mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-31 06:51:11 +00:00
[AArch64] Add optimized strchr.
Implementation of strchr for AArch64. Speedups taken from micro-bench show the improvements relative to the standard C code. The use of LD1 means we have identical code for both big- and little-endian systems.
This commit is contained in:
Richard Earnshaw
Marcus Shawcroft
parent
4ba7a00fe3
commit
f940b96522
@ -1,3 +1,7 @@
|
||||
2014-06-19 Richard Earnshaw <rearnsha@arm.com>
|
||||
|
||||
* sysdeps/aarch64/strchr.S: New file.
|
||||
|
||||
2014-06-18 Joseph Myers <joseph@codesourcery.com>
|
||||
|
||||
[BZ #17022]
|
||||
|
||||
2
NEWS
2
NEWS
@ -22,6 +22,8 @@ Version 2.20
|
||||
16967, 16977, 16978, 16984, 16990, 16996, 17009, 17022, 17031, 17042,
|
||||
17048, 17058, 17062.
|
||||
|
||||
* Optimized strchr implementation for AArch64. Contributed by ARM Ltd.
|
||||
|
||||
* The minimum Linux kernel version that this version of the GNU C Library
|
||||
can be used with is 2.6.32.
|
||||
|
||||
|
||||
138
sysdeps/aarch64/strchr.S
Normal file
138
sysdeps/aarch64/strchr.S
Normal file
@ -0,0 +1,138 @@
|
||||
/* strchr - find a character in a string
|
||||
|
||||
Copyright (C) 2014 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
|
||||
<http://www.gnu.org/licenses/>. */
|
||||
|
||||
#include <sysdep.h>
|
||||
|
||||
/* Assumptions:
|
||||
*
|
||||
* ARMv8-a, AArch64
|
||||
*/
|
||||
|
||||
/* Arguments and results. */
|
||||
#define srcin x0
|
||||
#define chrin w1
|
||||
|
||||
#define result x0
|
||||
|
||||
#define src x2
|
||||
#define tmp1 x3
|
||||
#define wtmp2 w4
|
||||
#define tmp3 x5
|
||||
|
||||
#define vrepchr v0
|
||||
#define vdata1 v1
|
||||
#define vdata2 v2
|
||||
#define vhas_nul1 v3
|
||||
#define vhas_nul2 v4
|
||||
#define vhas_chr1 v5
|
||||
#define vhas_chr2 v6
|
||||
#define vrepmask_0 v7
|
||||
#define vrepmask_c v16
|
||||
#define vend1 v17
|
||||
#define vend2 v18
|
||||
|
||||
/* Core algorithm.
|
||||
For each 32-byte hunk we calculate a 64-bit syndrome value, with
|
||||
two bits per byte (LSB is always in bits 0 and 1, for both big
|
||||
and little-endian systems). Bit 0 is set iff the relevant byte
|
||||
matched the requested character. Bit 1 is set iff the
|
||||
relevant byte matched the NUL end of string (we trigger off bit0
|
||||
for the special case of looking for NUL). Since the bits
|
||||
in the syndrome reflect exactly the order in which things occur
|
||||
in the original string a count_trailing_zeros() operation will
|
||||
identify exactly which byte is causing the termination, and why. */
|
||||
|
||||
/* Locals and temporaries. */
|
||||
|
||||
ENTRY (strchr)
|
||||
mov wtmp2, #0x0401
|
||||
movk wtmp2, #0x4010, lsl #16
|
||||
dup vrepchr.16b, chrin
|
||||
bic src, srcin, #31
|
||||
dup vrepmask_c.4s, wtmp2
|
||||
ands tmp1, srcin, #31
|
||||
add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s // lsl #1
|
||||
b.eq L(loop)
|
||||
|
||||
/* Input string is not 32-byte aligned. Rather than forcing
|
||||
the padding bytes to a safe value, we calculate the syndrome
|
||||
for all the bytes, but then mask off those bits of the
|
||||
syndrome that are related to the padding. */
|
||||
ld1 {vdata1.16b, vdata2.16b}, [src], #32
|
||||
neg tmp1, tmp1
|
||||
cmeq vhas_nul1.16b, vdata1.16b, #0
|
||||
cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
|
||||
cmeq vhas_nul2.16b, vdata2.16b, #0
|
||||
cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
|
||||
and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
|
||||
and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
|
||||
and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
|
||||
and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
|
||||
orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b
|
||||
orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b
|
||||
lsl tmp1, tmp1, #1
|
||||
addp vend1.16b, vend1.16b, vend2.16b // 256->128
|
||||
mov tmp3, #~0
|
||||
addp vend1.16b, vend1.16b, vend2.16b // 128->64
|
||||
lsr tmp1, tmp3, tmp1
|
||||
|
||||
mov tmp3, vend1.2d[0]
|
||||
bic tmp1, tmp3, tmp1 // Mask padding bits.
|
||||
cbnz tmp1, L(tail)
|
||||
|
||||
L(loop):
|
||||
ld1 {vdata1.16b, vdata2.16b}, [src], #32
|
||||
cmeq vhas_nul1.16b, vdata1.16b, #0
|
||||
cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
|
||||
cmeq vhas_nul2.16b, vdata2.16b, #0
|
||||
cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
|
||||
/* Use a fast check for the termination condition. */
|
||||
orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b
|
||||
orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b
|
||||
orr vend1.16b, vend1.16b, vend2.16b
|
||||
addp vend1.2d, vend1.2d, vend1.2d
|
||||
mov tmp1, vend1.2d[0]
|
||||
cbz tmp1, L(loop)
|
||||
|
||||
/* Termination condition found. Now need to establish exactly why
|
||||
we terminated. */
|
||||
and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
|
||||
and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
|
||||
and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
|
||||
and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
|
||||
orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b
|
||||
orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b
|
||||
addp vend1.16b, vend1.16b, vend2.16b // 256->128
|
||||
addp vend1.16b, vend1.16b, vend2.16b // 128->64
|
||||
|
||||
mov tmp1, vend1.2d[0]
|
||||
L(tail):
|
||||
sub src, src, #32
|
||||
rbit tmp1, tmp1
|
||||
clz tmp1, tmp1
|
||||
/* Tmp1 is even if the target charager was found first. Otherwise
|
||||
we've found the end of string and we weren't looking for NUL. */
|
||||
tst tmp1, #1
|
||||
add result, src, tmp1, lsr #1
|
||||
csel result, result, xzr, eq
|
||||
ret
|
||||
END (strchr)
|
||||
libc_hidden_builtin_def (strchr)
|
||||
weak_alias (strchr, index)
|
||||
Loading…
Reference in New Issue
Block a user