/* Copyright (C) 2011 Free Software Foundation, Inc. This file is part of the GNU C Library. Code contributed by Dave Gilbert The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library. If not, see . */ #include @ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7 @ and ARMv6T2 processors. It has a fast path for short sizes, and has an @ optimised path for large data sets; the worst case is finding the match early @ in a large data set. @ Note: The use of cbz/cbnz means it's Thumb only @ 2011-07-15 david.gilbert@linaro.org @ Copy from Cortex strings release 21 and change license @ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S @ Change function declarations/entry/exit @ 2011-12-01 david.gilbert@linaro.org @ Add some fixes from comments received (including use of ldrd instead ldm) @ 2011-12-07 david.gilbert@linaro.org @ Removed cbz from align loop - can't be taken @ this lets us check a flag in a 00/ff byte easily in either endianness #ifdef __ARMEB__ #define CHARTSTMASK(c) 1<<(31-(c*8)) #else #define CHARTSTMASK(c) 1<<(c*8) #endif .syntax unified .text .thumb @ --------------------------------------------------------------------------- .thumb_func .global memchr .type memchr,%function ENTRY(memchr) @ r0 = start of memory to scan @ r1 = character to look for @ r2 = length @ returns r0 = pointer to character or NULL if not found and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char cmp r2,#16 @ If it's short don't bother with anything clever blt 20f tst r0, #7 @ If it's already aligned skip the next bit beq 10f @ Work up to an aligned point 5: ldrb r3, [r0],#1 subs r2, r2, #1 cmp r3, r1 beq 50f @ If it matches exit found tst r0, #7 bne 5b @ If not aligned yet then do next byte 10: @ At this point, we are aligned, we know we have at least 8 bytes to work with push {r4,r5,r6,r7} cfi_adjust_cfa_offset (16) cfi_rel_offset (r4, 0) cfi_rel_offset (r5, 4) cfi_rel_offset (r6, 8) cfi_rel_offset (r7, 12) cfi_remember_state orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes orr r1, r1, r1, lsl #16 bic r4, r2, #7 @ Number of double words to work with * 8 mvns r7, #0 @ all F's movs r3, #0 15: ldrd r5,r6, [r0],#8 subs r4, r4, #8 eor r5,r5, r1 @ Get it so that r5,r6 have 00's where the bytes match the target eor r6,r6, r1 uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0 sel r5, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION uadd8 r6, r6, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0 sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION cbnz r6, 60f bne 15b @ (Flags from the subs above) If not run out of bytes then go around again pop {r4,r5,r6,r7} cfi_adjust_cfa_offset (-16) cfi_restore (r4) cfi_restore (r5) cfi_restore (r6) cfi_restore (r7) and r1,r1,#0xff @ Get r1 back to a single character from the expansion above and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done 20: cbz r2, 40f @ 0 length or hit the end already then not found 21: @ Post aligned section, or just a short call ldrb r3,[r0],#1 subs r2,r2,#1 eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub cbz r3, 50f bne 21b @ on r2 flags 40: movs r0,#0 @ not found DO_RET(lr) 50: subs r0,r0,#1 @ found DO_RET(lr) 60: @ We're here because the fast path found a hit - now we have to track down exactly which word it was @ r0 points to the start of the double word after the one that was tested @ r5 has the 00/ff pattern for the first word, r6 has the chained value cfi_restore_state cmp r5, #0 itte eq moveq r5, r6 @ the end is in the 2nd word subeq r0,r0,#3 @ Points to 2nd byte of 2nd word subne r0,r0,#7 @ or 2nd byte of 1st word @ r0 currently points to the 2nd byte of the word containing the hit tst r5, # CHARTSTMASK(0) @ 1st character bne 61f adds r0,r0,#1 tst r5, # CHARTSTMASK(1) @ 2nd character ittt eq addeq r0,r0,#1 tsteq r5, # (3<<15) @ 2nd & 3rd character @ If not the 3rd must be the last one addeq r0,r0,#1 61: pop {r4,r5,r6,r7} cfi_adjust_cfa_offset (-16) cfi_restore (r4) cfi_restore (r5) cfi_restore (r6) cfi_restore (r7) subs r0,r0,#1 DO_RET(lr) END(memchr) libc_hidden_builtin_def (memchr)