1// Copyright (c) 2010-2011, Linaro Limited
2// All rights reserved.
3//
4// Redistribution and use in source and binary forms, with or without
5// modification, are permitted provided that the following conditions
6// are met:
7//
8//    * Redistributions of source code must retain the above copyright
9//    notice, this list of conditions and the following disclaimer.
10//
11//    * Redistributions in binary form must reproduce the above copyright
12//    notice, this list of conditions and the following disclaimer in the
13//    documentation and/or other materials provided with the distribution.
14//
15//    * Neither the name of Linaro Limited nor the names of its
16//    contributors may be used to endorse or promote products derived
17//    from this software without specific prior written permission.
18//
19// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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25// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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29// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30//
31
32//
33// Written by Dave Gilbert <[email protected]>
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 [email protected]
43//    Extracted from local git a5b438d861
44// 2011-07-14 [email protected]
45//    Import endianness fix from local git ea786f1b
46// 2011-12-07 [email protected]
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    .text
53    .thumb
54    .syntax unified
55
56    .type ASM_PFX(InternalMemScanMem8), %function
57ASM_GLOBAL ASM_PFX(InternalMemScanMem8)
58ASM_PFX(InternalMemScanMem8):
59    // r0 = start of memory to scan
60    // r1 = length
61    // r2 = character to look for
62    // returns r0 = pointer to character or NULL if not found
63    uxtb    r2, r2        // Don't think we can trust the caller to actually pass a char
64
65    cmp     r1, #16       // If it's short don't bother with anything clever
66    blt     20f
67
68    tst     r0, #7        // If it's already aligned skip the next bit
69    beq     10f
70
71    // Work up to an aligned point
725:
73    ldrb    r3, [r0],#1
74    subs    r1, r1, #1
75    cmp     r3, r2
76    beq     50f           // If it matches exit found
77    tst     r0, #7
78    bne     5b            // If not aligned yet then do next byte
79
8010:
81    // At this point, we are aligned, we know we have at least 8 bytes to work with
82    push    {r4-r7}
83    orr     r2, r2, r2, lsl #8  // expand the match word across to all bytes
84    orr     r2, r2, r2, lsl #16
85    bic     r4, r1, #7    // Number of double words to work with
86    mvns    r7, #0        // all F's
87    movs    r3, #0
88
8915:
90    ldmia   r0!, {r5,r6}
91    subs    r4, r4, #8
92    eor     r5, r5, r2    // Get it so that r5,r6 have 00's where the bytes match the target
93    eor     r6, r6, r2
94    uadd8   r5, r5, r7    // Parallel add 0xff - sets the GE bits for anything that wasn't 0
95    sel     r5, r3, r7    // bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
96    uadd8   r6, r6, r7    // Parallel add 0xff - sets the GE bits for anything that wasn't 0
97    sel     r6, r5, r7    // chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
98    cbnz    r6, 60f
99    bne     15b           // (Flags from the subs above) If not run out of bytes then go around again
100
101    pop     {r4-r7}
102    and     r2, r2, #0xff // Get r2 back to a single character from the expansion above
103    and     r1, r1, #7    // Leave the count remaining as the number after the double words have been done
104
10520:
106    cbz     r1, 40f       // 0 length or hit the end already then not found
107
10821: // Post aligned section, or just a short call
109    ldrb    r3, [r0], #1
110    subs    r1, r1, #1
111    eor     r3, r3, r2    // r3 = 0 if match - doesn't break flags from sub
112    cbz     r3, 50f
113    bne     21b           // on r1 flags
114
11540:
116    movs    r0, #0        // not found
117    bx      lr
118
11950:
120    subs    r0, r0, #1    // found
121    bx      lr
122
12360: // We're here because the fast path found a hit - now we have to track down exactly which word it was
124    // r0 points to the start of the double word after the one that was tested
125    // r5 has the 00/ff pattern for the first word, r6 has the chained value
126    subs    r0, r0, #3
127    cmp     r5, #0
128    it      eq
129    moveq.n r5, r6        // the end is in the 2nd word
130    it      ne
131    subne.n r0, r0, #4    // or 2nd byte of 1st word
132
133    // r0 currently points to the 3rd byte of the word containing the hit
134    tst     r5, #CHARTSTMASK(0)     // 1st character
135    bne     61f
136    adds    r0, r0, #1
137    tst     r5, #CHARTSTMASK(1)     // 2nd character
138    bne     61f
139    adds    r0, r0 ,#1
140    tst     r5, #(3 << 15)          // 2nd & 3rd character
141    // If not the 3rd must be the last one
142    it      eq
143    addeq.n r0, r0, #1
144
14561:
146    pop     {r4-r7}
147    subs    r0, r0, #1
148    bx      lr
149