1 | /* strchr (str, ch) -- Return pointer to first occurrence of CH in STR. |
2 | For Motorola 68000. |
3 | Copyright (C) 1999-2022 Free Software Foundation, Inc. |
4 | This file is part of the GNU C Library. |
5 | |
6 | The GNU C Library is free software; you can redistribute it and/or |
7 | modify it under the terms of the GNU Lesser General Public |
8 | License as published by the Free Software Foundation; either |
9 | version 2.1 of the License, or (at your option) any later version. |
10 | |
11 | The GNU C Library is distributed in the hope that it will be useful, |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
14 | Lesser General Public License for more details. |
15 | |
16 | You should have received a copy of the GNU Lesser General Public |
17 | License along with the GNU C Library. If not, see |
18 | <https://www.gnu.org/licenses/>. */ |
19 | |
20 | #include <sysdep.h> |
21 | #include "asm-syntax.h" |
22 | |
23 | TEXT |
24 | ENTRY(strchr) |
25 | /* Save the callee-saved registers we use. */ |
26 | movel R(d2),MEM_PREDEC(sp) |
27 | cfi_adjust_cfa_offset (4) |
28 | movel R(d3),MEM_PREDEC(sp) |
29 | cfi_adjust_cfa_offset (4) |
30 | cfi_rel_offset (R(d2),4) |
31 | cfi_rel_offset (R(d3),0) |
32 | |
33 | /* Get string pointer and character. */ |
34 | movel MEM_DISP(sp,12),R(a0) |
35 | moveb MEM_DISP(sp,19),R(d0) |
36 | |
37 | /* Distribute the character to all bytes of a longword. */ |
38 | movel R(d0),R(d1) |
39 | lsll #8,R(d1) |
40 | moveb R(d0),R(d1) |
41 | movel R(d1),R(d0) |
42 | swap R(d0) |
43 | movew R(d1),R(d0) |
44 | |
45 | /* First search for the character one byte at a time until the |
46 | pointer is aligned to a longword boundary. */ |
47 | movel R(a0),R(d1) |
48 | #ifdef __mcoldfire__ |
49 | andl #3,R(d1) |
50 | #else |
51 | andw #3,R(d1) |
52 | #endif |
53 | beq L(L1) |
54 | moveb MEM(a0),R(d2) |
55 | cmpb R(d0),R(d2) |
56 | beq L(L9) |
57 | tstb R(d2) |
58 | beq L(L3) |
59 | addql #1,R(a0) |
60 | |
61 | #ifdef __mcoldfire__ |
62 | subql #3,R(d1) |
63 | #else |
64 | subqw #3,R(d1) |
65 | #endif |
66 | beq L(L1) |
67 | moveb MEM(a0),R(d2) |
68 | cmpb R(d0),R(d2) |
69 | beq L(L9) |
70 | tstb R(d2) |
71 | beq L(L3) |
72 | addql #1,R(a0) |
73 | |
74 | #ifdef __mcoldfire__ |
75 | addql #1,R(d1) |
76 | #else |
77 | addqw #1,R(d1) |
78 | #endif |
79 | beq L(L1) |
80 | moveb MEM(a0),R(d2) |
81 | cmpb R(d0),R(d2) |
82 | beq L(L9) |
83 | tstb R(d2) |
84 | beq L(L3) |
85 | addql #1,R(a0) |
86 | |
87 | L(L1:) |
88 | /* Load the magic bits. Unlike the generic implementation we can |
89 | use the carry bit as the fourth hole. */ |
90 | movel #0xfefefeff,R(d3) |
91 | |
92 | /* We exit the loop if adding MAGIC_BITS to LONGWORD fails to |
93 | change any of the hole bits of LONGWORD. |
94 | |
95 | 1) Is this safe? Will it catch all the zero bytes? |
96 | Suppose there is a byte with all zeros. Any carry bits |
97 | propagating from its left will fall into the hole at its |
98 | least significant bit and stop. Since there will be no |
99 | carry from its most significant bit, the LSB of the |
100 | byte to the left will be unchanged, and the zero will be |
101 | detected. |
102 | |
103 | 2) Is this worthwhile? Will it ignore everything except |
104 | zero bytes? Suppose every byte of LONGWORD has a bit set |
105 | somewhere. There will be a carry into bit 8. If bit 8 |
106 | is set, this will carry into bit 16. If bit 8 is clear, |
107 | one of bits 9-15 must be set, so there will be a carry |
108 | into bit 16. Similarly, there will be a carry into bit |
109 | 24. If one of bits 24-31 is set, there will be a carry |
110 | into bit 32 (=carry flag), so all of the hole bits will |
111 | be changed. |
112 | |
113 | 3) But wait! Aren't we looking for C, not zero? |
114 | Good point. So what we do is XOR LONGWORD with a longword, |
115 | each of whose bytes is C. This turns each byte that is C |
116 | into a zero. */ |
117 | |
118 | L(L2:) |
119 | /* Get the longword in question. */ |
120 | movel MEM_POSTINC(a0),R(d1) |
121 | /* XOR with the byte we search for. */ |
122 | eorl R(d0),R(d1) |
123 | |
124 | /* Add the magic value. We get carry bits reported for each byte |
125 | which is not C. */ |
126 | movel R(d3),R(d2) |
127 | addl R(d1),R(d2) |
128 | |
129 | /* Check the fourth carry bit before it is clobbered by the next |
130 | XOR. If it is not set we have a hit. */ |
131 | bcc L(L8) |
132 | |
133 | /* We are only interested in carry bits that change due to the |
134 | previous add, so remove original bits. */ |
135 | eorl R(d1),R(d2) |
136 | |
