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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/alpha/lib/ev6-stxcpy.S
downloadconfigs-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+/*
+ * arch/alpha/lib/ev6-stxcpy.S
+ * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
+ *
+ * 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.
+ *
+ * Much of the information about 21264 scheduling/coding comes from:
+ * Compiler Writer's Guide for the Alpha 21264
+ * abbreviated as 'CWG' in other comments here
+ * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
+ * Scheduling notation:
+ * E - either cluster
+ * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
+ * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
+ * Try not to change the actual algorithm if possible for consistency.
+ */
+
+#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 4
+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 # E : build a mask against false zero
+ mskqh t2, a1, t2 # U : detection in the src word (stall)
+ mskqh t1, a1, t3 # U :
+ ornot t1, t2, t2 # E : (stall)
+
+ mskql t0, a1, t0 # U : assemble the first output word
+ cmpbge zero, t2, t8 # E : bits set iff null found
+ or t0, t3, t1 # E : (stall)
+ bne t8, $a_eos # U : (stall)
+
+ /* On entry to this basic block:
+ t0 == the first destination word for masking back in
+ t1 == a source word not containing a null. */
+ /* Nops here to separate store quads from load quads */
+
+$a_loop:
+ stq_u t1, 0(a0) # L :
+ addq a0, 8, a0 # E :
+ nop
+ nop
+
+ ldq_u t1, 0(a1) # L : Latency=3
+ addq a1, 8, a1 # E :
+ cmpbge zero, t1, t8 # E : (3 cycle stall)
+ beq t8, $a_loop # U : (stall for t8)
+
+ /* Take care of the final (partial) word store.
+ On entry to this basic block we have:
+ t1 == the source word containing the null
+ t8 == the cmpbge mask that found it. */
+$a_eos:
+ negq t8, t6 # E : find low bit set
+ and t8, t6, t12 # E : (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 # E : (stall)
+ bne t6, 1f # U : (stall)
+
+ /* We're doing a partial word store and so need to combine
+ our source and original destination words. */
+ ldq_u t0, 0(a0) # L : Latency=3
+ subq t12, 1, t6 # E :
+ zapnot t1, t6, t1 # U : clear src bytes >= null (stall)
+ or t12, t6, t8 # E : (stall)
+
+ zap t0, t8, t0 # E : clear dst bytes <= null
+ or t0, t1, t1 # E : (stall)
+ nop
+ nop
+
+1: stq_u t1, 0(a0) # L :
+ ret (t9) # L0 : Latency=3
+ nop
+ nop
+
+ .end stxcpy_aligned
+
+ .align 4
+ .ent __stxcpy
+ .globl __stxcpy
+__stxcpy:
+ .frame sp, 0, t9
+ .prologue 0
+
+ /* Are source and destination co-aligned? */
+ xor a0, a1, t0 # E :
+ unop # E :
+ and t0, 7, t0 # E : (stall)
+ bne t0, $unaligned # U : (stall)
+
+ /* We are co-aligned; take care of a partial first word. */
+ ldq_u t1, 0(a1) # L : load first src word
+ and a0, 7, t0 # E : take care not to load a word ...
+ addq a1, 8, a1 # E :
+ beq t0, stxcpy_aligned # U : ... if we wont need it (stall)
+
+ ldq_u t0, 0(a0) # L :
+ br stxcpy_aligned # L0 : Latency=3
+ nop
+ nop
+
+
+/* The source and destination are not co-aligned. Align the destination
+ and cope. We have to be very careful about not reading too much and
+ causing a SEGV. */
+
+ .align 4
+$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) # L :
+ addq a1, 8, a1 # E :
+ extql t1, a1, t1 # U : (stall on a1)
+ extqh t2, a1, t4 # U : (stall on a1)
+
+ mskql t0, a0, t0 # U :
+ or t1, t4, t1 # E :
+ mskqh t1, a0, t1 # U : (stall on t1)
+ or t0, t1, t1 # E : (stall on t1)
+
+ or t1, t6, t6 # E :
+ cmpbge zero, t6, t8 # E : (stall)
+ lda t6, -1 # E : for masking just below
+ bne t8, $u_final # U : (stall)
+
+ mskql t6, a1, t6 # U : mask out the bits we have
+ or t6, t2, t2 # E : already extracted before (stall)
+ cmpbge zero, t2, t8 # E : testing eos (stall)
+ bne t8, $u_late_head_exit # U : (stall)
+
+ /* 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) # L : store first output word
+ addq a0, 8, a0 # E :
+ extql t2, a1, t0 # U : position ho-bits of lo word
+ ldq_u t2, 8(a1) # U : read next high-order source word
+
+ addq a1, 8, a1 # E :
+ cmpbge zero, t2, t8 # E : (stall for t2)
+ nop # E :
+ bne t8, $u_eos # U : (stall)
+
+ /* Unaligned copy main loop. In order to avoid reading too much,
+ the loop is structured to detect zeros in aligned source words.
