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+/*
+ * arch/alpha/lib/stxcpy.S
+ * Contributed by Richard Henderson (rth@tamu.edu)
+ *
+ * Copy a null-terminated string from SRC to DST.
+ *
+ * This is an internal routine used by strcpy, stpcpy, and strcat.
+ * As such, it uses special linkage conventions to make implementation
+ * of these public functions more efficient.
+ *
+ * On input:
+ * t9 = return address
+ * a0 = DST
+ * a1 = SRC
+ *
+ * On output:
+ * t12 = bitmask (with one bit set) indicating the last byte written
+ * a0 = unaligned address of the last *word* written
+ *
+ * Furthermore, v0, a3-a5, t11, and t12 are untouched.
+ */
+
+#include <asm/regdef.h>
+
+ .set noat
+ .set noreorder
+
+ .text
+
+/* There is a problem with either gdb (as of 4.16) or gas (as of 2.7) that
+ doesn't like putting the entry point for a procedure somewhere in the
+ middle of the procedure descriptor. Work around this by putting the
+ aligned copy in its own procedure descriptor */
+
+ .ent stxcpy_aligned
+ .align 3
+stxcpy_aligned:
+ .frame sp, 0, t9
+ .prologue 0
+
+ /* On entry to this basic block:
+ t0 == the first destination word for masking back in
+ t1 == the first source word. */
+
+ /* Create the 1st output word and detect 0's in the 1st input word. */
+ lda t2, -1 # e1 : build a mask against false zero
+ mskqh t2, a1, t2 # e0 : detection in the src word
+ mskqh t1, a1, t3 # e0 :
+ ornot t1, t2, t2 # .. e1 :
+ mskql t0, a1, t0 # e0 : assemble the first output word
+ cmpbge zero, t2, t8 # .. e1 : bits set iff null found
+ or t0, t3, t1 # e0 :
+ bne t8, $a_eos # .. e1 :
+
+ /* On entry to this basic block:
+ t0 == the first destination word for masking back in
+ t1 == a source word not containing a null. */
+
+$a_loop:
+ stq_u t1, 0(a0) # e0 :
+ addq a0, 8, a0 # .. e1 :
+ ldq_u t1, 0(a1) # e0 :
+ addq a1, 8, a1 # .. e1 :
+ cmpbge zero, t1, t8 # e0 (stall)
+ beq t8, $a_loop # .. e1 (zdb)
+
+ /* Take care of the final (partial) word store.
+ On entry to this basic block we have:
+ t1 == the source word containing the null
+ t8 == the cmpbge mask that found it. */
+$a_eos:
+ negq t8, t6 # e0 : find low bit set
+ and t8, t6, t12 # e1 (stall)
+
+ /* For the sake of the cache, don't read a destination word
+ if we're not going to need it. */
+ and t12, 0x80, t6 # e0 :
+ bne t6, 1f # .. e1 (zdb)
+
+ /* We're doing a partial word store and so need to combine
+ our source and original destination words. */
+ ldq_u t0, 0(a0) # e0 :
+ subq t12, 1, t6 # .. e1 :
+ zapnot t1, t6, t1 # e0 : clear src bytes >= null
+ or t12, t6, t8 # .. e1 :
+ zap t0, t8, t0 # e0 : clear dst bytes <= null
+ or t0, t1, t1 # e1 :
+
+1: stq_u t1, 0(a0) # e0 :
+ ret (t9) # .. e1 :
+
+ .end stxcpy_aligned
+
+ .align 3
+ .ent __stxcpy
+ .globl __stxcpy
+__stxcpy:
+ .frame sp, 0, t9
+ .prologue 0
+
+ /* Are source and destination co-aligned? */
+ xor a0, a1, t0 # e0 :
+ unop # :
+ and t0, 7, t0 # e0 :
+ bne t0, $unaligned # .. e1 :
+
+ /* We are co-aligned; take care of a partial first word. */
+ ldq_u t1, 0(a1) # e0 : load first src word
+ and a0, 7, t0 # .. e1 : take care not to load a word ...
