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/*
* strnlen - calculate the length of a string with limit.
*
* Copyright (c) 2020, Arm Limited.
* SPDX-License-Identifier: MIT
*/
/* Assumptions:
*
* ARMv8-a, AArch64, Advanced SIMD.
* MTE compatible.
*/
#include "../asmdefs.h"
#define srcin x0
#define cntin x1
#define result x0
#define src x2
#define synd x3
#define shift x4
#define wtmp w4
#define tmp x4
#define cntrem x5
#define qdata q0
#define vdata v0
#define vhas_chr v1
#define vrepmask v2
#define vend v3
#define dend d3
/*
Core algorithm:
For each 16-byte chunk we calculate a 64-bit syndrome value with four bits
per byte. For even bytes, bits 0-3 are set if the relevant byte matched the
requested character or the byte is NUL. Bits 4-7 must be zero. Bits 4-7 are
set likewise for odd bytes so that adjacent bytes can be merged. Since the
bits in the syndrome reflect the order in which things occur in the original
string, counting trailing zeros identifies exactly which byte matched. */
ENTRY (__strnlen_aarch64)
PTR_ARG (0)
SIZE_ARG (1)
bic src, srcin, 15
mov wtmp, 0xf00f
cbz cntin, L(nomatch)
ld1 {vdata.16b}, [src], 16
dup vrepmask.8h, wtmp
cmeq vhas_chr.16b, vdata.16b, 0
lsl shift, srcin, 2
and vhas_chr.16b, vhas_chr.16b, vrepmask.16b
addp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
lsr synd, synd, shift
cbz synd, L(start_loop)
L(finish):
rbit synd, synd
clz synd, synd
lsr result, synd, 2
cmp cntin, result
csel result, cntin, result, ls
ret
L(start_loop):
sub tmp, src, srcin
subs cntrem, cntin, tmp
b.ls L(nomatch)
/* Make sure that it won't overread by a 16-byte chunk */
add tmp, cntrem, 15
tbnz tmp, 4, L(loop32_2)
.p2align 5
L(loop32):
ldr qdata, [src], 16
cmeq vhas_chr.16b, vdata.16b, 0
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbnz synd, L(end)
L(loop32_2):
ldr qdata, [src], 16
subs cntrem, cntrem, 32
cmeq vhas_chr.16b, vdata.16b, 0
b.ls L(end)
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
fmov synd, dend
cbz synd, L(loop32)
L(end):
and vhas_chr.16b, vhas_chr.16b, vrepmask.16b
addp vend.16b, vhas_chr.16b, vhas_chr.16b /* 128->64 */
sub src, src, 16
mov synd, vend.d[0]
sub result, src, srcin
#ifndef __AARCH64EB__
rbit synd, synd
#endif
clz synd, synd
add result, result, synd, lsr 2
cmp cntin, result
csel result, cntin, result, ls
ret
L(nomatch):
mov result, cntin
ret
END (__strnlen_aarch64)
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