+ This has, unfortunately, effectively pulled half of a loop
+ iteration out into the head and half into the tail, but it does
+ prevent nastiness from accumulating in the very thing we want
+ to run as fast as possible.
+
+ On entry to this basic block:
+ t0 == the shifted high-order bits from the previous source word
+ t2 == the unshifted current source word
+
+ We further know that t2 does not contain a null terminator. */
+
+ .align 3
+$u_loop:
+ extqh t2, a1, t1 # U : extract high bits for current word
+ addq a1, 8, a1 # E : (stall)
+ extql t2, a1, t3 # U : extract low bits for next time (stall)
+ addq a0, 8, a0 # E :
+
+ or t0, t1, t1 # E : current dst word now complete
+ ldq_u t2, 0(a1) # L : Latency=3 load high word for next time
+ stq_u t1, -8(a0) # L : save the current word (stall)
+ mov t3, t0 # E :
+
+ cmpbge zero, t2, t8 # E : test new word for eos
+ beq t8, $u_loop # U : (stall)
+ nop
+ nop
+
+ /* We've found a zero somewhere in the source word we just read.
+ If it resides in the lower half, we have one (probably partial)
+ word to write out, and if it resides in the upper half, we
+ have one full and one partial word left to write out.
+
+ On entry to this basic block:
+ t0 == the shifted high-order bits from the previous source word
+ t2 == the unshifted current source word. */
+$u_eos:
+ extqh t2, a1, t1 # U :
+ or t0, t1, t1 # E : first (partial) source word complete (stall)
+ cmpbge zero, t1, t8 # E : is the null in this first bit? (stall)
+ bne t8, $u_final # U : (stall)
+
+$u_late_head_exit:
+ stq_u t1, 0(a0) # L : the null was in the high-order bits
+ addq a0, 8, a0 # E :
+ extql t2, a1, t1 # U :
+ cmpbge zero, t1, t8 # E : (stall)
+
+ /* 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. */
+$u_final:
+ negq t8, t6 # E : isolate low bit set
+ and t6, t8, t12 # E : (stall)
+ and t12, 0x80, t6 # E : avoid dest word load if we can (stall)
+ bne t6, 1f # U : (stall)
+
+ ldq_u t0, 0(a0) # E :
+ subq t12, 1, t6 # E :
+ or t6, t12, t8 # E : (stall)
+ zapnot t1, t6, t1 # U : kill source bytes >= null (stall)
+
+ zap t0, t8, t0 # U : kill dest bytes <= null (2 cycle data stall)
+ or t0, t1, t1 # E : (stall)
+ nop
+ nop
+
+1: stq_u t1, 0(a0) # L :
+ ret (t9) # L0 : Latency=3
+ nop
+ nop
+
+ /* Unaligned copy entry point. */
+ .align 4
+$unaligned:
+
+ ldq_u t1, 0(a1) # L : load first source word
+ and a0, 7, t4 # E : find dest misalignment
+ and a1, 7, t5 # E : find src misalignment
+ /* Conditionally load the first destination word and a bytemask
+ with 0xff indicating that the destination byte is sacrosanct. */
+ mov zero, t0 # E :
+
+ mov zero, t6 # E :
+ beq t4, 1f # U :
+ ldq_u t0, 0(a0) # L :
+ lda t6, -1 # E :
+
+ mskql t6, a0, t6 # U :
+ nop
+ nop
+ nop
+1:
+ subq a1, t4, a1 # E : 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 # E :
+ beq t12, $u_head # U :
+ lda t2, -1 # E : mask out leading garbage in source
+
+ mskqh t2, t5, t2 # U :
+ ornot t1, t2, t3 # E : (stall)
+ cmpbge zero, t3, t8 # E : is there a zero? (stall)
+ beq t8, $u_head # U : (stall)
+
+ /* 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) # L :
+ negq t8, t6 # E : build bitmask of bytes <= zero
+ and t6, t8, t12 # E : (stall)
+ and a1, 7, t5 # E :
+
+ subq t12, 1, t6 # E :
+ or t6, t12, t8 # E : (stall)
+ srl t12, t5, t12 # U : adjust final null return value
+ zapnot t2, t8, t2 # U : prepare source word; mirror changes (stall)
+
+ and t1, t2, t1 # E : to source validity mask
+ extql t2, a1, t2 # U :
+ extql t1, a1, t1 # U : (stall)
+ andnot t0, t2, t0 # .. e1 : zero place for source to reside (stall)
+
+ or t0, t1, t1 # e1 : and put it there
+ stq_u t1, 0(a0) # .. e0 : (stall)
+ ret (t9) # e1 :
+ nop
+
+ .end __stxcpy
+