1/* 2 * memchr - scan memory for a character 3 * 4 * Copyright (c) 2010-2022, Arm Limited. 5 * SPDX-License-Identifier: MIT OR Apache-2.0 WITH LLVM-exception 6 */ 7 8/* 9 Written by Dave Gilbert <david.gilbert@linaro.org> 10 11 This __memchr_arm routine is optimised on a Cortex-A9 and should work on 12 all ARMv7 processors. It has a fast past for short sizes, and has 13 an optimised path for large data sets; the worst case is finding the 14 match early in a large data set. 15 16 */ 17 18@ 2011-02-07 david.gilbert@linaro.org 19@ Extracted from local git a5b438d861 20@ 2011-07-14 david.gilbert@linaro.org 21@ Import endianness fix from local git ea786f1b 22@ 2011-12-07 david.gilbert@linaro.org 23@ Removed unneeded cbz from align loop 24 25 .syntax unified 26#if __ARM_ARCH >= 8 && __ARM_ARCH_PROFILE == 'M' 27 /* keep config inherited from -march= */ 28#else 29 .arch armv7-a 30#endif 31 32@ this lets us check a flag in a 00/ff byte easily in either endianness 33#ifdef __ARMEB__ 34#define CHARTSTMASK(c) 1<<(31-(c*8)) 35#else 36#define CHARTSTMASK(c) 1<<(c*8) 37#endif 38 .thumb 39#include "asmdefs.h" 40 41 42@ --------------------------------------------------------------------------- 43 .thumb_func 44 .align 2 45 .p2align 4,,15 46 .global __memchr_arm 47 .type __memchr_arm,%function 48 .fnstart 49 .cfi_startproc 50__memchr_arm: 51 @ r0 = start of memory to scan 52 @ r1 = character to look for 53 @ r2 = length 54 @ returns r0 = pointer to character or NULL if not found 55 prologue 56 and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char 57 58 cmp r2,#16 @ If it's short don't bother with anything clever 59 blt 20f 60 61 tst r0, #7 @ If it's already aligned skip the next bit 62 beq 10f 63 64 @ Work up to an aligned point 655: 66 ldrb r3, [r0],#1 67 subs r2, r2, #1 68 cmp r3, r1 69 beq 50f @ If it matches exit found 70 tst r0, #7 71 bne 5b @ If not aligned yet then do next byte 72 7310: 74 @ At this point, we are aligned, we know we have at least 8 bytes to work with 75 push {r4,r5,r6,r7} 76 .cfi_adjust_cfa_offset 16 77 .cfi_rel_offset 4, 0 78 .cfi_rel_offset 5, 4 79 .cfi_rel_offset 6, 8 80 .cfi_rel_offset 7, 12 81 orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes 82 orr r1, r1, r1, lsl #16 83 bic r4, r2, #7 @ Number of double words to work with 84 mvns r7, #0 @ all F's 85 movs r3, #0 86 8715: 88 ldmia r0!,{r5,r6} 89 subs r4, r4, #8 90 eor r5,r5, r1 @ Get it so that r5,r6 have 00's where the bytes match the target 91 eor r6,r6, r1 92 uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0 93 sel r5, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION 94 uadd8 r6, r6, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0 95 sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION 96 cbnz r6, 60f 97 bne 15b @ (Flags from the subs above) If not run out of bytes then go around again 98 99 pop {r4,r5,r6,r7} 100 .cfi_restore 7 101 .cfi_restore 6 102 .cfi_restore 5 103 .cfi_restore 4 104 .cfi_adjust_cfa_offset -16 105 and r1,r1,#0xff @ Get r1 back to a single character from the expansion above 106 and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done 107 10820: 109 cbz r2, 40f @ 0 length or hit the end already then not found 110 11121: @ Post aligned section, or just a short call 112 ldrb r3,[r0],#1 113 subs r2,r2,#1 114 eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub 115 cbz r3, 50f 116 bne 21b @ on r2 flags 117 11840: 119 .cfi_remember_state 120 movs r0,#0 @ not found 121 epilogue 122 12350: 124 .cfi_restore_state 125 .cfi_remember_state 126 subs r0,r0,#1 @ found 127 epilogue 128 12960: @ We're here because the fast path found a hit - now we have to track down exactly which word it was 130 @ r0 points to the start of the double word after the one that was tested 131 @ r5 has the 00/ff pattern for the first word, r6 has the chained value 132 .cfi_restore_state @ Standard post-prologue state 133 .cfi_adjust_cfa_offset 16 134 .cfi_rel_offset 4, 0 135 .cfi_rel_offset 5, 4 136 .cfi_rel_offset 6, 8 137 .cfi_rel_offset 7, 12 138 cmp r5, #0 139 itte eq 140 moveq r5, r6 @ the end is in the 2nd word 141 subeq r0,r0,#3 @ Points to 2nd byte of 2nd word 142 subne r0,r0,#7 @ or 2nd byte of 1st word 143 144 @ r0 currently points to the 3rd byte of the word containing the hit 145 tst r5, # CHARTSTMASK(0) @ 1st character 146 bne 61f 147 adds r0,r0,#1 148 tst r5, # CHARTSTMASK(1) @ 2nd character 149 ittt eq 150 addeq r0,r0,#1 151 tsteq r5, # (3<<15) @ 2nd & 3rd character 152 @ If not the 3rd must be the last one 153 addeq r0,r0,#1 154 15561: 156 pop {r4,r5,r6,r7} 157 .cfi_restore 7 158 .cfi_restore 6 159 .cfi_restore 5 160 .cfi_restore 4 161 .cfi_adjust_cfa_offset -16 162 subs r0,r0,#1 163 epilogue 164 .cfi_endproc 165 .cantunwind 166 .fnend 167 168 .size __memchr_arm, . - __memchr_arm 169