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/* memchr implemented using NEON.
Copyright (C) 2011-2025 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>
/* For __ARM_NEON__ this file defines memchr. */
#ifndef __ARM_NEON__
# define memchr __memchr_neon
# undef libc_hidden_builtin_def
# define libc_hidden_builtin_def(a)
#endif
.arch armv7-a
.fpu neon
/* Arguments */
#define srcin r0
#define chrin r1
#define cntin r2
/* Retval */
#define result r0 /* Live range does not overlap with srcin */
/* Working registers */
#define src r1 /* Live range does not overlap with chrin */
#define tmp r3
#define synd r0 /* No overlap with srcin or result */
#define soff r12
/* Working NEON registers */
#define vrepchr q0
#define vdata0 q1
#define vdata0_0 d2 /* Lower half of vdata0 */
#define vdata0_1 d3 /* Upper half of vdata0 */
#define vdata1 q2
#define vdata1_0 d4 /* Lower half of vhas_chr0 */
#define vdata1_1 d5 /* Upper half of vhas_chr0 */
#define vrepmask q3
#define vrepmask0 d6
#define vrepmask1 d7
#define vend q4
#define vend0 d8
#define vend1 d9
/*
* Core algorithm:
*
* For each 32-byte chunk we calculate a 32-bit syndrome value, with one bit per
* byte. Each bit is set if the relevant byte matched the requested character
* and cleared otherwise. Since the bits in the syndrome reflect exactly the
* order in which things occur in the original string, counting trailing zeros
* allows to identify exactly which byte has matched.
*/
.thumb_func
.p2align 4,,15
ENTRY(memchr)
/* Use a simple loop if there are less than 8 bytes to search. */
cmp cntin, #7
bhi .Llargestr
and chrin, chrin, #0xff
.Lsmallstr:
subs cntin, cntin, #1
blo .Lnotfound /* Return not found if reached end. */
ldrb tmp, [srcin], #1
cmp tmp, chrin
bne .Lsmallstr /* Loop again if not found. */
/* Otherwise fixup address and return. */
sub result, srcin, #1
bx lr
.Llargestr:
vdup.8 vrepchr, chrin /* Duplicate char across all lanes. */
/*
* Magic constant 0x8040201008040201 allows us to identify which lane
* matches the requested byte.
*/
movw tmp, #0x0201
movt tmp, #0x0804
lsl soff, tmp, #4
vmov vrepmask0, tmp, soff
vmov vrepmask1, tmp, soff
/* Work with aligned 32-byte chunks */
bic src, srcin, #31
ands soff, srcin, #31
beq .Lloopintro /* Go straight to main loop if it's aligned. */
/*
* Input string is not 32-byte aligned. We calculate the syndrome
* value for the aligned 32 bytes block containing the first bytes
* and mask the irrelevant part.
*/
vld1.8 {vdata0, vdata1}, [src:256]!
sub tmp, soff, #32
adds cntin, cntin, tmp
vceq.i8 vdata0, vdata0, vrepchr
vceq.i8 vdata1, vdata1, vrepchr
vand vdata0, vdata0, vrepmask
vand vdata1, vdata1, vrepmask
vpadd.i8 vdata0_0, vdata0_0, vdata0_1
vpadd.i8 vdata1_0, vdata1_0, vdata1_1
vpadd.i8 vdata0_0, vdata0_0, vdata1_0
vpadd.i8 vdata0_0, vdata0_0, vdata0_0
vmov synd, vdata0_0[0]
/* Clear the soff lower bits */
lsr synd, synd, soff
lsl synd, synd, soff
/* The first block can also be the last */
bls .Lmasklast
/* Have we found something already? */
cbnz synd, .Ltail
.Lloopintro:
vpush {vend}
/* 264/265 correspond to d8/d9 for q4 */
cfi_adjust_cfa_offset (16)
cfi_rel_offset (264, 0)
cfi_rel_offset (265, 8)
.p2align 3,,7
.Lloop:
vld1.8 {vdata0, vdata1}, [src:256]!
subs cntin, cntin, #32
vceq.i8 vdata0, vdata0, vrepchr
vceq.i8 vdata1, vdata1, vrepchr
/* If we're out of data we finish regardless of the result. */
bls .Lend
/* Use a fast check for the termination condition. */
vorr vend, vdata0, vdata1
vorr vend0, vend0, vend1
vmov synd, tmp, vend0
orrs synd, synd, tmp
/* We're not out of data, loop if we haven't found the character. */
beq .Lloop
.Lend:
vpop {vend}
cfi_adjust_cfa_offset (-16)
cfi_restore (264)
cfi_restore (265)
/* Termination condition found, let's calculate the syndrome value. */
vand vdata0, vdata0, vrepmask
vand vdata1, vdata1, vrepmask
vpadd.i8 vdata0_0, vdata0_0, vdata0_1
vpadd.i8 vdata1_0, vdata1_0, vdata1_1
vpadd.i8 vdata0_0, vdata0_0, vdata1_0
vpadd.i8 vdata0_0, vdata0_0, vdata0_0
vmov synd, vdata0_0[0]
cbz synd, .Lnotfound
bhi .Ltail /* Uses the condition code from
subs cntin, cntin, #32 above. */
.Lmasklast:
/* Clear the (-cntin) upper bits to avoid out-of-bounds matches. */
neg cntin, cntin
lsl synd, synd, cntin
lsrs synd, synd, cntin
it eq
moveq src, #0 /* If no match, set src to 0 so the retval is 0. */
.Ltail:
/* Count the trailing zeros using bit reversing */
rbit synd, synd
/* Compensate the last post-increment */
sub src, src, #32
/* Count the leading zeros */
clz synd, synd
/* Compute the potential result and return */
add result, src, synd
bx lr
.Lnotfound:
/* Set result to NULL if not found and return */
mov result, #0
bx lr
END(memchr)
libc_hidden_builtin_def (memchr)
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