1 /*
2 * Copyright (c) 2008 ARM Ltd
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. The name of the company may not be used to endorse or promote
14 * products derived from this software without specific prior written
15 * permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
22 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
23 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
24 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
25 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
26 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 #include "arm_asm.h"
30 #include <_ansi.h>
31 #include <string.h>
32 #include <limits.h>
33
34 #if defined (__OPTIMIZE_SIZE__) || defined (PREFER_SIZE_OVER_SPEED) || \
35 (defined (__thumb__) && !defined (__thumb2__))
36
37 # if !defined (PREFER_SIZE_OVER_SPEED) && !defined (__OPTIMIZE_SIZE__)
38 /* Thumb1 only variant.
39 If speed is preferred, the strlen() function in ../../string/strlen.c
40 will be used.
41
42 Leave this field blank. So the strlen() is not defined, and this will
43 automatically pull in the default C definition of strlen() from
44 ../../string/strlen.c. No need to include this file explicitely.
45 The lib_a-strlen.o will not be generated, so it won't replace the default
46 lib_a-strlen.o which is generated by ../../string/strlen.c. See the
47 commands in configure.in and Makefile.am for more details.
48
49 However, if we need to rewrite this function to be more efficient,
50 we can add the corresponding assembly code into this field and change
51 the commands in configure.in and Makefile.am to allow the corresponding
52 lib_a-strlen.o to be generated.
53 */
54 # else
55 size_t
strlen(const char * str)56 strlen (const char* str)
57 {
58 int scratch;
59 #if defined (__thumb__) && !defined (__thumb2__)
60 size_t len;
61 asm ("mov %0, #0\n"
62 "1:\n\t"
63 "ldrb %1, [%2, %0]\n\t"
64 "add %0, %0, #1\n\t"
65 "cmp %1, #0\n\t"
66 "bne 1b"
67 : "=&r" (len), "=&r" (scratch) : "r" (str) : "memory", "cc");
68 return len - 1;
69 #else
70 const char* end;
71 asm ("1:\n\t"
72 "ldrb %1, [%0], #1\n\t"
73 "cmp %1, #0\n\t"
74 "bne 1b"
75 : "=&r" (end), "=&r" (scratch) : "0" (str) : "memory", "cc");
76 return end - str - 1;
77 #endif
78 }
79 #endif
80 #else
81
82 #if !(defined(_ISA_ARM_7) || defined(__ARM_ARCH_6T2__))
83
84 size_t __attribute__((naked))
strlen(const char * str)85 strlen (const char* str)
86 {
87 (void)str; /* disable unused argument warning */
88 asm ("len .req r0\n\t"
89 "data .req r3\n\t"
90 "addr .req r1\n\t"
91
92 "optpld r0\n\t"
93 /* Word-align address */
94 "bic addr, r0, #3\n\t"
95 /* Get adjustment for start ... */
96 "ands len, r0, #3\n\t"
97 "neg len, len\n\t"
98 /* First word of data */
99 "ldr data, [addr], #4\n\t"
100 /* Ensure bytes preceeding start ... */
101 "add ip, len, #4\n\t"
102 "mov ip, ip, asl #3\n\t"
103 "mvn r2, #0\n\t"
104 /* ... are masked out */
105 #ifdef __thumb__
106 "itt ne\n\t"
107 # ifdef __ARMEB__
108 "lslne r2, ip\n\t"
109 # else
110 "lsrne r2, ip\n\t"
111 # endif
112 "orrne data, data, r2\n\t"
113 #else
114 "it ne\n\t"
115 # ifdef __ARMEB__
116 "orrne data, data, r2, lsl ip\n\t"
117 # else
118 "orrne data, data, r2, lsr ip\n\t"
119 # endif
120 #endif
121 /* Magic const 0x01010101 */
122 #ifdef _ISA_ARM_7
123 "movw ip, #0x101\n\t"
124 #else
125 "mov ip, #0x1\n\t"
126 "orr ip, ip, ip, lsl #8\n\t"
127 #endif
128 "orr ip, ip, ip, lsl #16\n"
129
130 /* This is the main loop. We subtract one from each byte in
131 the word: the sign bit changes iff the byte was zero or
132 0x80 -- we eliminate the latter case by anding the result
133 with the 1-s complement of the data. */
134 "1:\n\t"
135 /* test (data - 0x01010101) */
136 "sub r2, data, ip\n\t"
137 /* ... & ~data */
138 "bic r2, r2, data\n\t"
139 /* ... & 0x80808080 == 0? */
140 "ands r2, r2, ip, lsl #7\n\t"
141 #ifdef _ISA_ARM_7
142 /* yes, get more data... */
143 "itt eq\n\t"
144 "ldreq data, [addr], #4\n\t"
145 /* and 4 more bytes */
146 "addeq len, len, #4\n\t"
147 /* If we have PLD, then unroll the loop a bit. */
148 "optpld addr, #8\n\t"
149 /* test (data - 0x01010101) */
150 "ittt eq\n\t"
151 "subeq r2, data, ip\n\t"
152 /* ... & ~data */
153 "biceq r2, r2, data\n\t"
154 /* ... & 0x80808080 == 0? */
155 "andeqs r2, r2, ip, lsl #7\n\t"
156 #endif
157 "itt eq\n\t"
158 /* yes, get more data... */
159 "ldreq data, [addr], #4\n\t"
160 /* and 4 more bytes */
161 "addeq len, len, #4\n\t"
162 "beq 1b\n\t"
163 #ifdef __ARMEB__
164 "tst data, #0xff000000\n\t"
165 "itttt ne\n\t"
166 "addne len, len, #1\n\t"
167 "tstne data, #0xff0000\n\t"
168 "addne len, len, #1\n\t"
169 "tstne data, #0xff00\n\t"
170 "it ne\n\t"
171 "addne len, len, #1\n\t"
172 #else
173 # ifdef _ISA_ARM_5
174 /* R2 is the residual sign bits from the above test. All we
175 need to do now is establish the position of the first zero
176 byte... */
177 /* Little-endian is harder, we need the number of trailing
178 zeros / 8 */
179 # ifdef _ISA_ARM_7
180 "rbit r2, r2\n\t"
181 "clz r2, r2\n\t"
182 # else
183 "rsb r1, r2, #0\n\t"
184 "and r2, r2, r1\n\t"
185 "clz r2, r2\n\t"
186 "rsb r2, r2, #31\n\t"
187 # endif
188 "add len, len, r2, lsr #3\n\t"
189 # else /* No CLZ instruction */
190 "tst data, #0xff\n\t"
191 "itttt ne\n\t"
192 "addne len, len, #1\n\t"
193 "tstne data, #0xff00\n\t"
194 "addne len, len, #1\n\t"
195 "tstne data, #0xff0000\n\t"
196 "it ne\n\t"
197 "addne len, len, #1\n\t"
198 # endif
199 #endif
200 "RETURN");
201 }
202 #endif
203 #endif
204