/*
* strrchr - find last position of a character 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 src_match x6
#define src_offset x7
#define const_m1 x8
#define tmp4 x9
#define nul_match x10
#define chr_match x11
#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). For each tuple, 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. */
ENTRY (__strrchr_aarch64)
/* Magic constant 0x40100401 to allow us to identify which lane
matches the requested byte. Magic constant 0x80200802 used
similarly for NUL termination. */
mov wtmp2, #0x0401
movk wtmp2, #0x4010, lsl #16
dup vrepchr.16b, chrin
bic src, srcin, #31 /* Work with aligned 32-byte hunks. */
dup vrepmask_c.4s, wtmp2
mov src_offset, #0
ands tmp1, srcin, #31
add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */
b.eq L(aligned)
/* 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_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b // 128->64
addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
mov nul_match, vhas_nul1.d[0]
lsl tmp1, tmp1, #1
mov const_m1, #~0
mov chr_match, vhas_chr1.d[0]
lsr tmp3, const_m1, tmp1
bic nul_match, nul_match, tmp3 // Mask padding bits.
bic chr_match, chr_match, tmp3 // Mask padding bits.
cbnz nul_match, L(tail)
L(loop):
cmp chr_match, #0
csel src_match, src, src_match, ne
csel src_offset, chr_match, src_offset, ne
L(aligned):
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
addp vend1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
addp vend1.16b, vend1.16b, vend1.16b // 128->64
addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
mov nul_match, vend1.d[0]
mov chr_match, vhas_chr1.d[0]
cbz nul_match, L(loop)
and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b
addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b
mov nul_match, vhas_nul1.d[0]
L(tail):
/* Work out exactly where the string ends. */
sub tmp4, nul_match, #1
eor tmp4, tmp4, nul_match
ands chr_match, chr_match, tmp4
/* And pick the values corresponding to the last match. */
csel src_match, src, src_match, ne
csel src_offset, chr_match, src_offset, ne
/* Count down from the top of the syndrome to find the last match. */
clz tmp3, src_offset
/* Src_match points beyond the word containing the match, so we can
simply subtract half the bit-offset into the syndrome. Because
we are counting down, we need to go back one more character. */
add tmp3, tmp3, #2
sub result, src_match, tmp3, lsr #1
/* But if the syndrome shows no match was found, then return NULL. */
cmp src_offset, #0
csel result, result, xzr, ne
ret
END (__strrchr_aarch64)
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