; Copyright (c) 2010-2011, Linaro Limited ; All rights reserved. ; ; Redistribution and use in source and binary forms, with or without ; modification, are permitted provided that the following conditions ; are met: ; ; * Redistributions of source code must retain the above copyright ; notice, this list of conditions and the following disclaimer. ; ; * Redistributions in binary form must reproduce the above copyright ; notice, this list of conditions and the following disclaimer in the ; documentation and/or other materials provided with the distribution. ; ; * Neither the name of Linaro Limited nor the names of its ; contributors may be used to endorse or promote products derived ; from this software without specific prior written permission. ; ; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ; "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT ; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR ; A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT ; HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, ; SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT ; LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, ; DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY ; THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE ; OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ; ; ; Written by Dave Gilbert ; ; This memchr routine is optimised on a Cortex-A9 and should work on ; all ARMv7 processors. It has a fast past 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. ; ; 2011-02-07 david.gilbert@linaro.org ; Extracted from local git a5b438d861 ; 2011-07-14 david.gilbert@linaro.org ; Import endianness fix from local git ea786f1b ; 2011-12-07 david.gilbert@linaro.org ; Removed unneeded cbz from align loop ; this lets us check a flag in a 00/ff byte easily in either endianness #define CHARTSTMASK(c) 1<<(c*8) EXPORT InternalMemScanMem8 AREA ScanMem, CODE, READONLY THUMB InternalMemScanMem8 ; r0 = start of memory to scan ; r1 = length ; r2 = character to look for ; returns r0 = pointer to character or NULL if not found uxtb r2, r2 ; Don't think we can trust the caller to actually pass a char cmp r1, #16 ; If it's short don't bother with anything clever blt L20 tst r0, #7 ; If it's already aligned skip the next bit beq L10 ; Work up to an aligned point L5 ldrb r3, [r0],#1 subs r1, r1, #1 cmp r3, r2 beq L50 ; If it matches exit found tst r0, #7 bne L5 ; If not aligned yet then do next byte L10 ; At this point, we are aligned, we know we have at least 8 bytes to work with push {r4-r7} orr r2, r2, r2, lsl #8 ; expand the match word across to all bytes orr r2, r2, r2, lsl #16 bic r4, r1, #7 ; Number of double words to work with mvns r7, #0 ; all F's movs r3, #0 L15 ldmia r0!, {r5,r6} subs r4, r4, #8 eor r5, r5, r2 ; Get it so that r5,r6 have 00's where the bytes match the target eor r6, r6, r2 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, L60 bne L15 ; (Flags from the subs above) If not run out of bytes then go around again pop {r4-r7} and r2, r2, #0xff ; Get r2 back to a single character from the expansion above and r1, r1, #7 ; Leave the count remaining as the number after the double words have been done L20 cbz r1, L40 ; 0 length or hit the end already then not found L21 ; Post aligned section, or just a short call ldrb r3, [r0], #1 subs r1, r1, #1 eor r3, r3, r2 ; r3 = 0 if match - doesn't break flags from sub cbz r3, L50 bne L21 ; on r1 flags L40 movs r0, #0 ; not found bx lr L50 subs r0, r0, #1 ; found bx lr L60 ; 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 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 3rd byte of the word containing the hit tst r5, #CHARTSTMASK(0) ; 1st character bne L61 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 L61 pop {r4-r7} subs r0, r0, #1 bx lr END