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/*
* strchrnul - find a character or nul in a string
*
* Copyright (c) 2020-2022, Arm Limited.
* SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception
*/
/* Assumptions:
*
* ARMv8-a, AArch64, Advanced SIMD.
* MTE compatible.
*/
#include "asmdefs.h"
#define srcin x0
#define chrin w1
#define result x0
#define src x2
#define tmp1 x1
#define tmp2 x3
#define vrepchr v0
#define vdata v1
#define qdata q1
#define vhas_nul v2
#define vhas_chr v3
#define vend v4
#define dend d4
/*
Core algorithm:
For each 16-byte chunk we calculate a 64-bit nibble mask value with four bits
per byte. We take 4 bits of every comparison byte with shift right and narrow
by 4 instruction. Since the bits in the nibble mask reflect the order in
which things occur in the original string, counting leading zeros identifies
exactly which byte matched. */
ENTRY (__strchrnul_aarch64_mte)
PTR_ARG (0)
bic src, srcin, 15
dup vrepchr.16b, chrin
ld1 {vdata.16b}, [src]
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
cmhs vhas_chr.16b, vhas_chr.16b, vdata.16b
lsl tmp2, srcin, 2
shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
fmov tmp1, dend
lsr tmp1, tmp1, tmp2 /* Mask padding bits. */
cbz tmp1, L(loop)
rbit tmp1, tmp1
clz tmp1, tmp1
add result, srcin, tmp1, lsr 2
ret
.p2align 4
L(loop):
ldr qdata, [src, 16]
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
cmhs vhas_chr.16b, vhas_chr.16b, vdata.16b
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b
fmov tmp1, dend
cbnz tmp1, L(end)
ldr qdata, [src, 32]!
cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
cmhs vhas_chr.16b, vhas_chr.16b, vdata.16b
umaxp vend.16b, vhas_chr.16b, vhas_chr.16b
fmov tmp1, dend
cbz tmp1, L(loop)
sub src, src, 16
L(end):
shrn vend.8b, vhas_chr.8h, 4 /* 128->64 */
add src, src, 16
fmov tmp1, dend
#ifndef __AARCH64EB__
rbit tmp1, tmp1
#endif
clz tmp1, tmp1
add result, src, tmp1, lsr 2
ret
END (__strchrnul_aarch64_mte)
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