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/*
* memchr - find a character in a memory zone
*
* Copyright (c) 2014, ARM Limited
* All rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of the company nor the names of its contributors
* may be used to endorse or promote products derived from this
* software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#if (defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED))
/* See memchr-stub.c */
#else
/* Assumptions:
*
* ARMv8-a, AArch64
* Neon Available.
*/
/* Arguments and results. */
#define srcin x0
#define chrin w1
#define cntin x2
#define result x0
#define src x3
#define tmp x4
#define wtmp2 w5
#define synd x6
#define soff x9
#define cntrem x10
#define vrepchr v0
#define vdata1 v1
#define vdata2 v2
#define vhas_chr1 v3
#define vhas_chr2 v4
#define vrepmask v5
#define vend v6
/*
* Core algorithm:
*
* For each 32-byte chunk we calculate a 64-bit syndrome value, with two bits
* per byte. For each tuple, bit 0 is set if the relevant byte matched the
* requested character and bit 1 is not used (faster than using a 32bit
* syndrome). 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.
*/
.macro def_fn f p2align=0
.text
.p2align \p2align
.global \f
.type \f, %function
\f:
.endm
def_fn memchr
/* Do not dereference srcin if no bytes to compare. */
cbz cntin, .Lzero_length
/*
* Magic constant 0x40100401 allows us to identify which lane matches
* the requested byte.
*/
mov wtmp2, #0x0401
movk wtmp2, #0x4010, lsl #16
dup vrepchr.16b, chrin
/* Work with aligned 32-byte chunks */
bic src, srcin, #31
dup vrepmask.4s, wtmp2
ands soff, srcin, #31
and cntrem, cntin, #31
b.eq .Lloop
/*
* 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.
*/
ld1 {vdata1.16b, vdata2.16b}, [src], #32
sub tmp, soff, #32
adds cntin, cntin, tmp
cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
addp vend.16b, vhas_chr1.16b, vhas_chr2.16b /* 256->128 */
addp vend.16b, vend.16b, vend.16b /* 128->64 */
mov synd, vend.2d[0]
/* Clear the soff*2 lower bits */
lsl tmp, soff, #1
lsr synd, synd, tmp
lsl synd, synd, tmp
/* The first block can also be the last */
b.ls .Lmasklast
/* Have we found something already? */
cbnz synd, .Ltail
.Lloop:
ld1 {vdata1.16b, vdata2.16b}, [src], #32
subs cntin, cntin, #32
cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
/* If we're out of data we finish regardless of the result */
b.ls .Lend
/* Use a fast check for the termination condition */
orr vend.16b, vhas_chr1.16b, vhas_chr2.16b
addp vend.2d, vend.2d, vend.2d
mov synd, vend.2d[0]
/* We're not out of data, loop if we haven't found the character */
cbz synd, .Lloop
.Lend:
/* Termination condition found, let's calculate the syndrome value */
and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
addp vend.16b, vhas_chr1.16b, vhas_chr2.16b /* 256->128 */
addp vend.16b, vend.16b, vend.16b /* 128->64 */
mov synd, vend.2d[0]
/* Only do the clear for the last possible block */
b.hi .Ltail
.Lmasklast:
/* Clear the (32 - ((cntrem + soff) % 32)) * 2 upper bits */
add tmp, cntrem, soff
and tmp, tmp, #31
sub tmp, tmp, #32
neg tmp, tmp, lsl #1
lsl synd, synd, tmp
lsr synd, synd, tmp
.Ltail:
/* Count the trailing zeros using bit reversing */
rbit synd, synd
/* Compensate the last post-increment */
sub src, src, #32
/* Check that we have found a character */
cmp synd, #0
/* And count the leading zeros */
clz synd, synd
/* Compute the potential result */
add result, src, synd, lsr #1
/* Select result or NULL */
csel result, xzr, result, eq
ret
.Lzero_length:
mov result, #0
ret
.size memchr, . - memchr
#endif
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