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1da177e4 LT |
1 | /* |
2 | * arch/alpha/lib/stxcpy.S | |
3 | * Contributed by Richard Henderson (rth@tamu.edu) | |
4 | * | |
5 | * Copy a null-terminated string from SRC to DST. | |
6 | * | |
7 | * This is an internal routine used by strcpy, stpcpy, and strcat. | |
8 | * As such, it uses special linkage conventions to make implementation | |
9 | * of these public functions more efficient. | |
10 | * | |
11 | * On input: | |
12 | * t9 = return address | |
13 | * a0 = DST | |
14 | * a1 = SRC | |
15 | * | |
16 | * On output: | |
17 | * t12 = bitmask (with one bit set) indicating the last byte written | |
18 | * a0 = unaligned address of the last *word* written | |
19 | * | |
20 | * Furthermore, v0, a3-a5, t11, and t12 are untouched. | |
21 | */ | |
22 | ||
23 | #include <asm/regdef.h> | |
24 | ||
25 | .set noat | |
26 | .set noreorder | |
27 | ||
28 | .text | |
29 | ||
30 | /* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that | |
31 | doesn't like putting the entry point for a procedure somewhere in the | |
32 | middle of the procedure descriptor. Work around this by putting the | |
33 | aligned copy in its own procedure descriptor */ | |
34 | ||
35 | .ent stxcpy_aligned | |
36 | .align 3 | |
37 | stxcpy_aligned: | |
38 | .frame sp, 0, t9 | |
39 | .prologue 0 | |
40 | ||
41 | /* On entry to this basic block: | |
42 | t0 == the first destination word for masking back in | |
43 | t1 == the first source word. */ | |
44 | ||
45 | /* Create the 1st output word and detect 0's in the 1st input word. */ | |
46 | lda t2, -1 # e1 : build a mask against false zero | |
47 | mskqh t2, a1, t2 # e0 : detection in the src word | |
48 | mskqh t1, a1, t3 # e0 : | |
49 | ornot t1, t2, t2 # .. e1 : | |
50 | mskql t0, a1, t0 # e0 : assemble the first output word | |
51 | cmpbge zero, t2, t8 # .. e1 : bits set iff null found | |
52 | or t0, t3, t1 # e0 : | |
53 | bne t8, $a_eos # .. e1 : | |
54 | ||
55 | /* On entry to this basic block: | |
56 | t0 == the first destination word for masking back in | |
57 | t1 == a source word not containing a null. */ | |
58 | ||
59 | $a_loop: | |
60 | stq_u t1, 0(a0) # e0 : | |
61 | addq a0, 8, a0 # .. e1 : | |
62 | ldq_u t1, 0(a1) # e0 : | |
63 | addq a1, 8, a1 # .. e1 : | |
64 | cmpbge zero, t1, t8 # e0 (stall) | |
65 | beq t8, $a_loop # .. e1 (zdb) | |
66 | ||
67 | /* Take care of the final (partial) word store. | |
68 | On entry to this basic block we have: | |
69 | t1 == the source word containing the null | |
70 | t8 == the cmpbge mask that found it. */ | |
71 | $a_eos: | |
72 | negq t8, t6 # e0 : find low bit set | |
73 | and t8, t6, t12 # e1 (stall) | |
74 | ||
75 | /* For the sake of the cache, don't read a destination word | |
76 | if we're not going to need it. */ | |
77 | and t12, 0x80, t6 # e0 : | |
78 | bne t6, 1f # .. e1 (zdb) | |
79 | ||
80 | /* We're doing a partial word store and so need to combine | |
81 | our source and original destination words. */ | |
82 | ldq_u t0, 0(a0) # e0 : | |
83 | subq t12, 1, t6 # .. e1 : | |
84 | zapnot t1, t6, t1 # e0 : clear src bytes >= null | |
85 | or t12, t6, t8 # .. e1 : | |
86 | zap t0, t8, t0 # e0 : clear dst bytes <= null | |
87 | or t0, t1, t1 # e1 : | |
88 | ||
89 | 1: stq_u t1, 0(a0) # e0 : | |
90 | ret (t9) # .. e1 : | |
91 | ||
92 | .end stxcpy_aligned | |
93 | ||
94 | .align 3 | |
95 | .ent __stxcpy | |
96 | .globl __stxcpy | |
97 | __stxcpy: | |
98 | .frame sp, 0, t9 | |
99 | .prologue 0 | |
100 | ||
101 | /* Are source and destination co-aligned? */ | |
102 | xor a0, a1, t0 # e0 : | |
103 | unop # : | |
104 | and t0, 7, t0 # e0 : | |
105 | bne t0, $unaligned # .. e1 : | |
106 | ||
