| /* |
| * memchr - find a character in a memory zone |
| * |
| * Copyright (c) 2014, ARM Limited |
| * All rights Reserved. |
| * Copyright (c) 2014, Linaro Ltd. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are met: |
| * * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * * Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * * Neither the name of the company nor the names of its contributors |
| * may be used to endorse or promote products derived from this |
| * software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| |
| /* Assumptions: |
| * |
| * ARMv8-a, AArch64 |
| * Neon Available. |
| */ |
| |
| #include <private/bionic_asm.h> |
| |
| /* 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) |
| /* |
| * Magic constant 0x40100401 allows us to identify which lane matches |
| * the requested byte. |
| */ |
| cbz cntin, .Lzero_length |
| 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 .Lloop |
| |
| /* |
| * 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 .Lmasklast |
| /* Have we found something already? */ |
| cbnz synd, .Ltail |
| |
| .Lloop: |
| 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 .Lend |
| /* 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, .Lloop |
| |
| .Lend: |
| /* 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 .Ltail |
| |
| .Lmasklast: |
| /* 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 |
| |
| .Ltail: |
| /* 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 |
| |
| .Lzero_length: |
| mov result, xzr |
| ret |
| END(memchr) |
