1/* 2 strchr - find a character in a string 3 4 Copyright (c) 2014, ARM Limited 5 All rights Reserved. 6 Copyright (c) 2014, Linaro Ltd. 7 8 Redistribution and use in source and binary forms, with or without 9 modification, are permitted provided that the following conditions are met: 10 * Redistributions of source code must retain the above copyright 11 notice, this list of conditions and the following disclaimer. 12 * Redistributions in binary form must reproduce the above copyright 13 notice, this list of conditions and the following disclaimer in the 14 documentation and/or other materials provided with the distribution. 15 * Neither the name of the company nor the names of its contributors 16 may be used to endorse or promote products derived from this 17 software without specific prior written permission. 18 19 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 20 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 21 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 22 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 23 HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 24 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 25 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 26 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 27 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 28 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 29 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 30*/ 31 32/* Assumptions: 33 * 34 * ARMv8-a, AArch64 35 * Neon Available. 36 */ 37 38#include <private/bionic_asm.h> 39 40/* Arguments and results. */ 41#define srcin x0 42#define chrin w1 43 44#define result x0 45 46#define src x2 47#define tmp1 x3 48#define wtmp2 w4 49#define tmp3 x5 50 51#define vrepchr v0 52#define vdata1 v1 53#define vdata2 v2 54#define vhas_nul1 v3 55#define vhas_nul2 v4 56#define vhas_chr1 v5 57#define vhas_chr2 v6 58#define vrepmask_0 v7 59#define vrepmask_c v16 60#define vend1 v17 61#define vend2 v18 62 63/* Core algorithm. 64 65 For each 32-byte hunk we calculate a 64-bit syndrome value, with 66 two bits per byte (LSB is always in bits 0 and 1, for both big 67 and little-endian systems). For each tuple, bit 0 is set iff 68 the relevant byte matched the requested character; bit 1 is set 69 iff the relevant byte matched the NUL end of string (we trigger 70 off bit0 for the special case of looking for NUL). Since the bits 71 in the syndrome reflect exactly the order in which things occur 72 in the original string a count_trailing_zeros() operation will 73 identify exactly which byte is causing the termination, and why. */ 74 75/* Locals and temporaries. */ 76 77ENTRY(strchr) 78 /* Magic constant 0x40100401 to allow us to identify which lane 79 matches the requested byte. Magic constant 0x80200802 used 80 similarly for NUL termination. */ 81 mov wtmp2, #0x0401 82 movk wtmp2, #0x4010, lsl #16 83 dup vrepchr.16b, chrin 84 bic src, srcin, #31 /* Work with aligned 32-byte hunks. */ 85 dup vrepmask_c.4s, wtmp2 86 ands tmp1, srcin, #31 87 add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */ 88 b.eq .Lloop 89 90 /* Input string is not 32-byte aligned. Rather than forcing 91 the padding bytes to a safe value, we calculate the syndrome 92 for all the bytes, but then mask off those bits of the 93 syndrome that are related to the padding. */ 94 ld1 {vdata1.16b, vdata2.16b}, [src], #32 95 neg tmp1, tmp1 96 cmeq vhas_nul1.16b, vdata1.16b, #0 97 cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b 98 cmeq vhas_nul2.16b, vdata2.16b, #0 99 cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b 100 and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b 101 and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b 102 and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b 103 and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b 104 orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b 105 orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b 106 lsl tmp1, tmp1, #1 107 addp vend1.16b, vend1.16b, vend2.16b // 256->128 108 mov tmp3, #~0 109 addp vend1.16b, vend1.16b, vend2.16b // 128->64 110 lsr tmp1, tmp3, tmp1 111 112 mov tmp3, vend1.d[0] 113 bic tmp1, tmp3, tmp1 // Mask padding bits. 114 cbnz tmp1, .Ltail 115 116.Lloop: 117 ld1 {vdata1.16b, vdata2.16b}, [src], #32 118 cmeq vhas_nul1.16b, vdata1.16b, #0 119 cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b 120 cmeq vhas_nul2.16b, vdata2.16b, #0 121 cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b 122 /* Use a fast check for the termination condition. */ 123 orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b 124 orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b 125 orr vend1.16b, vend1.16b, vend2.16b 126 addp vend1.2d, vend1.2d, vend1.2d 127 mov tmp1, vend1.d[0] 128 cbz tmp1, .Lloop 129 130 /* Termination condition found. Now need to establish exactly why 131 we terminated. */ 132 and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b 133 and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b 134 and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b 135 and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b 136 orr vend1.16b, vhas_nul1.16b, vhas_chr1.16b 137 orr vend2.16b, vhas_nul2.16b, vhas_chr2.16b 138 addp vend1.16b, vend1.16b, vend2.16b // 256->128 139 addp vend1.16b, vend1.16b, vend2.16b // 128->64 140 141 mov tmp1, vend1.d[0] 142.Ltail: 143 /* Count the trailing zeros, by bit reversing... */ 144 rbit tmp1, tmp1 145 /* Re-bias source. */ 146 sub src, src, #32 147 clz tmp1, tmp1 /* And counting the leading zeros. */ 148 /* Tmp1 is even if the target charager was found first. Otherwise 149 we've found the end of string and we weren't looking for NUL. */ 150 tst tmp1, #1 151 add result, src, tmp1, lsr #1 152 csel result, result, xzr, eq 153 ret 154END(strchr) 155