_nul
+#endif
+ eor diff, data1, data2
+ orr syndrome, diff, has_nul
+L(end):
+#ifndef __AARCH64EB__
+ rev syndrome, syndrome
+ rev data1, data1
+ rev data2, data2
+#endif
+ clz shift, syndrome
+ /* The most-significant-non-zero bit of the syndrome marks either the
+ first bit that is different, or the top bit of the first zero byte.
+ Shifting left now will bring the critical information into the
+ top bits. */
+ lsl data1, data1, shift
+ lsl data2, data2, shift
+ /* But we need to zero-extend (char is unsigned) the value and then
+ perform a signed 32-bit subtraction. */
+ lsr data1, data1, 56
+ sub result, data1, data2, lsr 56
+ ret
+
+ .p2align 4
+
+L(mutual_align):
+ /* Sources are mutually aligned, but are not currently at an
+ alignment boundary. Round down the addresses and then mask off
+ the bytes that precede the start point. */
+ bic src1, src1, 7
+ ldr data2, [src1, off2]
+ ldr data1, [src1], 8
+ neg shift, src2, lsl 3 /* Bits to alignment -64. */
+ mov tmp, -1
+ LS_FW tmp, tmp, shift
+ orr data1, data1, tmp
+ orr data2, data2, tmp
+ b L(start_realigned)
+
+L(misaligned8):
+ /* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always
+ checking to make sure that we don't access beyond the end of SRC2. */
+ cbz tmp, L(src1_aligned)
+L(do_misaligned):
+ ldrb data1w, [src1], 1
+ ldrb data2w, [src2], 1
+ cmp data1w, 0
+ ccmp data1w, data2w, 0, ne /* NZCV = 0b0000. */
+ b.ne L(done)
+ tst src1, 7
+ b.ne L(do_misaligned)
+
+L(src1_aligned):
+ neg shift, src2, lsl 3
+ bic src2, src2, 7
+ ldr data3, [src2], 8
+#ifdef __AARCH64EB__
+ rev data3, data3
+#endif
+ lsr tmp, zeroones, shift
+ orr data3, data3, tmp
+ sub has_nul, data3, zeroones
+ orr tmp, data3, REP8_7f
+ bics has_nul, has_nul, tmp
+ b.ne L(tail)
+
+ sub off1, src2, src1
+
+ .p2align 4
+
+L(loop_unaligned):
+ ldr data3, [src1, off1]
+ ldr data2, [src1, off2]
+#ifdef __AARCH64EB__
+ rev data3, data3
+#endif
+ sub has_nul, data3, zeroones
+ orr tmp, data3, REP8_7f
+ ldr data1, [src1], 8
+ bics has_nul, has_nul, tmp
+ ccmp data1, data2, 0, eq
+ b.eq L(loop_unaligned)
+
+ lsl tmp, has_nul, shift
+#ifdef __AARCH64EB__
+ rev tmp, tmp
+#endif
+ eor diff, data1, data2
+ orr syndrome, diff, tmp
+ cbnz syndrome, L(end)
+L(tail):
+ ldr data1, [src1]
+ neg shift, shift
+ lsr data2, data3, shift
+ lsr has_nul, has_nul, shift
+#ifdef __AARCH64EB__
+ rev data2, data2
+ rev has_nul, has_nul
+#endif
+ eor diff, data1, data2
+ orr syndrome, diff, has_nul
+ b L(end)
+
+L(done):
+ sub result, data1, data2
+ ret
+SYM_FUNC_END(__pi_strcmp)
+SYM_FUNC_ALIAS_WEAK(strcmp, __pi_strcmp)
+EXPORT_SYMBOL_NOKASAN(strcmp)