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; Copyright (c) 2010-2011, Linaro Limited
; All rights reserved.
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
;
; 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
; 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
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