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190 lines
4.2 KiB
190 lines
4.2 KiB
/* SPDX-License-Identifier: GPL-2.0-only */ |
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/* |
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* Copyright (c) 2012-2022, Arm Limited. |
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* |
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* Adapted from the original at: |
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* https://github.com/ARM-software/optimized-routines/blob/189dfefe37d54c5b/string/aarch64/strcmp.S |
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*/ |
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#include <linux/linkage.h> |
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#include <asm/assembler.h> |
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/* Assumptions: |
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* |
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* ARMv8-a, AArch64. |
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* MTE compatible. |
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*/ |
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#define L(label) .L ## label |
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#define REP8_01 0x0101010101010101 |
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#define REP8_7f 0x7f7f7f7f7f7f7f7f |
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#define src1 x0 |
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#define src2 x1 |
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#define result x0 |
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#define data1 x2 |
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#define data1w w2 |
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#define data2 x3 |
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#define data2w w3 |
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#define has_nul x4 |
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#define diff x5 |
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#define off1 x5 |
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#define syndrome x6 |
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#define tmp x6 |
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#define data3 x7 |
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#define zeroones x8 |
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#define shift x9 |
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#define off2 x10 |
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/* On big-endian early bytes are at MSB and on little-endian LSB. |
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LS_FW means shifting towards early bytes. */ |
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#ifdef __AARCH64EB__ |
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# define LS_FW lsl |
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#else |
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# define LS_FW lsr |
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#endif |
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/* NUL detection works on the principle that (X - 1) & (~X) & 0x80 |
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(=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and |
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can be done in parallel across the entire word. |
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Since carry propagation makes 0x1 bytes before a NUL byte appear |
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NUL too in big-endian, byte-reverse the data before the NUL check. */ |
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SYM_FUNC_START(__pi_strcmp) |
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sub off2, src2, src1 |
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mov zeroones, REP8_01 |
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and tmp, src1, 7 |
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tst off2, 7 |
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b.ne L(misaligned8) |
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cbnz tmp, L(mutual_align) |
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.p2align 4 |
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L(loop_aligned): |
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ldr data2, [src1, off2] |
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ldr data1, [src1], 8 |
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L(start_realigned): |
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#ifdef __AARCH64EB__ |
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rev tmp, data1 |
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sub has_nul, tmp, zeroones |
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orr tmp, tmp, REP8_7f |
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#else |
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sub has_nul, data1, zeroones |
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orr tmp, data1, REP8_7f |
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#endif |
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bics has_nul, has_nul, tmp /* Non-zero if NUL terminator. */ |
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ccmp data1, data2, 0, eq |
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b.eq L(loop_aligned) |
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#ifdef __AARCH64EB__ |
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rev has_nul, has_nul |
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#endif |
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eor diff, data1, data2 |
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orr syndrome, diff, has_nul |
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L(end): |
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#ifndef __AARCH64EB__ |
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rev syndrome, syndrome |
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rev data1, data1 |
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rev data2, data2 |
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#endif |
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clz shift, syndrome |
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/* The most-significant-non-zero bit of the syndrome marks either the |
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first bit that is different, or the top bit of the first zero byte. |
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Shifting left now will bring the critical information into the |
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top bits. */ |
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lsl data1, data1, shift |
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lsl data2, data2, shift |
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/* But we need to zero-extend (char is unsigned) the value and then |
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perform a signed 32-bit subtraction. */ |
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lsr data1, data1, 56 |
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sub result, data1, data2, lsr 56 |
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ret |
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.p2align 4 |
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L(mutual_align): |
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/* Sources are mutually aligned, but are not currently at an |
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alignment boundary. Round down the addresses and then mask off |
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the bytes that precede the start point. */ |
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bic src1, src1, 7 |
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ldr data2, [src1, off2] |
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ldr data1, [src1], 8 |
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neg shift, src2, lsl 3 /* Bits to alignment -64. */ |
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mov tmp, -1 |
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LS_FW tmp, tmp, shift |
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orr data1, data1, tmp |
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orr data2, data2, tmp |
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b L(start_realigned) |
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L(misaligned8): |
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/* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always |
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checking to make sure that we don't access beyond the end of SRC2. */ |
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cbz tmp, L(src1_aligned) |
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L(do_misaligned): |
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ldrb data1w, [src1], 1 |
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ldrb data2w, [src2], 1 |
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cmp data1w, 0 |
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ccmp data1w, data2w, 0, ne /* NZCV = 0b0000. */ |
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b.ne L(done) |
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tst src1, 7 |
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b.ne L(do_misaligned) |
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L(src1_aligned): |
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neg shift, src2, lsl 3 |
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bic src2, src2, 7 |
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ldr data3, [src2], 8 |
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#ifdef __AARCH64EB__ |
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rev data3, data3 |
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#endif |
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lsr tmp, zeroones, shift |
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orr data3, data3, tmp |
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sub has_nul, data3, zeroones |
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orr tmp, data3, REP8_7f |
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bics has_nul, has_nul, tmp |
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b.ne L(tail) |
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sub off1, src2, src1 |
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.p2align 4 |
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L(loop_unaligned): |
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ldr data3, [src1, off1] |
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ldr data2, [src1, off2] |
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#ifdef __AARCH64EB__ |
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rev data3, data3 |
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#endif |
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sub has_nul, data3, zeroones |
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orr tmp, data3, REP8_7f |
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ldr data1, [src1], 8 |
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bics has_nul, has_nul, tmp |
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ccmp data1, data2, 0, eq |
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b.eq L(loop_unaligned) |
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lsl tmp, has_nul, shift |
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#ifdef __AARCH64EB__ |
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rev tmp, tmp |
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#endif |
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eor diff, data1, data2 |
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orr syndrome, diff, tmp |
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cbnz syndrome, L(end) |
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L(tail): |
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ldr data1, [src1] |
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neg shift, shift |
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lsr data2, data3, shift |
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lsr has_nul, has_nul, shift |
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#ifdef __AARCH64EB__ |
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rev data2, data2 |
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rev has_nul, has_nul |
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#endif |
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eor diff, data1, data2 |
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orr syndrome, diff, has_nul |
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b L(end) |
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L(done): |
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sub result, data1, data2 |
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ret |
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SYM_FUNC_END(__pi_strcmp) |
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SYM_FUNC_ALIAS_WEAK(strcmp, __pi_strcmp) |
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EXPORT_SYMBOL_NOKASAN(strcmp)
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