137 | /* Now test for the other three overflow bits. |
138 | Set all non-carry bits. */ |
139 | orl R(d3),R(d2) |
140 | /* Add 1 to get zero if all carry bits were set. */ |
141 | addql #1,R(d2) |
142 | |
143 | /* If we don't get zero then at least one byte of the word equals |
144 | C. */ |
145 | bne L(L8) |
146 | |
147 | /* Next look for a NUL byte. |
148 | Restore original longword without reload. */ |
149 | eorl R(d0),R(d1) |
150 | /* Add the magic value. We get carry bits reported for each byte |
151 | which is not NUL. */ |
152 | movel R(d3),R(d2) |
153 | addl R(d1),R(d2) |
154 | |
155 | /* Check the fourth carry bit before it is clobbered by the next |
156 | XOR. If it is not set we have a hit, and return NULL. */ |
157 | bcc L(L3) |
158 | |
159 | /* We are only interested in carry bits that change due to the |
160 | previous add, so remove original bits. */ |
161 | eorl R(d1),R(d2) |
162 | |
163 | /* Now test for the other three overflow bits. |
164 | Set all non-carry bits. */ |
165 | orl R(d3),R(d2) |
166 | /* Add 1 to get zero if all carry bits were set. */ |
167 | addql #1,R(d2) |
168 | |
169 | /* If we don't get zero then at least one byte of the word was NUL |
170 | and we return NULL. Otherwise continue with the next longword. */ |
171 | bne L(L3) |
172 | |
173 | /* Get the longword in question. */ |
174 | movel MEM_POSTINC(a0),R(d1) |
175 | /* XOR with the byte we search for. */ |
176 | eorl R(d0),R(d1) |
177 | |
178 | /* Add the magic value. We get carry bits reported for each byte |
179 | which is not C. */ |
180 | movel R(d3),R(d2) |
181 | addl R(d1),R(d2) |
182 | |
183 | /* Check the fourth carry bit before it is clobbered by the next |
184 | XOR. If it is not set we have a hit. */ |
185 | bcc L(L8) |
186 | |
187 | /* We are only interested in carry bits that change due to the |
188 | previous add, so remove original bits */ |
189 | eorl R(d1),R(d2) |
190 | |
191 | /* Now test for the other three overflow bits. |
192 | Set all non-carry bits. */ |
193 | orl R(d3),R(d2) |
194 | /* Add 1 to get zero if all carry bits were set. */ |
195 | addql #1,R(d2) |
196 | |
197 | /* If we don't get zero then at least one byte of the word equals |
198 | C. */ |
199 | bne L(L8) |
200 | |
201 | /* Next look for a NUL byte. |
202 | Restore original longword without reload. */ |
203 | eorl R(d0),R(d1) |
204 | /* Add the magic value. We get carry bits reported for each byte |
205 | which is not NUL. */ |
206 | movel R(d3),R(d2) |
207 | addl R(d1),R(d2) |
208 | |
209 | /* Check the fourth carry bit before it is clobbered by the next |
210 | XOR. If it is not set we have a hit, and return NULL. */ |
211 | bcc L(L3) |
212 | |
213 | /* We are only interested in carry bits that change due to the |
214 | previous add, so remove original bits */ |
215 | eorl R(d1),R(d2) |
216 | |
217 | /* Now test for the other three overflow bits. |
218 | Set all non-carry bits. */ |
219 | orl R(d3),R(d2) |
220 | /* Add 1 to get zero if all carry bits were set. */ |
221 | addql #1,R(d2) |
222 | |
223 | /* If we don't get zero then at least one byte of the word was NUL |
224 | and we return NULL. Otherwise continue with the next longword. */ |
225 | beq L(L2) |
226 | |
227 | L(L3:) |
228 | /* Return NULL. */ |
229 | clrl R(d0) |
230 | movel R(d0),R(a0) |
231 | movel MEM_POSTINC(sp),R(d3) |
232 | cfi_remember_state |
233 | cfi_adjust_cfa_offset (-4) |
234 | cfi_restore (R(d3)) |
235 | movel MEM_POSTINC(sp),R(d2) |
236 | cfi_adjust_cfa_offset (-4) |
237 | cfi_restore (R(d2)) |
238 | rts |
239 | |
240 | cfi_restore_state |
241 | L(L8:) |
242 | /* We have a hit. Check to see which byte it was. First |
243 | compensate for the autoincrement in the loop. */ |
244 | subql #4,R(a0) |
245 | |
246 | moveb MEM(a0),R(d1) |
247 | cmpb R(d0),R(d1) |
248 | beq L(L9) |
249 | tstb R(d1) |
250 | beq L(L3) |
251 | addql #1,R(a0) |
252 | |
253 | moveb MEM(a0),R(d1) |
254 | cmpb R(d0),R(d1) |
255 | beq L(L9) |
256 | tstb R(d1) |
257 | beq L(L3) |
258 | addql #1,R(a0) |
259 | |
260 | moveb MEM(a0),R(d1) |
261 | cmpb R(d0),R(d1) |
262 | beq L(L9) |
263 | tstb R(d1) |
264 | beq L(L3) |
265 | addql #1,R(a0) |
266 | |
267 | /* Otherwise the fourth byte must equal C. */ |
268 | L(L9:) |
269 | movel R(a0),R(d0) |
270 | movel MEM_POSTINC(sp),R(d3) |
271 | cfi_adjust_cfa_offset (-4) |
272 | cfi_restore (R(d3)) |
273 | movel MEM_POSTINC(sp),R(d2) |
274 | cfi_adjust_cfa_offset (-4) |
275 | cfi_restore (R(d2)) |
276 | rts |
277 | END(strchr) |
278 | |
279 | weak_alias (strchr, index) |
280 | libc_hidden_builtin_def (strchr) |
281 | |