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51541a2297
Simplify calculation of the mask using shrn. Unroll the main loop. Small strings are 20% faster on modern CPUs. Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
116 lines
3.1 KiB
ArmAsm
116 lines
3.1 KiB
ArmAsm
/* strchr - find a character in a string
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Copyright (C) 2014-2023 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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<https://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, Advanced SIMD.
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* MTE compatible.
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*/
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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 x1
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#define tmp2 x3
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#define vrepchr v0
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#define vdata v1
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#define qdata q1
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#define vhas_nul v2
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#define vhas_chr v3
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#define vrepmask v4
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#define vend v5
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#define dend d5
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/* Core algorithm.
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For each 16-byte chunk we calculate a 64-bit syndrome value with four bits
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per byte. Bits 0-1 are set if the relevant byte matched the requested
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character, bits 2-3 are set if the byte is NUL or matched. Count trailing
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zeroes gives the position of the matching byte if it is a multiple of 4.
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If it is not a multiple of 4, there was no match. */
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ENTRY (strchr)
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PTR_ARG (0)
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bic src, srcin, 15
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dup vrepchr.16b, chrin
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ld1 {vdata.16b}, [src]
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movi vrepmask.16b, 0x33
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cmeq vhas_nul.16b, vdata.16b, 0
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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lsl tmp2, srcin, 2
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shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
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fmov tmp1, dend
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lsr tmp1, tmp1, tmp2
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cbz tmp1, L(loop)
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rbit tmp1, tmp1
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clz tmp1, tmp1
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/* Tmp1 is an even multiple of 2 if the target character was
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found first. Otherwise we've found the end of string. */
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tst tmp1, 2
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add result, srcin, tmp1, lsr 2
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csel result, result, xzr, eq
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ret
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.p2align 4
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L(loop):
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ldr qdata, [src, 16]
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov tmp1, dend
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cbnz tmp1, L(end)
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ldr qdata, [src, 32]!
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov tmp1, dend
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cbz tmp1, L(loop)
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sub src, src, 16
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L(end):
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#ifdef __AARCH64EB__
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bif vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
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fmov tmp1, dend
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#else
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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shrn vend.8b, vhas_nul.8h, 4 /* 128->64 */
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fmov tmp1, dend
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rbit tmp1, tmp1
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#endif
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add src, src, 16
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clz tmp1, tmp1
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/* Tmp1 is a multiple of 4 if the target character was found. */
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tst tmp1, 2
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add result, src, tmp1, lsr 2
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csel result, result, xzr, eq
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ret
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END (strchr)
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libc_hidden_builtin_def (strchr)
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weak_alias (strchr, index)
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