+ addq a1, 8, a1 # e0 :
+ beq t0, stxcpy_aligned # .. e1 : ... if we wont need it
+ ldq_u t0, 0(a0) # e0 :
+ br stxcpy_aligned # .. e1 :
+
+
+/* The source and destination are not co-aligned. Align the destination
+ and cope. We have to be very careful about not reading too much and
+ causing a SEGV. */
+
+ .align 3
+$u_head:
+ /* We know just enough now to be able to assemble the first
+ full source word. We can still find a zero at the end of it
+ that prevents us from outputting the whole thing.
+
+ On entry to this basic block:
+ t0 == the first dest word, for masking back in, if needed else 0
+ t1 == the low bits of the first source word
+ t6 == bytemask that is -1 in dest word bytes */
+
+ ldq_u t2, 8(a1) # e0 :
+ addq a1, 8, a1 # .. e1 :
+
+ extql t1, a1, t1 # e0 :
+ extqh t2, a1, t4 # e0 :
+ mskql t0, a0, t0 # e0 :
+ or t1, t4, t1 # .. e1 :
+ mskqh t1, a0, t1 # e0 :
+ or t0, t1, t1 # e1 :
+
+ or t1, t6, t6 # e0 :
+ cmpbge zero, t6, t8 # .. e1 :
+ lda t6, -1 # e0 : for masking just below
+ bne t8, $u_final # .. e1 :
+
+ mskql t6, a1, t6 # e0 : mask out the bits we have
+ or t6, t2, t2 # e1 : already extracted before
+ cmpbge zero, t2, t8 # e0 : testing eos
+ bne t8, $u_late_head_exit # .. e1 (zdb)
+
+ /* Finally, we've got all the stupid leading edge cases taken care
+ of and we can set up to enter the main loop. */
+
+ stq_u t1, 0(a0) # e0 : store first output word
+ addq a0, 8, a0 # .. e1 :
+ extql t2, a1, t0 # e0 : position ho-bits of lo word
+ ldq_u t2, 8(a1) # .. e1 : read next high-order source word
+ addq a1, 8, a1 # e0 :
+ cmpbge zero, t2, t8 # .. e1 :
+ nop # e0 :
+ bne t8, $u_eos # .. e1 :
+
+ /* Unaligned copy main loop. In order to avoid reading too much,
+ the loop is structured to detect zeros in aligned source words.
+ This has, unfortunately, effectively pulled half of a loop
+ iteration out into the head and half into the tail, but it does
+ prevent nastiness from accumulating in the very thing we want
+ to run as fast as possible.
+
+ On entry to this basic block:
+ t0 == the shifted high-order bits from the previous source word
+ t2 == the unshifted current source word
+
+ We further know that t2 does not contain a null terminator. */
+
+ .align 3
+$u_loop:
+ extqh t2, a1, t1 # e0 : extract high bits for current word
+ addq a1, 8, a1 # .. e1 :
+ extql t2, a1, t3 # e0 : extract low bits for next time
+ addq a0, 8, a0 # .. e1 :
+ or t0, t1, t1 # e0 : current dst word now complete
+ ldq_u t2, 0(a1) # .. e1 : load high word for next time
+ stq_u t1, -8(a0) # e0 : save the current word
+ mov t3, t0 # .. e1 :
+ cmpbge zero, t2, t8 # e0 : test new word for eos
+ beq t8, $u_loop # .. e1 :
+
+ /* We've found a zero somewhere in the source word we just read.
+ If it resides in the lower half, we have one (probably partial)
+ word to write out, and if it resides in the upper half, we
+ have one full and one partial word left to write out.
