1/* 2 * memchr - scan memory for a character 3 * 4 * Copyright (c) 2010-2021, Arm Limited. 5 * SPDX-License-Identifier: MIT 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 .arch armv7-a 27 28@ this lets us check a flag in a 00/ff byte easily in either endianness 29#ifdef __ARMEB__ 30#define CHARTSTMASK(c) 1<<(31-(c*8)) 31#else 32#define CHARTSTMASK(c) 1<<(c*8) 33#endif 34 .thumb 35 36@ --------------------------------------------------------------------------- 37 .thumb_func 38 .align 2 39 .p2align 4,,15 40 .global __memchr_arm 41 .type __memchr_arm,%function 42__memchr_arm: 43 @ r0 = start of memory to scan 44 @ r1 = character to look for 45 @ r2 = length 46 @ returns r0 = pointer to character or NULL if not found 47 and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char 48 49 cmp r2,#16 @ If it's short don't bother with anything clever 50 blt 20f 51 52 tst r0, #7 @ If it's already aligned skip the next bit 53 beq 10f 54 55 @ Work up to an aligned point 565: 57 ldrb r3, [r0],#1 58 subs r2, r2, #1 59 cmp r3, r1 60 beq 50f @ If it matches exit found 61 tst r0, #7 62 bne 5b @ If not aligned yet then do next byte 63 6410: 65 @ At this point, we are aligned, we know we have at least 8 bytes to work with 66 push {r4,r5,r6,r7} 67 orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes 68 orr r1, r1, r1, lsl #16 69 bic r4, r2, #7 @ Number of double words to work with 70 mvns r7, #0 @ all F's 71 movs r3, #0 72 7315: 74 ldmia r0!,{r5,r6} 75 subs r4, r4, #8 76 eor r5,r5, r1 @ Get it so that r5,r6 have 00's where the bytes match the target 77 eor r6,r6, r1 78 uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0 79 sel r5, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION 80 uadd8 r6, r6, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0 81 sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION 82 cbnz r6, 60f 83 bne 15b @ (Flags from the subs above) If not run out of bytes then go around again 84 85 pop {r4,r5,r6,r7} 86 and r1,r1,#0xff @ Get r1 back to a single character from the expansion above 87 and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done 88 8920: 90 cbz r2, 40f @ 0 length or hit the end already then not found 91 9221: @ Post aligned section, or just a short call 93 ldrb r3,[r0],#1 94 subs r2,r2,#1 95 eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub 96 cbz r3, 50f 97 bne 21b @ on r2 flags 98 9940: 100 movs r0,#0 @ not found 101 bx lr 102 10350: 104 subs r0,r0,#1 @ found 105 bx lr 106 10760: @ We're here because the fast path found a hit - now we have to track down exactly which word it was 108 @ r0 points to the start of the double word after the one that was tested 109 @ r5 has the 00/ff pattern for the first word, r6 has the chained value 110 cmp r5, #0 111 itte eq 112 moveq r5, r6 @ the end is in the 2nd word 113 subeq r0,r0,#3 @ Points to 2nd byte of 2nd word 114 subne r0,r0,#7 @ or 2nd byte of 1st word 115 116 @ r0 currently points to the 3rd byte of the word containing the hit 117 tst r5, # CHARTSTMASK(0) @ 1st character 118 bne 61f 119 adds r0,r0,#1 120 tst r5, # CHARTSTMASK(1) @ 2nd character 121 ittt eq 122 addeq r0,r0,#1 123 tsteq r5, # (3<<15) @ 2nd & 3rd character 124 @ If not the 3rd must be the last one 125 addeq r0,r0,#1 126 12761: 128 pop {r4,r5,r6,r7} 129 subs r0,r0,#1 130 bx lr 131 132 .size __memchr_arm, . - __memchr_arm 133