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149 lines
4.8 KiB
149 lines
4.8 KiB
4 months ago
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/*
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* strrchr - find last position of a character in a string.
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*
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* Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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* See https://llvm.org/LICENSE.txt for license information.
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* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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*/
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/* Assumptions:
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*
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* ARMv8-a, AArch64
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* Neon Available.
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*/
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#include "../asmdefs.h"
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/* Arguments and results. */
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#define srcin x0
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#define chrin w1
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#define result x0
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#define src x2
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#define tmp1 x3
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#define wtmp2 w4
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#define tmp3 x5
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#define src_match x6
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#define src_offset x7
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#define const_m1 x8
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#define tmp4 x9
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#define nul_match x10
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#define chr_match x11
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#define vrepchr v0
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#define vdata1 v1
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#define vdata2 v2
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#define vhas_nul1 v3
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#define vhas_nul2 v4
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#define vhas_chr1 v5
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#define vhas_chr2 v6
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#define vrepmask_0 v7
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#define vrepmask_c v16
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#define vend1 v17
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#define vend2 v18
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/* Core algorithm.
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For each 32-byte hunk we calculate a 64-bit syndrome value, with
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two bits per byte (LSB is always in bits 0 and 1, for both big
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and little-endian systems). For each tuple, bit 0 is set iff
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the relevant byte matched the requested character; bit 1 is set
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iff the relevant byte matched the NUL end of string (we trigger
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off bit0 for the special case of looking for NUL). Since the bits
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in the syndrome reflect exactly the order in which things occur
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in the original string a count_trailing_zeros() operation will
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identify exactly which byte is causing the termination, and why. */
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ENTRY (__strrchr_aarch64)
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/* Magic constant 0x40100401 to allow us to identify which lane
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matches the requested byte. Magic constant 0x80200802 used
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similarly for NUL termination. */
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mov wtmp2, #0x0401
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movk wtmp2, #0x4010, lsl #16
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dup vrepchr.16b, chrin
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bic src, srcin, #31 /* Work with aligned 32-byte hunks. */
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dup vrepmask_c.4s, wtmp2
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mov src_offset, #0
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ands tmp1, srcin, #31
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add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */
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b.eq L(aligned)
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/* Input string is not 32-byte aligned. Rather than forcing
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the padding bytes to a safe value, we calculate the syndrome
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for all the bytes, but then mask off those bits of the
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syndrome that are related to the padding. */
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ld1 {vdata1.16b, vdata2.16b}, [src], #32
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neg tmp1, tmp1
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cmeq vhas_nul1.16b, vdata1.16b, #0
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cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
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cmeq vhas_nul2.16b, vdata2.16b, #0
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cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
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and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
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and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b // 128->64
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
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mov nul_match, vhas_nul1.d[0]
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lsl tmp1, tmp1, #1
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mov const_m1, #~0
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mov chr_match, vhas_chr1.d[0]
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lsr tmp3, const_m1, tmp1
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bic nul_match, nul_match, tmp3 // Mask padding bits.
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bic chr_match, chr_match, tmp3 // Mask padding bits.
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cbnz nul_match, L(tail)
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L(loop):
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cmp chr_match, #0
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csel src_match, src, src_match, ne
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csel src_offset, chr_match, src_offset, ne
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L(aligned):
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ld1 {vdata1.16b, vdata2.16b}, [src], #32
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cmeq vhas_nul1.16b, vdata1.16b, #0
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cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
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cmeq vhas_nul2.16b, vdata2.16b, #0
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cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
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addp vend1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
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addp vend1.16b, vend1.16b, vend1.16b // 128->64
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
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mov nul_match, vend1.d[0]
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mov chr_match, vhas_chr1.d[0]
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cbz nul_match, L(loop)
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and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
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and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b
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mov nul_match, vhas_nul1.d[0]
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L(tail):
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/* Work out exactly where the string ends. */
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sub tmp4, nul_match, #1
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eor tmp4, tmp4, nul_match
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ands chr_match, chr_match, tmp4
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/* And pick the values corresponding to the last match. */
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csel src_match, src, src_match, ne
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csel src_offset, chr_match, src_offset, ne
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/* Count down from the top of the syndrome to find the last match. */
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clz tmp3, src_offset
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/* Src_match points beyond the word containing the match, so we can
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simply subtract half the bit-offset into the syndrome. Because
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we are counting down, we need to go back one more character. */
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add tmp3, tmp3, #2
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sub result, src_match, tmp3, lsr #1
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/* But if the syndrome shows no match was found, then return NULL. */
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cmp src_offset, #0
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csel result, result, xzr, ne
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ret
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END (__strrchr_aarch64)
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