107 | /* We are co-aligned; take care of a partial first word. */ | |
108 | ldq_u t1, 0(a1) # e0 : load first src word | |
109 | and a0, 7, t0 # .. e1 : take care not to load a word ... | |
110 | addq a1, 8, a1 # e0 : | |
111 | beq t0, stxcpy_aligned # .. e1 : ... if we wont need it | |
112 | ldq_u t0, 0(a0) # e0 : | |
113 | br stxcpy_aligned # .. e1 : | |
114 | ||
115 | ||
116 | /* The source and destination are not co-aligned. Align the destination | |
117 | and cope. We have to be very careful about not reading too much and | |
118 | causing a SEGV. */ | |
119 | ||
120 | .align 3 | |
121 | $u_head: | |
122 | /* We know just enough now to be able to assemble the first | |
123 | full source word. We can still find a zero at the end of it | |
124 | that prevents us from outputting the whole thing. | |
125 | ||
126 | On entry to this basic block: | |
127 | t0 == the first dest word, for masking back in, if needed else 0 | |
128 | t1 == the low bits of the first source word | |
129 | t6 == bytemask that is -1 in dest word bytes */ | |
130 | ||
131 | ldq_u t2, 8(a1) # e0 : | |
132 | addq a1, 8, a1 # .. e1 : | |
133 | ||
134 | extql t1, a1, t1 # e0 : | |
135 | extqh t2, a1, t4 # e0 : | |
136 | mskql t0, a0, t0 # e0 : | |
137 | or t1, t4, t1 # .. e1 : | |
138 | mskqh t1, a0, t1 # e0 : | |
139 | or t0, t1, t1 # e1 : | |
140 | ||
141 | or t1, t6, t6 # e0 : | |
142 | cmpbge zero, t6, t8 # .. e1 : | |
143 | lda t6, -1 # e0 : for masking just below | |
144 | bne t8, $u_final # .. e1 : | |
145 | ||
146 | mskql t6, a1, t6 # e0 : mask out the bits we have | |
147 | or t6, t2, t2 # e1 : already extracted before | |
148 | cmpbge zero, t2, t8 # e0 : testing eos | |
149 | bne t8, $u_late_head_exit # .. e1 (zdb) | |
150 | ||
151 | /* Finally, we've got all the stupid leading edge cases taken care | |
152 | of and we can set up to enter the main loop. */ | |
153 | ||
154 | stq_u t1, 0(a0) # e0 : store first output word | |
155 | addq a0, 8, a0 # .. e1 : | |
156 | extql t2, a1, t0 # e0 : position ho-bits of lo word | |
157 | ldq_u t2, 8(a1) # .. e1 : read next high-order source word | |
158 | addq a1, 8, a1 # e0 : | |
159 | cmpbge zero, t2, t8 # .. e1 : | |
160 | nop # e0 : | |
161 | bne t8, $u_eos # .. e1 : | |
162 | ||
163 | /* Unaligned copy main loop. In order to avoid reading too much, | |
164 | the loop is structured to detect zeros in aligned source words. | |
165 | This has, unfortunately, effectively pulled half of a loop | |
166 | iteration out into the head and half into the tail, but it does | |
167 | prevent nastiness from accumulating in the very thing we want | |
168 | to run as fast as possible. | |
169 | ||
170 | On entry to this basic block: | |
171 | t0 == the shifted high-order bits from the previous source word | |
172 | t2 == the unshifted current source word | |
173 | ||
174 | We further know that t2 does not contain a null terminator. */ | |
175 | ||
176 | .align 3 | |
177 | $u_loop: | |
178 | extqh t2, a1, t1 # e0 : extract high bits for current word | |
179 | addq a1, 8, a1 # .. e1 : | |
180 | extql t2, a1, t3 # e0 : extract low bits for next time | |
181 | addq a0, 8, a0 # .. e1 : | |
182 | or t0, t1, t1 # e0 : current dst word now complete | |
183 | ldq_u t2, 0(a1) # .. e1 : load high word for next time | |
184 | stq_u t1, -8(a0) # e0 : save the current word | |
185 | mov t3, t0 # .. e1 : | |
186 | cmpbge zero, t2, t8 # e0 : test new word for eos | |
187 | beq t8, $u_loop # .. e1 : | |
188 | ||
189 | /* We've found a zero somewhere in the source word we just read. | |
190 | If it resides in the lower half, we have one (probably partial) | |
191 | word to write out, and if it resides in the upper half, we | |
