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1/* Copyright (C) 2012-2019 Free Software Foundation, Inc.
2
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library. If not, see
17 <http://www.gnu.org/licenses/>. */
18
19/* Assumptions:
20 *
21 * ARMv8-a, AArch64
22 */
23
24#include <sysdep.h>
25
26#define REP8_01 0x0101010101010101
27#define REP8_7f 0x7f7f7f7f7f7f7f7f
28#define REP8_80 0x8080808080808080
29
30/* Parameters and result. */
31#define src1 x0
32#define src2 x1
33#define result x0
34
35/* Internal variables. */
36#define data1 x2
37#define data1w w2
38#define data2 x3
39#define data2w w3
40#define has_nul x4
41#define diff x5
42#define syndrome x6
43#define tmp1 x7
44#define tmp2 x8
45#define tmp3 x9
46#define zeroones x10
47#define pos x11
48
49 /* Start of performance-critical section -- one 64B cache line. */
50ENTRY_ALIGN(strcmp, 6)
51
52 DELOUSE (0)
53 DELOUSE (1)
54 eor tmp1, src1, src2
55 mov zeroones, #REP8_01
56 tst tmp1, #7
57 b.ne L(misaligned8)
58 ands tmp1, src1, #7
59 b.ne L(mutual_align)
60 /* NUL detection works on the principle that (X - 1) & (~X) & 0x80
61 (=> (X - 1) & ~(X | 0x7f)) is non-zero iff a byte is zero, and
62 can be done in parallel across the entire word. */
63L(loop_aligned):
64 ldr data1, [src1], #8
65 ldr data2, [src2], #8
66L(start_realigned):
67 sub tmp1, data1, zeroones
68 orr tmp2, data1, #REP8_7f
69 eor diff, data1, data2 /* Non-zero if differences found. */
70 bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
71 orr syndrome, diff, has_nul
72 cbz syndrome, L(loop_aligned)
73 /* End of performance-critical section -- one 64B cache line. */
74
75L(end):
76#ifndef __AARCH64EB__
77 rev syndrome, syndrome
78 rev data1, data1
79 /* The MS-non-zero bit of the syndrome marks either the first bit
80 that is different, or the top bit of the first zero byte.
81 Shifting left now will bring the critical information into the
82 top bits. */
83 clz pos, syndrome
84 rev data2, data2
85 lsl data1, data1, pos
86 lsl data2, data2, pos
87 /* But we need to zero-extend (char is unsigned) the value and then
88 perform a signed 32-bit subtraction. */
89 lsr data1, data1, #56
90 sub result, data1, data2, lsr #56
91 RET
92#else
93 /* For big-endian we cannot use the trick with the syndrome value
94 as carry-propagation can corrupt the upper bits if the trailing
95 bytes in the string contain 0x01. */
96 /* However, if there is no NUL byte in the dword, we can generate
97 the result directly. We can't just subtract the bytes as the
98 MSB might be significant. */
99 cbnz has_nul, 1f
100 cmp data1, data2
101 cset result, ne
102 cneg result, result, lo
103 RET
1041:
105 /* Re-compute the NUL-byte detection, using a byte-reversed value. */
106 rev tmp3, data1
107 sub tmp1, tmp3, zeroones
108 orr tmp2, tmp3, #REP8_7f
109 bic has_nul, tmp1, tmp2
110 rev has_nul, has_nul
111 orr syndrome, diff, has_nul
112 clz pos, syndrome
113 /* The MS-non-zero bit of the syndrome marks either the first bit
114 that is different, or the top bit of the first zero byte.
115 Shifting left now will bring the critical information into the
116 top bits. */
117 lsl data1, data1, pos
118 lsl data2, data2, pos
119 /* But we need to zero-extend (char is unsigned) the value and then
120 perform a signed 32-bit subtraction. */
121 lsr data1, data1, #56
122 sub result, data1, data2, lsr #56
123 RET
124#endif
125
126L(mutual_align):
127 /* Sources are mutually aligned, but are not currently at an
128 alignment boundary. Round down the addresses and then mask off
129 the bytes that preceed the start point. */
130 bic src1, src1, #7
131 bic src2, src2, #7
132 lsl tmp1, tmp1, #3 /* Bytes beyond alignment -> bits. */
133 ldr data1, [src1], #8
134 neg tmp1, tmp1 /* Bits to alignment -64. */
135 ldr data2, [src2], #8
136 mov tmp2, #~0
137#ifdef __AARCH64EB__
138 /* Big-endian. Early bytes are at MSB. */
139 lsl tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
140#else
141 /* Little-endian. Early bytes are at LSB. */
142 lsr tmp2, tmp2, tmp1 /* Shift (tmp1 & 63). */
143#endif
144 orr data1, data1, tmp2
145 orr data2, data2, tmp2
146 b L(start_realigned)
147
148L(misaligned8):
149 /* Align SRC1 to 8 bytes and then compare 8 bytes at a time, always
150 checking to make sure that we don't access beyond page boundary in
151 SRC2. */
152 tst src1, #7
153 b.eq L(loop_misaligned)
154L(do_misaligned):
155 ldrb data1w, [src1], #1
156 ldrb data2w, [src2], #1
157 cmp data1w, #1
158 ccmp data1w, data2w, #0, cs /* NZCV = 0b0000. */
159 b.ne L(done)
160 tst src1, #7
161 b.ne L(do_misaligned)
162
163L(loop_misaligned):
164 /* Test if we are within the last dword of the end of a 4K page. If
165 yes then jump back to the misaligned loop to copy a byte at a time. */
166 and tmp1, src2, #0xff8
167 eor tmp1, tmp1, #0xff8
168 cbz tmp1, L(do_misaligned)
169 ldr data1, [src1], #8
170 ldr data2, [src2], #8
171
172 sub tmp1, data1, zeroones
173 orr tmp2, data1, #REP8_7f
174 eor diff, data1, data2 /* Non-zero if differences found. */
175 bic has_nul, tmp1, tmp2 /* Non-zero if NUL terminator. */
176 orr syndrome, diff, has_nul
177 cbz syndrome, L(loop_misaligned)
178 b L(end)
179
180L(done):
181 sub result, data1, data2
182 RET
183END(strcmp)
184libc_hidden_builtin_def (strcmp)
185

Warning: That file was not part of the compilation database. It may have many parsing errors.