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33 ; Written by Dave Gilbert <david.gilbert@linaro.org>
35 ; This memchr routine is optimised on a Cortex-A9 and should work on
36 ; all ARMv7 processors. It has a fast past for short sizes, and has
37 ; an optimised path for large data sets; the worst case is finding the
38 ; match early in a large data set.
42 ; 2011-02-07 david.gilbert@linaro.org
43 ; Extracted from local git a5b438d861
44 ; 2011-07-14 david.gilbert@linaro.org
45 ; Import endianness fix from local git ea786f1b
46 ; 2011-12-07 david.gilbert@linaro.org
47 ; Removed unneeded cbz from align loop
49 ; this lets us check a flag in a 00/ff byte easily in either endianness
50 #define CHARTSTMASK(c) 1<<(c*8)
52 EXPORT InternalMemScanMem8
53 AREA ScanMem, CODE, READONLY
57 ; r0 = start of memory to scan
59 ; r2 = character to look for
60 ; returns r0 = pointer to character or NULL if not found
61 uxtb r2, r2 ; Don't think we can trust the caller to actually pass a char
63 cmp r1, #16 ; If it's short don't bother with anything clever
66 tst r0, #7 ; If it's already aligned skip the next bit
69 ; Work up to an aligned point
74 beq L50 ; If it matches exit found
76 bne L5 ; If not aligned yet then do next byte
79 ; At this point, we are aligned, we know we have at least 8 bytes to work with
81 orr r2, r2, r2, lsl #8 ; expand the match word across to all bytes
82 orr r2, r2, r2, lsl #16
83 bic r4, r1, #7 ; Number of double words to work with
90 eor r5, r5, r2 ; Get it so that r5,r6 have 00's where the bytes match the target
92 uadd8 r5, r5, r7 ; Parallel add 0xff - sets the GE bits for anything that wasn't 0
93 sel r5, r3, r7 ; bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
94 uadd8 r6, r6, r7 ; Parallel add 0xff - sets the GE bits for anything that wasn't 0
95 sel r6, r5, r7 ; chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
97 bne L15 ; (Flags from the subs above) If not run out of bytes then go around again
100 and r2, r2, #0xff ; Get r2 back to a single character from the expansion above
101 and r1, r1, #7 ; Leave the count remaining as the number after the double words have been done
104 cbz r1, L40 ; 0 length or hit the end already then not found
106 L21 ; Post aligned section, or just a short call
109 eor r3, r3, r2 ; r3 = 0 if match - doesn't break flags from sub
111 bne L21 ; on r1 flags
114 movs r0, #0 ; not found
118 subs r0, r0, #1 ; found
121 L60 ; We're here because the fast path found a hit - now we have to track down exactly which word it was
122 ; r0 points to the start of the double word after the one that was tested
123 ; r5 has the 00/ff pattern for the first word, r6 has the chained value
126 moveq r5, r6 ; the end is in the 2nd word
127 subeq r0, r0, #3 ; Points to 2nd byte of 2nd word
128 subne r0, r0, #7 ; or 2nd byte of 1st word
130 ; r0 currently points to the 3rd byte of the word containing the hit
131 tst r5, #CHARTSTMASK(0) ; 1st character
134 tst r5, #CHARTSTMASK(1) ; 2nd character
137 tsteq r5, #(3 << 15) ; 2nd & 3rd character
138 ; If not the 3rd must be the last one