/
memchr.S
124 lines (101 loc) · 5.05 KB
/
memchr.S
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.syntax unified
.arch armv7-a
@ 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 <david.gilbert@linaro.org>
@ 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
.text
.thumb
@ ---------------------------------------------------------------------------
.thumb_func
.align 2
.p2align 4,,15
.global memchr
.type memchr,%function
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
cbz r2, 40f @ If we run off the end, exit not found
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}
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
mvns r7, #0 @ all F's
movs r3, #0
15:
ldmia r0!,{r5,r6}
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}
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
bx lr
50:
subs r0,r0,#1 @ found
bx 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
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, # (1<<0) @ 1st character
bne 61f
adds r0,r0,#1
tst r5, # (1<<8) @ 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}
subs r0,r0,#1
bx lr