1 /*- 2 * Copyright (c) 2013 The NetBSD Foundation, Inc. 3 * All rights reserved. 4 * 5 * This code is derived from software contributed to The NetBSD Foundation 6 * by Matt Thomas of 3am Software Foundry. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 18 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 19 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 20 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 21 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 22 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 23 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 24 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 25 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 26 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 27 * POSSIBILITY OF SUCH DAMAGE. 28 */ 29 30 #include <machine/asm.h> 31 32 RCSID("$NetBSD: strchr_arm.S,v 1.8 2013/08/19 17:50:04 matt Exp $") 33 34 #if defined(__thumb__) && !defined(_ARM_ARCH_T2) 35 #error Only Thumb2 or ARM supported 36 #endif 37 38 #ifdef __ARMEL__ 39 #define BYTE0 0x000000ff 40 #define BYTE1 0x0000ff00 41 #define BYTE2 0x00ff0000 42 #define BYTE3 0xff000000 43 #define lshi lsl 44 #define lshis lsls 45 #else 46 #define BYTE0 0xff000000 47 #define BYTE1 0x00ff0000 48 #define BYTE2 0x0000ff00 49 #define BYTE3 0x000000ff 50 #define lshi lsr 51 #define lshis lsrs 52 #endif 53 54 .text 55 ENTRY(strchr) 56 and r2, r1, #0xff /* restrict to byte value */ 57 1: tst r0, #3 /* test for word alignment */ 58 beq .Lpre_main_loop /* finally word aligned */ 59 ldrb r3, [r0], #1 /* load a byte */ 60 cmp r3, r2 /* is it a match? */ 61 beq 2f /* yes, return current ptr - 1 */ 62 cmp r3, #0 /* no, was it 0? */ 63 bne 1b /* no, try next byte */ 64 movs r0, #0 /* yes, set return value to NULL */ 65 RET /* return */ 66 2: subs r0, r0, #1 /* back up by one */ 67 RET /* return */ 68 .Lpre_main_loop: 69 #if defined(_ARM_ARCH_7) 70 movw ip, #0xfefe /* magic constant; 254 in each byte */ 71 movt ip, #0xfefe /* magic constant; 254 in each byte */ 72 #elif defined(_ARM_ARCH_6) 73 mov ip, #0xfe /* put 254 in low byte */ 74 orr ip, ip, ip, lsl #8 /* move to next byte */ 75 orr ip, ip, ip, lsl #16 /* move to next halfword */ 76 #endif /* _ARM_ARCH_6 */ 77 orr r2, r2, r2, lsl #8 /* move to next byte */ 78 orr r2, r2, r2, lsl #16 /* move to next halfword */ 79 .Lmain_loop: 80 ldr r3, [r0], #4 /* load next word */ 81 #if defined(_ARM_ARCH_6) 82 /* 83 * Add 254 to each byte using the UQADD8 (unsigned saturating add 8) 84 * instruction. For every non-NUL byte, the result for that byte will 85 * become 255. For NUL, it will be 254. When we complement the 86 * result, if the result is non-0 then we must have encountered a NUL. 87 */ 88 uqadd8 r1, r3, ip /* NUL detection happens here */ 89 eors r3, r3, r2 /* xor to clear each lane */ 90 uqadd8 r3, r3, ip /* char detection happens here */ 91 ands r3, r3, r1 /* merge results */ 92 mvns r3, r3 /* is the complement non-0? */ 93 beq .Lmain_loop /* no, then keep going */ 94 95 /* 96 * We've encountered a NUL or a match but we don't know which happened 97 * first. 98 */ 99 #if defined(__thumb__) && defined(_ARM_ARCH_T2) 100 cbz r2, .Lfind_match /* searching for NUL? yes, find it */ 101 #else 102 cmp r2, #0 /* searching for NUL? */ 103 beq .Lfind_match /* yes, find the match */ 104 #endif 105 mvns r1, r1 /* did we encounter a NUL? */ 106 beq .Lfind_match /* no, find the match */ 107 bics r3, r3, r1 /* clear match for the NUL(s) */ 108 beq .Lnomatch /* any left set? if not, no match */ 109 lshis r1, r1, #8 /* replicate NUL bit to other bytes */ 110 #ifdef __thumb__ 111 itt ne 112 #endif 113 orrne r1, r1, r1, lshi #8 /* replicate NUL bit to other bytes */ 114 orrne r1, r1, r1, lshi #8 /* replicate NUL bit to other bytes */ 115 bics r3, r3, r1 /* clear any match bits after the NUL */ 116 beq .Lnomatch /* any left set? if not, no match */ 117 .Lfind_match: 118 #ifdef __ARMEL__ 119 rev r3, r3 /* we want this in BE for the CLZ */ 120 #endif 121 clz r3, r3 /* count how many leading zeros */ 122 add r0, r0, r3, lsr #3 /* divide that by 8 and add to count */ 123 subs r0, r0, #4 /* compensate for the post-inc */ 124 RET 125 .Lnomatch: 126 movs r0, #0 127 RET 128 #else 129 /* 130 * No fancy shortcuts so just test each byte lane for a NUL. 131 * (other tests for NULs in a word take more instructions/cycles). 132 */ 133 eor r1, r3, r2 /* xor .. */ 134 tst r3, #BYTE0 /* is this byte NUL? */ 135 tstne r1, #BYTE0 /* no, does this byte match? */ 136 tstne r3, #BYTE1 /* no, is this byte NUL? */ 137 tstne r1, #BYTE1 /* no, does this byte match? */ 138 tstne r3, #BYTE2 /* no, is this byte NUL? */ 139 tstne r1, #BYTE2 /* no, does this byte match? */ 140 tstne r3, #BYTE3 /* no, is this byte NUL? */ 141 tstne r1, #BYTE3 /* no, does this byte match? */ 142 bne .Lmain_loop 143 144 sub r2, r0, #4 /* un post-inc */ 145 mov r0, #0 /* assume no match */ 146 147 tst r1, #BYTE0 /* does this byte match? */ 148 moveq r0, r2 /* yes, point to it */ 149 RETc(eq) /* and return */ 150 tst r3, #BYTE0 /* is this byte NUL? */ 151 RETc(eq) /* yes, return NULL */ 152 153 tst r1, #BYTE1 /* does this byte match? */ 154 addeq r0, r2, #1 /* yes, point to it */ 155 RETc(eq) /* and return */ 156 tst r3, #BYTE1 /* is this byte NUL? */ 157 RETc(eq) /* yes, return NULL */ 158 159 tst r1, #BYTE2 /* does this byte match? */ 160 addeq r0, r2, #2 /* yes, point to it */ 161 RETc(eq) /* and return */ 162 tst r3, #BYTE2 /* is this byte NUL? */ 163 RETc(eq) /* yes, return NULL */ 164 165 tst r1, #BYTE3 /* does this byte match? */ 166 addeq r0, r2, #3 /* yes, point to it */ 167 /* 168 * Since no NULs and no matches this must be the only case left. 169 */ 170 RET /* return */ 171 #endif /* _ARM_ARCH_6 */ 172 END(strchr) 173
Indexes created Sun Sep 21 16:09:51 GMT 2025