1 /* memcmp - compare memory
3 Copyright (c) 2013, Linaro Limited
6 Redistribution and use in source and binary forms, with or without
7 modification, are permitted provided that the following conditions are met:
8 * Redistributions of source code must retain the above copyright
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10 * Redistributions in binary form must reproduce the above copyright
11 notice, this list of conditions and the following disclaimer in the
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13 * Neither the name of the Linaro nor the
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15 derived from this software without specific prior written permission.
17 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
18 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
19 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
20 A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
21 HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
22 SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
23 LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
27 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */
34 .macro def_fn f p2align=0
42 /* Parameters and result. */
48 /* Internal variables. */
63 def_fn memcmp p2align=6
70 add limit_wd, limit, #7
71 lsr limit_wd, limit_wd, #3
72 /* Start of performance-critical section -- one 64B cache line. */
77 subs limit_wd, limit_wd, #1
78 eor diff, data1, data2 /* Non-zero if differences found. */
79 csinv endloop, diff, xzr, ne /* Last Dword or differences. */
80 cbz endloop, .Lloop_aligned
81 /* End of performance-critical section -- one 64B cache line. */
83 /* Not reached the limit, must have found a diff. */
84 cbnz limit_wd, .Lnot_limit
86 /* Limit % 8 == 0 => all bytes significant. */
90 lsl limit, limit, #3 /* Bits -> bytes. */
97 bic data1, data1, mask
98 bic data2, data2, mask
103 #ifndef __AARCH64EB__
108 /* The MS-non-zero bit of DIFF marks either the first bit
109 that is different, or the end of the significant data.
110 Shifting left now will bring the critical information into the
113 lsl data1, data1, pos
114 lsl data2, data2, pos
115 /* But we need to zero-extend (char is unsigned) the value and then
116 perform a signed 32-bit subtraction. */
117 lsr data1, data1, #56
118 sub result, data1, data2, lsr #56
122 /* Sources are mutually aligned, but are not currently at an
123 alignment boundary. Round down the addresses and then mask off
124 the bytes that precede the start point. */
127 add limit, limit, tmp1 /* Adjust the limit for the extra. */
128 lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
129 ldr data1, [src1], #8
130 neg tmp1, tmp1 /* Bits to alignment -64. */
131 ldr data2, [src2], #8
134 /* Big-endian. Early bytes are at MSB. */
135 lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
137 /* Little-endian. Early bytes are at LSB. */
138 lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
140 add limit_wd, limit, #7
141 orr data1, data1, tmp2
142 orr data2, data2, tmp2
143 lsr limit_wd, limit_wd, #3
154 /* Perhaps we can do better than this. */
155 ldrb data1w, [src1], #1
156 ldrb data2w, [src2], #1
157 subs limit, limit, #1
158 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
160 sub result, data1, data2
162 .size memcmp, . - memcmp