201 lines
4.7 KiB
ArmAsm
201 lines
4.7 KiB
ArmAsm
/* Copyright (C) 2012-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<https://www.gnu.org/licenses/>. */
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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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#include <sysdep.h>
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#define REP8_01 0x0101010101010101
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#define REP8_7f 0x7f7f7f7f7f7f7f7f
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/* Parameters and result. */
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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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/* Internal variables. */
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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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ENTRY(strcmp)
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PTR_ARG (0)
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PTR_ARG (1)
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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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END(strcmp)
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libc_hidden_builtin_def (strcmp)
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