/*
* strchrnul - find a character or nul in a string
*
* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
* See https://llvm.org/LICENSE.txt for license information.
* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
*/
/* Assumptions:
*
* ARMv8-a, AArch64
* Neon Available.
*/
#include "../asmdefs.h"
/* 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 v7
#define vend1 v16
/* 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). For each tuple, bit 0 is set iff
the relevant byte matched the requested character or 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. */
/* Locals and temporaries. */
ENTRY (__strchrnul_aarch64)
/* Magic constant 0x40100401 to allow us to identify which lane
matches the termination condition. */
mov wtmp2, #0x0401
movk wtmp2, #0x4010, lsl #16
dup vrepchr.16b, chrin
bic src, srcin, #31 /* Work with aligned 32-byte hunks. */
dup vrepmask.4s, wtmp2
ands tmp1, srcin, #31
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
orr vhas_chr1.16b, vhas_chr1.16b, vhas_nul1.16b
orr vhas_chr2.16b, vhas_chr2.16b, vhas_nul2.16b
and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
lsl tmp1, tmp1, #1
addp vend1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
mov tmp3, #~0
addp vend1.16b, vend1.16b, vend1.16b // 128->64
lsr tmp1, tmp3, tmp1
mov tmp3, vend1.d[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 vhas_chr1.16b, vhas_nul1.16b, vhas_chr1.16b
orr vhas_chr2.16b, vhas_nul2.16b, vhas_chr2.16b
orr vend1.16b, vhas_chr1.16b, vhas_chr2.16b
addp vend1.2d, vend1.2d, vend1.2d
mov tmp1, vend1.d[0]
cbz tmp1, L(loop)
/* Termination condition found. Now need to establish exactly why
we terminated. */
and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
addp vend1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
addp vend1.16b, vend1.16b, vend1.16b // 128->64
mov tmp1, vend1.d[0]
L(tail):
/* Count the trailing zeros, by bit reversing... */
rbit tmp1, tmp1
/* Re-bias source. */
sub src, src, #32
clz tmp1, tmp1 /* ... and counting the leading zeros. */
/* tmp1 is twice the offset into the fragment. */
add result, src, tmp1, lsr #1
ret
END (__strchrnul_aarch64)
Codebase Browser
llvm