mirror of
git://sourceware.org/git/glibc.git
synced 2024-11-21 01:12:26 +08:00
166 lines
4.6 KiB
ArmAsm
166 lines
4.6 KiB
ArmAsm
/* memrchr - find the last occurrence of a byte in a memory block
|
|
|
|
Copyright (C) 2015-2020 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
|
|
* Neon Available.
|
|
*/
|
|
|
|
/* Arguments and results. */
|
|
#define srcin x0
|
|
#define chrin w1
|
|
#define cntin x2
|
|
|
|
#define seek_dstin x11
|
|
#define seek_dst x12
|
|
#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.
|
|
*/
|
|
|
|
ENTRY (__memrchr)
|
|
/* Do not dereference srcin if no bytes to compare. */
|
|
cbz cntin, L(zero_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 */
|
|
add seek_dstin, cntin, srcin
|
|
add tmp, seek_dstin, #31
|
|
bic seek_dst, tmp, #31
|
|
dup vrepmask.4s, wtmp2
|
|
ands soff, seek_dstin, #31
|
|
mov tmp, #32
|
|
sub soff,tmp,soff
|
|
and cntrem, cntin, #31
|
|
b.eq L(loop)
|
|
|
|
/*
|
|
* 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.
|
|
*/
|
|
|
|
sub seek_dst, seek_dst, #32
|
|
ld1 {vdata1.16b, vdata2.16b}, [seek_dst]
|
|
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 (32-soff)*2 upper bits */
|
|
lsl tmp, soff, #1
|
|
lsl synd, synd, tmp
|
|
lsr synd, synd, tmp
|
|
/* The first block can also be the last */
|
|
b.ls L(masklast)
|
|
/* Have we found something already? */
|
|
cbnz synd, L(tail)
|
|
|
|
L(loop):
|
|
sub seek_dst, seek_dst, #32
|
|
ld1 {vdata1.16b, vdata2.16b}, [seek_dst]
|
|
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 L(end)
|
|
/* 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, L(loop)
|
|
|
|
L(end):
|
|
/* 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 L(tail)
|
|
|
|
L(masklast):
|
|
/* Clear the (32 - ((cntrem + (32-soff)) % 32)) * 2 lower bits */
|
|
add tmp, cntrem, soff
|
|
and tmp, tmp, #31
|
|
sub tmp, tmp, #32
|
|
neg tmp, tmp, lsl #1
|
|
lsr synd, synd, tmp
|
|
lsl synd, synd, tmp
|
|
|
|
L(tail):
|
|
/* Compensate the last post-increment*/
|
|
add seek_dst, seek_dst, #32
|
|
/* Check that we have found a character */
|
|
cmp synd, #0
|
|
/* And count the leading zeros */
|
|
clz synd, synd
|
|
/* Compute the potential result */
|
|
sub result, seek_dst, synd, lsr #1
|
|
sub result, result, #1
|
|
/* Select result or NULL */
|
|
csel result, xzr, result, eq
|
|
ret
|
|
|
|
L(zero_length):
|
|
mov result, #0
|
|
ret
|
|
END (__memrchr)
|
|
weak_alias (__memrchr, memrchr)
|
|
libc_hidden_builtin_def (memrchr)
|