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