1; Copyright (c) 2010-2011, Linaro Limited
2; All rights reserved.
3;
4; Redistribution and use in source and binary forms, with or without
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7;
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10;
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14;
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19; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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22; A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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30;
31
32;
33; Written by Dave Gilbert <david.gilbert@linaro.org>
34;
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.
39;
40
41
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
48
49; this lets us check a flag in a 00/ff byte easily in either endianness
50#define CHARTSTMASK(c) 1<<(c*8)
51
52    EXPORT  InternalMemScanMem8
53    AREA    ScanMem, CODE, READONLY
54    THUMB
55
56InternalMemScanMem8
57    ; r0 = start of memory to scan
58    ; r1 = length
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
62
63    cmp     r1, #16       ; If it's short don't bother with anything clever
64    blt     L20
65
66    tst     r0, #7        ; If it's already aligned skip the next bit
67    beq     L10
68
69    ; Work up to an aligned point
70L5
71    ldrb    r3, [r0],#1
72    subs    r1, r1, #1
73    cmp     r3, r2
74    beq     L50           ; If it matches exit found
75    tst     r0, #7
76    bne     L5            ; If not aligned yet then do next byte
77
78L10
79    ; At this point, we are aligned, we know we have at least 8 bytes to work with
80    push    {r4-r7}
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
84    mvns    r7, #0        ; all F's
85    movs    r3, #0
86
87L15
88    ldmia   r0!, {r5,r6}
89    subs    r4, r4, #8
90    eor     r5, r5, r2    ; Get it so that r5,r6 have 00's where the bytes match the target
91    eor     r6, r6, r2
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
96    cbnz    r6, L60
97    bne     L15           ; (Flags from the subs above) If not run out of bytes then go around again
98
99    pop     {r4-r7}
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
102
103L20
104    cbz     r1, L40       ; 0 length or hit the end already then not found
105
106L21 ; Post aligned section, or just a short call
107    ldrb    r3, [r0], #1
108    subs    r1, r1, #1
109    eor     r3, r3, r2    ; r3 = 0 if match - doesn't break flags from sub
110    cbz     r3, L50
111    bne     L21           ; on r1 flags
112
113L40
114    movs    r0, #0        ; not found
115    bx      lr
116
117L50
118    subs    r0, r0, #1    ; found
119    bx      lr
120
121L60 ; 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
124    cmp     r5, #0
125    itte    eq
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
129
130    ; r0 currently points to the 3rd byte of the word containing the hit
131    tst     r5, #CHARTSTMASK(0)     ; 1st character
132    bne     L61
133    adds    r0, r0, #1
134    tst     r5, #CHARTSTMASK(1)     ; 2nd character
135    ittt    eq
136    addeq   r0, r0 ,#1
137    tsteq   r5, #(3 << 15)          ; 2nd & 3rd character
138    ; If not the 3rd must be the last one
139    addeq   r0, r0, #1
140
141L61
142    pop     {r4-r7}
143    subs    r0, r0, #1
144    bx      lr
145
146    END
147
148