2 * arch/alpha/lib/ev6-stxncpy.S
3 * 21264 version contributed by Rick Gorton <rick.gorton@api-networks.com>
5 * Copy no more than COUNT bytes of the null-terminated string from
8 * This is an internal routine used by strncpy, stpncpy, and strncat.
9 * As such, it uses special linkage conventions to make implementation
10 * of these public functions more efficient.
18 * Furthermore, COUNT may not be zero.
21 * t0 = last word written
22 * t10 = bitmask (with one bit set) indicating the byte position of
23 * the end of the range specified by COUNT
24 * t12 = bitmask (with one bit set) indicating the last byte written
25 * a0 = unaligned address of the last *word* written
26 * a2 = the number of full words left in COUNT
28 * Furthermore, v0, a3-a5, t11, and $at are untouched.
30 * Much of the information about 21264 scheduling/coding comes from:
31 * Compiler Writer's Guide for the Alpha 21264
32 * abbreviated as 'CWG' in other comments here
33 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
34 * Scheduling notation:
36 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
37 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
38 * Try not to change the actual algorithm if possible for consistency.
41 #include <asm/regdef.h>
56 /* On entry to this basic block:
57 t0 == the first destination word for masking back in
58 t1 == the first source word. */
60 /* Create the 1st output word and detect 0's in the 1st input word. */
61 lda t2, -1 # E : build a mask against false zero
62 mskqh t2, a1, t2 # U : detection in the src word (stall)
63 mskqh t1, a1, t3 # U :
64 ornot t1, t2, t2 # E : (stall)
66 mskql t0, a1, t0 # U : assemble the first output word
67 cmpbge zero, t2, t8 # E : bits set iff null found
68 or t0, t3, t0 # E : (stall)
76 /* On entry to this basic block:
77 t0 == a source word not containing a null. */
81 * separate store quads from load quads
82 * limit of 1 bcond/quad to permit training
92 cmpbge zero, t0, t8 # E :
100 /* Take care of the final (partial) word store. At this point
101 the end-of-count bit is set in t8 iff it applies.
103 On entry to this basic block we have:
104 t0 == the source word containing the null
105 t8 == the cmpbge mask that found it. */
108 negq t8, t12 # E : find low bit set
109 and t8, t12, t12 # E : (stall)
110 /* For the sake of the cache, don't read a destination word
111 if we're not going to need it. */
112 and t12, 0x80, t6 # E : (stall)
113 bne t6, 1f # U : (stall)
115 /* We're doing a partial word store and so need to combine
116 our source and original destination words. */
117 ldq_u t1, 0(a0) # L :
118 subq t12, 1, t6 # E :
119 or t12, t6, t8 # E : (stall)
120 zapnot t0, t8, t0 # U : clear src bytes > null (stall)
122 zap t1, t8, t1 # .. e1 : clear dst bytes <= null
123 or t0, t1, t0 # e1 : (stall)
127 1: stq_u t0, 0(a0) # L :
128 ret (t9) # L0 : Latency=3
132 /* Add the end-of-count bit to the eos detection bitmask. */
135 br $a_eos # L0 : Latency=3
148 /* Are source and destination co-aligned? */
150 and a0, 7, t0 # E : find dest misalignment
151 and t1, 7, t1 # E : (stall)
152 addq a2, t0, a2 # E : bias count by dest misalignment (stall)
155 and a2, 7, t2 # E : (stall)
156 srl a2, 3, a2 # U : a2 = loop counter = (count - 1)/8 (stall)
157 addq zero, 1, t10 # E :
159 sll t10, t2, t10 # U : t10 = bitmask of last count byte
160 bne t1, $unaligned # U :
161 /* We are co-aligned; take care of a partial first word. */
162 ldq_u t1, 0(a1) # L : load first src word
165 beq t0, stxncpy_aligned # U : avoid loading dest word if not needed
166 ldq_u t0, 0(a0) # L :
170 br stxncpy_aligned # .. e1 :
177 /* The source and destination are not co-aligned. Align the destination
178 and cope. We have to be very careful about not reading too much and
183 /* We know just enough now to be able to assemble the first
184 full source word. We can still find a zero at the end of it
185 that prevents us from outputting the whole thing.
187 On entry to this basic block:
188 t0 == the first dest word, unmasked
189 t1 == the shifted low bits of the first source word
190 t6 == bytemask that is -1 in dest word bytes */
192 ldq_u t2, 8(a1) # L : Latency=3 load second src word
194 mskql t0, a0, t0 # U : mask trailing garbage in dst
195 extqh t2, a1, t4 # U : (3 cycle stall on t2)
197 or t1, t4, t1 # E : first aligned src word complete (stall)
198 mskqh t1, a0, t1 # U : mask leading garbage in src (stall)
199 or t0, t1, t0 # E : first output word complete (stall)
200 or t0, t6, t6 # E : mask original data for zero test (stall)
202 cmpbge zero, t6, t8 # E :
203 beq a2, $u_eocfin # U :
207 bne t8, $u_final # U :
208 mskql t6, a1, t6 # U : mask out bits already seen
209 stq_u t0, 0(a0) # L : store first output word
210 or t6, t2, t2 # E : (stall)
212 cmpbge zero, t2, t8 # E : find nulls in second partial
215 bne t8, $u_late_head_exit # U :
217 /* Finally, we've got all the stupid leading edge cases taken care
218 of and we can set up to enter the main loop. */
219 extql t2, a1, t1 # U : position hi-bits of lo word
221 ldq_u t2, 8(a1) # L : read next high-order source word
224 extqh t2, a1, t0 # U : position lo-bits of hi word (stall)
225 cmpbge zero, t2, t8 # E :
229 /* Unaligned copy main loop. In order to avoid reading too much,
230 the loop is structured to detect zeros in aligned source words.