+
+ On entry to this basic block:
+ t0 == the shifted high-order bits from the previous source word
+ t2 == the unshifted current source word. */
+$u_eos:
+ extqh t2, a1, t1 # e0 :
+ or t0, t1, t1 # e1 : first (partial) source word complete
+
+ cmpbge zero, t1, t8 # e0 : is the null in this first bit?
+ bne t8, $u_final # .. e1 (zdb)
+
+$u_late_head_exit:
+ stq_u t1, 0(a0) # e0 : the null was in the high-order bits
+ addq a0, 8, a0 # .. e1 :
+ extql t2, a1, t1 # e0 :
+ cmpbge zero, t1, t8 # .. e1 :
+
+ /* Take care of a final (probably partial) result word.
+ On entry to this basic block:
+ t1 == assembled source word
+ t8 == cmpbge mask that found the null. */
+$u_final:
+ negq t8, t6 # e0 : isolate low bit set
+ and t6, t8, t12 # e1 :
+
+ and t12, 0x80, t6 # e0 : avoid dest word load if we can
+ bne t6, 1f # .. e1 (zdb)
+
+ ldq_u t0, 0(a0) # e0 :
+ subq t12, 1, t6 # .. e1 :
+ or t6, t12, t8 # e0 :
+ zapnot t1, t6, t1 # .. e1 : kill source bytes >= null
+ zap t0, t8, t0 # e0 : kill dest bytes <= null
+ or t0, t1, t1 # e1 :
+
+1: stq_u t1, 0(a0) # e0 :
+ ret (t9) # .. e1 :
+
+ /* Unaligned copy entry point. */
+ .align 3
+$unaligned:
+
+ ldq_u t1, 0(a1) # e0 : load first source word
+
+ and a0, 7, t4 # .. e1 : find dest misalignment
+ and a1, 7, t5 # e0 : find src misalignment
+
+ /* Conditionally load the first destination word and a bytemask
+ with 0xff indicating that the destination byte is sacrosanct. */
+
+ mov zero, t0 # .. e1 :
+ mov zero, t6 # e0 :
+ beq t4, 1f # .. e1 :
+ ldq_u t0, 0(a0) # e0 :
+ lda t6, -1 # .. e1 :
+ mskql t6, a0, t6 # e0 :
+1:
+ subq a1, t4, a1 # .. e1 : sub dest misalignment from src addr
+
+ /* If source misalignment is larger than dest misalignment, we need
+ extra startup checks to avoid SEGV. */
+
+ cmplt t4, t5, t12 # e0 :
+ beq t12, $u_head # .. e1 (zdb)
+
+ lda t2, -1 # e1 : mask out leading garbage in source
+ mskqh t2, t5, t2 # e0 :
+ nop # e0 :
+ ornot t1, t2, t3 # .. e1 :
+ cmpbge zero, t3, t8 # e0 : is there a zero?
+ beq t8, $u_head # .. e1 (zdb)
+
+ /* At this point we've found a zero in the first partial word of
+ the source. We need to isolate the valid source data and mask
+ it into the original destination data. (Incidentally, we know
+ that we'll need at least one byte of that original dest word.) */
+
+ ldq_u t0, 0(a0) # e0 :
+
+ negq t8, t6 # .. e1 : build bitmask of bytes <= zero
+ and t6, t8, t12 # e0 :
+ and a1, 7, t5 # .. e1 :
+ subq t12, 1, t6 # e0 :
+ or t6, t12, t8 # e1 :
+ srl t12, t5, t12 # e0 : adjust final null return value
+
+ zapnot t2, t8, t2 # .. e1 : prepare source word; mirror changes
+ and t1, t2, t1 # e1 : to source validity mask
+ extql t2, a1, t2 # .. e0 :
+ extql t1, a1, t1 # e0 :
+
+ andnot t0, t2, t0 # .. e1 : zero place for source to reside
+ or t0, t1, t1 # e1 : and put it there
+ stq_u t1, 0(a0) # .. e0 :
+ ret (t9) # e1 :
+
+ .end __stxcpy