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/*
* strlen - calculate the length of a string.
*
* Copyright (c) 2020, Arm Limited.
* SPDX-License-Identifier: MIT
*/
/* Assumptions:
*
* ARMv8-a, AArch64, Advanced SIMD.
* MTE compatible.
*/
#include "../asmdefs.h"
#define srcin x0
#define result x0
#define src x1
#define synd x2
#define tmp x3
#define wtmp w3
#define shift x4
#define data q0
#define vdata v0
#define vhas_nul 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 (__strlen_aarch64_mte)
PTR_ARG (0)
bic src, srcin, 15
mov wtmp, 0xf00f
ld1 {vdata.16b}, [src]
dup vrepmask.8h, wtmp
cmeq vhas_nul.16b, vdata.16b, 0
lsl shift, srcin, 2
and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */
fmov synd, dend
lsr synd, synd, shift
cbz synd, L(loop)
rbit synd, synd
clz result, synd
lsr result, result, 2
ret
.p2align 5
L(loop):
ldr data, [src, 16]!
cmeq vhas_nul.16b, vdata.16b, 0
umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
fmov synd, dend
cbz synd, L(loop)
and vhas_nul.16b, vhas_nul.16b, vrepmask.16b
addp vend.16b, vhas_nul.16b, vhas_nul.16b /* 128->64 */
sub result, src, srcin
fmov synd, dend
#ifndef __AARCH64EB__
rbit synd, synd
#endif
clz tmp, synd
add result, result, tmp, lsr 2
ret
END (__strlen_aarch64_mte)
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