| /* memchr - find a character in a memory zone |
| |
| Copyright (C) 2015-2018 Free Software Foundation, Inc. |
| |
| This file is part of the GNU C Library. |
| |
| The GNU C Library is free software; you can redistribute it and/or |
| modify it under the terms of the GNU Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 of the License, or (at your option) any later version. |
| |
| The GNU C Library is distributed in the hope that it will be useful, |
| but WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library. If not, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include <sysdep.h> |
| |
| /* Assumptions: |
| * |
| * ARMv8-a, AArch64 |
| * Neon Available. |
| */ |
| |
| /* Arguments and results. */ |
| #define srcin x0 |
| #define chrin w1 |
| #define cntin x2 |
| |
| #define result x0 |
| |
| #define src x3 |
| #define tmp x4 |
| #define wtmp2 w5 |
| #define synd x6 |
| #define soff x9 |
| #define cntrem x10 |
| |
| #define vrepchr v0 |
| #define vdata1 v1 |
| #define vdata2 v2 |
| #define vhas_chr1 v3 |
| #define vhas_chr2 v4 |
| #define vrepmask v5 |
| #define vend v6 |
| |
| /* |
| * Core algorithm: |
| * |
| * For each 32-byte chunk we calculate a 64-bit syndrome value, with two bits |
| * per byte. For each tuple, bit 0 is set if the relevant byte matched the |
| * requested character and bit 1 is not used (faster than using a 32bit |
| * syndrome). Since the bits in the syndrome reflect exactly the order in which |
| * things occur in the original string, counting trailing zeros allows to |
| * identify exactly which byte has matched. |
| */ |
| |
| ENTRY (__memchr) |
| /* Do not dereference srcin if no bytes to compare. */ |
| cbz cntin, L(zero_length) |
| /* |
| * Magic constant 0x40100401 allows us to identify which lane matches |
| * the requested byte. |
| */ |
| mov wtmp2, #0x0401 |
| movk wtmp2, #0x4010, lsl #16 |
| dup vrepchr.16b, chrin |
| /* Work with aligned 32-byte chunks */ |
| bic src, srcin, #31 |
| dup vrepmask.4s, wtmp2 |
| ands soff, srcin, #31 |
| and cntrem, cntin, #31 |
| b.eq L(loop) |
| |
| /* |
| * Input string is not 32-byte aligned. We calculate the syndrome |
| * value for the aligned 32 bytes block containing the first bytes |
| * and mask the irrelevant part. |
| */ |
| |
| ld1 {vdata1.16b, vdata2.16b}, [src], #32 |
| sub tmp, soff, #32 |
| adds cntin, cntin, tmp |
| cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b |
| cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b |
| and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b |
| and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b |
| addp vend.16b, vhas_chr1.16b, vhas_chr2.16b /* 256->128 */ |
| addp vend.16b, vend.16b, vend.16b /* 128->64 */ |
| mov synd, vend.d[0] |
| /* Clear the soff*2 lower bits */ |
| lsl tmp, soff, #1 |
| lsr synd, synd, tmp |
| lsl synd, synd, tmp |
| /* The first block can also be the last */ |
| b.ls L(masklast) |
| /* Have we found something already? */ |
| cbnz synd, L(tail) |
| |
| L(loop): |
| ld1 {vdata1.16b, vdata2.16b}, [src], #32 |
| subs cntin, cntin, #32 |
| cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b |
| cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b |
| /* If we're out of data we finish regardless of the result */ |
| b.ls L(end) |
| /* Use a fast check for the termination condition */ |
| orr vend.16b, vhas_chr1.16b, vhas_chr2.16b |
| addp vend.2d, vend.2d, vend.2d |
| mov synd, vend.d[0] |
| /* We're not out of data, loop if we haven't found the character */ |
| cbz synd, L(loop) |
| |
| L(end): |
| /* Termination condition found, let's calculate the syndrome value */ |
| and vhas_chr1.16b, vhas_chr1.16b, vrepmask.16b |
| and vhas_chr2.16b, vhas_chr2.16b, vrepmask.16b |
| addp vend.16b, vhas_chr1.16b, vhas_chr2.16b /* 256->128 */ |
| addp vend.16b, vend.16b, vend.16b /* 128->64 */ |
| mov synd, vend.d[0] |
| /* Only do the clear for the last possible block */ |
| b.hi L(tail) |
| |
| L(masklast): |
| /* Clear the (32 - ((cntrem + soff) % 32)) * 2 upper bits */ |
| add tmp, cntrem, soff |
| and tmp, tmp, #31 |
| sub tmp, tmp, #32 |
| neg tmp, tmp, lsl #1 |
| lsl synd, synd, tmp |
| lsr synd, synd, tmp |
| |
| L(tail): |
| /* Count the trailing zeros using bit reversing */ |
| rbit synd, synd |
| /* Compensate the last post-increment */ |
| sub src, src, #32 |
| /* Check that we have found a character */ |
| cmp synd, #0 |
| /* And count the leading zeros */ |
| clz synd, synd |
| /* Compute the potential result */ |
| add result, src, synd, lsr #1 |
| /* Select result or NULL */ |
| csel result, xzr, result, eq |
| ret |
| |
| L(zero_length): |
| mov result, #0 |
| ret |
| END (__memchr) |
| weak_alias (__memchr, memchr) |
| libc_hidden_builtin_def (memchr) |