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152 lines
3.9 KiB
ArmAsm
152 lines
3.9 KiB
ArmAsm
/* strrchr: find the last instance of a character in a string.
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Copyright (C) 2014-2024 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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#include <sysdep.h>
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/* Assumptions:
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*
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* ARMv8-a, AArch64, Advanced SIMD.
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* MTE compatible.
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*/
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#define srcin x0
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#define chrin w1
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#define result x0
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#define src x2
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#define tmp x3
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#define synd x3
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#define shift x4
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#define src_match x4
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#define nul_match x5
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#define chr_match x6
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#define vrepchr v0
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#define vdata v1
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#define vhas_nul v2
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#define vhas_chr v3
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#define vrepmask v4
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#define vend v5
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#define dend d5
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/* Core algorithm.
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For each 16-byte chunk we calculate a 64-bit syndrome value, with
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four bits per byte (LSB is always in bits 0 and 1, for both big
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and little-endian systems). For each tuple, bits 0-1 are set if
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the relevant byte matched the requested character; bits 2-3 are set
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if the relevant byte matched the NUL end of string. */
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ENTRY (strrchr)
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PTR_ARG (0)
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bic src, srcin, 15
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dup vrepchr.16b, chrin
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movi vrepmask.16b, 0x33
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ld1 {vdata.16b}, [src]
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cmeq vhas_nul.16b, vdata.16b, 0
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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shrn vend.8b, vhas_nul.8h, 4
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lsl shift, srcin, 2
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fmov synd, dend
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lsr synd, synd, shift
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lsl synd, synd, shift
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ands nul_match, synd, 0xcccccccccccccccc
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bne L(tail)
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cbnz synd, L(loop2_start)
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.p2align 4
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L(loop1):
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ldr q1, [src, 16]
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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cbnz synd, L(loop1_end)
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ldr q1, [src, 32]!
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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cbz synd, L(loop1)
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sub src, src, 16
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L(loop1_end):
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add src, src, 16
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cmeq vhas_nul.16b, vdata.16b, 0
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#ifdef __AARCH64EB__
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bif vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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shrn vend.8b, vhas_nul.8h, 4
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fmov synd, dend
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rbit synd, synd
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#else
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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shrn vend.8b, vhas_nul.8h, 4
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fmov synd, dend
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#endif
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ands nul_match, synd, 0xcccccccccccccccc
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beq L(loop2_start)
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L(tail):
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sub nul_match, nul_match, 1
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and chr_match, synd, 0x3333333333333333
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ands chr_match, chr_match, nul_match
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add result, src, 15
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clz tmp, chr_match
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sub result, result, tmp, lsr 2
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csel result, result, xzr, ne
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ret
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.p2align 4
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nop
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nop
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L(loop2_start):
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add src, src, 16
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bic vrepmask.8h, 0xf0
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L(loop2):
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cmp synd, 0
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csel src_match, src, src_match, ne
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csel chr_match, synd, chr_match, ne
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ld1 {vdata.16b}, [src], 16
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cmeq vhas_nul.16b, vdata.16b, 0
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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tst synd, 0xcccccccccccccccc
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beq L(loop2)
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bic vhas_nul.8h, 0x0f, lsl 8
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addp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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and nul_match, synd, 0xcccccccccccccccc
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sub nul_match, nul_match, 1
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and tmp, synd, 0x3333333333333333
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ands tmp, tmp, nul_match
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csel chr_match, tmp, chr_match, ne
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csel src_match, src, src_match, ne
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sub src_match, src_match, 1
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clz tmp, chr_match
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sub result, src_match, tmp, lsr 2
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ret
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END(strrchr)
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weak_alias (strrchr, rindex)
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libc_hidden_builtin_def (strrchr)
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