192 | have one full and one partial word left to write out. | |
193 | ||
194 | On entry to this basic block: | |
195 | t0 == the shifted high-order bits from the previous source word | |
196 | t2 == the unshifted current source word. */ | |
197 | $u_eos: | |
198 | extqh t2, a1, t1 # e0 : | |
199 | or t0, t1, t1 # e1 : first (partial) source word complete | |
200 | ||
201 | cmpbge zero, t1, t8 # e0 : is the null in this first bit? | |
202 | bne t8, $u_final # .. e1 (zdb) | |
203 | ||
204 | $u_late_head_exit: | |
205 | stq_u t1, 0(a0) # e0 : the null was in the high-order bits | |
206 | addq a0, 8, a0 # .. e1 : | |
207 | extql t2, a1, t1 # e0 : | |
208 | cmpbge zero, t1, t8 # .. e1 : | |
209 | ||
210 | /* Take care of a final (probably partial) result word. | |
211 | On entry to this basic block: | |
212 | t1 == assembled source word | |
213 | t8 == cmpbge mask that found the null. */ | |
214 | $u_final: | |
215 | negq t8, t6 # e0 : isolate low bit set | |
216 | and t6, t8, t12 # e1 : | |
217 | ||
218 | and t12, 0x80, t6 # e0 : avoid dest word load if we can | |
219 | bne t6, 1f # .. e1 (zdb) | |
220 | ||
221 | ldq_u t0, 0(a0) # e0 : | |
222 | subq t12, 1, t6 # .. e1 : | |
223 | or t6, t12, t8 # e0 : | |
224 | zapnot t1, t6, t1 # .. e1 : kill source bytes >= null | |
225 | zap t0, t8, t0 # e0 : kill dest bytes <= null | |
226 | or t0, t1, t1 # e1 : | |
227 | ||
228 | 1: stq_u t1, 0(a0) # e0 : | |
229 | ret (t9) # .. e1 : | |
230 | ||
231 | /* Unaligned copy entry point. */ | |
232 | .align 3 | |
233 | $unaligned: | |
234 | ||
235 | ldq_u t1, 0(a1) # e0 : load first source word | |
236 | ||
237 | and a0, 7, t4 # .. e1 : find dest misalignment | |
238 | and a1, 7, t5 # e0 : find src misalignment | |
239 | ||
240 | /* Conditionally load the first destination word and a bytemask | |
241 | with 0xff indicating that the destination byte is sacrosanct. */ | |
242 | ||
243 | mov zero, t0 # .. e1 : | |
244 | mov zero, t6 # e0 : | |
245 | beq t4, 1f # .. e1 : | |
246 | ldq_u t0, 0(a0) # e0 : | |
247 | lda t6, -1 # .. e1 : | |
248 | mskql t6, a0, t6 # e0 : | |
249 | 1: | |
250 | subq a1, t4, a1 # .. e1 : sub dest misalignment from src addr | |
251 | ||
252 | /* If source misalignment is larger than dest misalignment, we need | |
253 | extra startup checks to avoid SEGV. */ | |
254 | ||
255 | cmplt t4, t5, t12 # e0 : | |
256 | beq t12, $u_head # .. e1 (zdb) | |
257 | ||
258 | lda t2, -1 # e1 : mask out leading garbage in source | |
259 | mskqh t2, t5, t2 # e0 : | |
260 | nop # e0 : | |
261 | ornot t1, t2, t3 # .. e1 : | |
262 | cmpbge zero, t3, t8 # e0 : is there a zero? | |
263 | beq t8, $u_head # .. e1 (zdb) | |
264 | ||
265 | /* At this point we've found a zero in the first partial word of | |
266 | the source. We need to isolate the valid source data and mask | |
267 | it into the original destination data. (Incidentally, we know | |
268 | that we'll need at least one byte of that original dest word.) */ | |
269 | ||
270 | ldq_u t0, 0(a0) # e0 : | |
271 | ||
272 | negq t8, t6 # .. e1 : build bitmask of bytes <= zero | |
273 | and t6, t8, t12 # e0 : | |
274 | and a1, 7, t5 # .. e1 : | |
275 | subq t12, 1, t6 # e0 : | |
276 | or t6, t12, t8 # e1 : | |
277 | srl t12, t5, t12 # e0 : adjust final null return value | |
278 | ||
279 | zapnot t2, t8, t2 # .. e1 : prepare source word; mirror changes | |
280 | and t1, t2, t1 # e1 : to source validity mask | |
281 | extql t2, a1, t2 # .. e0 : | |
282 | extql t1, a1, t1 # e0 : | |
283 | ||
284 | andnot t0, t2, t0 # .. e1 : zero place for source to reside | |
285 | or t0, t1, t1 # e1 : and put it there | |
286 | stq_u t1, 0(a0) # .. e0 : | |
287 | ret (t9) # e1 : | |
288 | ||
289 | .end __stxcpy |