231 This has, unfortunately, effectively pulled half of a loop
232 iteration out into the head and half into the tail, but it does
233 prevent nastiness from accumulating in the very thing we want
234 to run as fast as possible.
236 On entry to this basic block:
237 t0 == the shifted low-order bits from the current source word
238 t1 == the shifted high-order bits from the previous source word
239 t2 == the unshifted current source word
241 We further know that t2 does not contain a null terminator. */
245 or t0, t1, t0 # E : current dst word now complete
246 subq a2, 1, a2 # E : decrement word count
247 extql t2, a1, t1 # U : extract low bits for next time
250 stq_u t0, -8(a0) # U : save the current word
252 ldq_u t2, 8(a1) # U : Latency=3 load high word for next time
255 extqh t2, a1, t0 # U : extract low bits (2 cycle stall)
256 cmpbge zero, t2, t8 # E : test new word for eos
258 beq t8, $u_loop # U :
260 /* We've found a zero somewhere in the source word we just read.
261 If it resides in the lower half, we have one (probably partial)
262 word to write out, and if it resides in the upper half, we
263 have one full and one partial word left to write out.
265 On entry to this basic block:
266 t0 == the shifted low-order bits from the current source word
267 t1 == the shifted high-order bits from the previous source word
268 t2 == the unshifted current source word. */
270 or t0, t1, t0 # E : first (partial) source word complete
272 cmpbge zero, t0, t8 # E : is the null in this first bit? (stall)
273 bne t8, $u_final # U : (stall)
275 stq_u t0, 0(a0) # L : the null was in the high-order bits
281 extql t2, a1, t0 # U :
282 cmpbge zero, t0, t8 # E :
283 or t8, t10, t6 # E : (stall)
284 cmoveq a2, t6, t8 # E : Latency=2, extra map slot (stall)
286 /* Take care of a final (probably partial) result word.
287 On entry to this basic block:
288 t0 == assembled source word
289 t8 == cmpbge mask that found the null. */
291 negq t8, t6 # E : isolate low bit set
292 and t6, t8, t12 # E : (stall)
293 and t12, 0x80, t6 # E : avoid dest word load if we can (stall)
294 bne t6, 1f # U : (stall)
296 ldq_u t1, 0(a0) # L :
297 subq t12, 1, t6 # E :
298 or t6, t12, t8 # E : (stall)
299 zapnot t0, t8, t0 # U : kill source bytes > null
301 zap t1, t8, t1 # U : kill dest bytes <= null
302 or t0, t1, t0 # E : (stall)
306 1: stq_u t0, 0(a0) # L :
307 ret (t9) # L0 : Latency=3
309 /* Got to end-of-count before end of string.
310 On entry to this basic block:
311 t1 == the shifted high-order bits from the previous source word */
313 and a1, 7, t6 # E : avoid final load if possible
314 sll t10, t6, t6 # U : (stall)
315 and t6, 0xff, t6 # E : (stall)
316 bne t6, 1f # U : (stall)
318 ldq_u t2, 8(a1) # L : load final src word
320 extqh t2, a1, t0 # U : extract low bits for last word (stall)
321 or t1, t0, t1 # E : (stall)
323 1: cmpbge zero, t1, t8 # E :
326 $u_eocfin: # end-of-count, final word
328 br $u_final # L0 : Latency=3
330 /* Unaligned copy entry point. */
334 ldq_u t1, 0(a1) # L : load first source word
335 and a0, 7, t4 # E : find dest misalignment
336 and a1, 7, t5 # E : find src misalignment
337 /* Conditionally load the first destination word and a bytemask
338 with 0xff indicating that the destination byte is sacrosanct. */
343 ldq_u t0, 0(a0) # L :
346 mskql t6, a0, t6 # U :
349 subq a1, t4, a1 # E : sub dest misalignment from src addr
351 /* If source misalignment is larger than dest misalignment, we need
352 extra startup checks to avoid SEGV. */
354 1: cmplt t4, t5, t12 # E :
355 extql t1, a1, t1 # U : shift src into place
356 lda t2, -1 # E : for creating masks later
357 beq t12, $u_head # U : (stall)
359 extql t2, a1, t2 # U :
360 cmpbge zero, t1, t8 # E : is there a zero?
361 andnot t2, t6, t2 # E : dest mask for a single word copy
362 or t8, t10, t5 # E : test for end-of-count too
364 cmpbge zero, t2, t3 # E :
365 cmoveq a2, t5, t8 # E : Latency=2, extra map slot
366 nop # E : keep with cmoveq
367 andnot t8, t3, t8 # E : (stall)
369 beq t8, $u_head # U :
370 /* At this point we've found a zero in the first partial word of
371 the source. We need to isolate the valid source data and mask
372 it into the original destination data. (Incidentally, we know
373 that we'll need at least one byte of that original dest word.) */
374 ldq_u t0, 0(a0) # L :
375 negq t8, t6 # E : build bitmask of bytes <= zero
376 mskqh t1, t4, t1 # U :
378 and t6, t8, t12 # E :
379 subq t12, 1, t6 # E : (stall)
380 or t6, t12, t8 # E : (stall)
381 zapnot t2, t8, t2 # U : prepare source word; mirror changes (stall)
383 zapnot t1, t8, t1 # U : to source validity mask
384 andnot t0, t2, t0 # E : zero place for source to reside
385 or t0, t1, t0 # E : and put it there (stall both t0, t1)
386 stq_u t0, 0(a0) # L : (stall)
388 ret (t9) # L0 : Latency=3