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Here is an optimized implementation of __strchrnul. The simplification that we don't have to track precisely why the loop terminates (match or end-of-string) means we have to do less work in both setup and the core inner loop. That means this should never be slower than strchr. As with strchr, the use of LD1 means we do not need different versions for big-/little-endian.
131 lines
4.1 KiB
ArmAsm
131 lines
4.1 KiB
ArmAsm
/* strchrnul - find a character or nul in a string
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Copyright (C) 2014 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library. If not, see
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<http://www.gnu.org/licenses/>. */
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#include <sysdep.h>
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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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/* 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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/* Locals and temporaries. */
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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 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 v15
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#define vend1 v16
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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 or nul. Since the
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bits 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. */
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ENTRY (__strchrnul)
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/* Magic constant 0x40100401 to allow us to identify which lane
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matches the termination condition. */
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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.4s, wtmp2
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ands tmp1, srcin, #31
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b.eq L(loop)
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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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orr vhas_chr1.16b, vhas_chr1.16b, vhas_nul1.16b
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orr vhas_chr2.16b, vhas_chr2.16b, vhas_nul2.16b
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
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lsl tmp1, tmp1, #1
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addp vend1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
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mov tmp3, #~0
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addp vend1.16b, vend1.16b, vend1.16b // 128->64
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lsr tmp1, tmp3, tmp1
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mov tmp3, vend1.2d[0]
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bic tmp1, tmp3, tmp1 // Mask padding bits.
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cbnz tmp1, L(tail)
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L(loop):
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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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/* Use a fast check for the termination condition. */
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orr vhas_chr1.16b, vhas_nul1.16b, vhas_chr1.16b
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orr vhas_chr2.16b, vhas_nul2.16b, vhas_chr2.16b
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orr vend1.16b, vhas_chr1.16b, vhas_chr2.16b
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addp vend1.2d, vend1.2d, vend1.2d
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mov tmp1, vend1.2d[0]
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cbz tmp1, L(loop)
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/* Termination condition found. Now need to establish exactly why
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we terminated. */
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b
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addp vend1.16b, 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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mov tmp1, vend1.2d[0]
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L(tail):
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/* Count the trailing zeros, by bit reversing... */
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rbit tmp1, tmp1
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/* Re-bias source. */
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sub src, src, #32
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clz tmp1, tmp1 /* ... and counting the leading zeros. */
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/* tmp1 is twice the offset into the fragment. */
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add result, src, tmp1, lsr #1
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ret
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END(__strchrnul)
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weak_alias (__strchrnul, strchrnul)
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