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alpha: Fix end-of-count checks in strncmp
This routine suffered a similar problem as stxncpy in needing to bias a potentially very large unsigned number with wraparound. This exposed a secondary problem where we didn't properly handle end-of-count condition for the second string input resulting in stratcliff failures.
This commit is contained in:
Richard Henderson
parent
8e2f4e971f
commit
d8cbc13ab6
@ -1,5 +1,8 @@
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2012-06-06 Richard Henderson <rth@twiddle.net>
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* sysdeps/alpha/strncmp.S: Bound count to LONG_MAX at startup.
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Re-organize checks vs s2 end-of-count.
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[BZ #13718]
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* sysdeps/alpha/stxncmp.S: Bound count to LONG_MAX at startup.
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* sysdeps/alpha/alphaev6/stxncmp.S: Likewise.
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@ -1,4 +1,4 @@
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/* Copyright (C) 1996, 1997, 2003 Free Software Foundation, Inc.
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/* Copyright (C) 1996-2012 Free Software Foundation, Inc.
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Contributed by Richard Henderson (rth@tamu.edu)
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This file is part of the GNU C Library.
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@ -23,6 +23,15 @@
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.set noat
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.set noreorder
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/* EV6 only predicts one branch per octaword. We'll use these to push
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subsequent branches back to the next bundle. This will generally add
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a fetch+decode cycle to older machines, so skip in that case. */
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#ifdef __alpha_fix__
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# define ev6_unop unop
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#else
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# define ev6_unop
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#endif
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.text
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ENTRY(strncmp)
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@ -35,128 +44,140 @@ ENTRY(strncmp)
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.prologue 0
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#endif
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xor a0, a1, t2 # e0 : are s1 and s2 co-aligned?
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beq a2, $zerolength # .. e1 :
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ldq_u t0, 0(a0) # e0 : give cache time to catch up
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ldq_u t1, 0(a1) # .. e1 :
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and t2, 7, t2 # e0 :
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and a0, 7, t4 # .. e1 : find s1 misalignment
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lda t3, -1 # e0 :
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addq a2, t4, a2 # .. e1 : bias count by s1 misalignment
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and a2, 7, t10 # e1 : ofs of last byte in last word
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srl a2, 3, a2 # .. e0 : remaining full words in count
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and a1, 7, t5 # e0 : find s2 misalignment
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bne t2, $unaligned # .. e1 :
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xor a0, a1, t2 # are s1 and s2 co-aligned?
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beq a2, $zerolength
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ldq_u t0, 0(a0) # load asap to give cache time to catch up
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ldq_u t1, 0(a1)
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lda t3, -1
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and t2, 7, t2
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srl t3, 1, t6
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and a0, 7, t4 # find s1 misalignment
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and a1, 7, t5 # find s2 misalignment
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cmovlt a2, t6, a2 # bound neg count to LONG_MAX
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addq a1, a2, a3 # s2+count
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addq a2, t4, a2 # bias count by s1 misalignment
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and a2, 7, t10 # ofs of last byte in s1 last word
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srl a2, 3, a2 # remaining full words in s1 count
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bne t2, $unaligned
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/* On entry to this basic block:
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t0 == the first word of s1.
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t1 == the first word of s2.
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t3 == -1. */
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$aligned:
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mskqh t3, a1, t3 # e0 : mask off leading garbage
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nop # .. e1 :
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ornot t1, t3, t1 # e0 :
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ornot t0, t3, t0 # .. e1 :
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cmpbge zero, t1, t7 # e0 : bits set iff null found
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beq a2, $eoc # .. e1 : check end of count
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unop # e0 :
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bne t7, $eos # .. e1 :
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unop # e0 :
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beq t10, $ant_loop # .. e1 :
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mskqh t3, a1, t8 # mask off leading garbage
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ornot t1, t8, t1
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ornot t0, t8, t0
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cmpbge zero, t1, t7 # bits set iff null found
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beq a2, $eoc # check end of count
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bne t7, $eos
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beq t10, $ant_loop
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/* Aligned compare main loop.
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On entry to this basic block:
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t0 == an s1 word.
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t1 == an s2 word not containing a null. */
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.align 4
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$a_loop:
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xor t0, t1, t2 # e0 :
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bne t2, $wordcmp # .. e1 (zdb)
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ldq_u t1, 8(a1) # e0 :
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ldq_u t0, 8(a0) # .. e1 :
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subq a2, 1, a2 # e0 :
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addq a1, 8, a1 # .. e1 :
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addq a0, 8, a0 # e0 :
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beq a2, $eoc # .. e1 :
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cmpbge zero, t1, t7 # e0 :
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beq t7, $a_loop # .. e1 :
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unop # e0 :
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br $eos # .. e1 :
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br $eos
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/* Alternate aligned compare loop, for when there's no trailing
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bytes on the count. We have to avoid reading too much data. */
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.align 4
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$ant_loop:
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xor t0, t1, t2 # e0 :
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ev6_unop
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ev6_unop
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bne t2, $wordcmp # .. e1 (zdb)
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subq a2, 1, a2 # e0 :
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beq a2, $zerolength # .. e1 :
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ldq_u t1, 8(a1) # e0 :
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ldq_u t0, 8(a0) # .. e1 :
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addq a1, 8, a1 # e0 :
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addq a0, 8, a0 # .. e1 :
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cmpbge zero, t1, t7 # e0 :
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beq t7, $ant_loop # .. e1 :
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unop # e0 :
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br $eos # .. e1 :
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br $eos
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/* The two strings are not co-aligned. Align s1 and cope. */
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/* On entry to this basic block:
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t0 == the first word of s1.
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t1 == the first word of s2.
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t3 == -1.
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t4 == misalignment of s1.
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t5 == misalignment of s2.
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t10 == misalignment of s1 end. */
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.align 4
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$unaligned:
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subq a1, t4, a1 # e0 :
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unop # :
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/* If s2 misalignment is larger than s2 misalignment, we need
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/* If s1 misalignment is larger than s2 misalignment, we need
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extra startup checks to avoid SEGV. */
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subq a1, t4, a1 # adjust s2 for s1 misalignment
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cmpult t4, t5, t9
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subq a3, 1, a3 # last byte of s2
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bic a1, 7, t8
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mskqh t3, t5, t7 # mask garbage in s2
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subq a3, t8, a3
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ornot t1, t7, t7
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srl a3, 3, a3 # remaining full words in s2 count
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beq t9, $u_head
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cmplt t4, t5, t8 # .. e1 :
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beq t8, $u_head # e1 :
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/* Failing that, we need to look for both eos and eoc within the
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first word of s2. If we find either, we can continue by
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pretending that the next word of s2 is all zeros. */
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lda t2, 0 # next = zero
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cmpeq a3, 0, t8 # eoc in the first word of s2?
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cmpbge zero, t7, t7 # eos in the first word of s2?
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or t7, t8, t8
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bne t8, $u_head_nl
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mskqh t3, t5, t3 # e0 :
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ornot t1, t3, t3 # e0 :
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cmpbge zero, t3, t7 # e1 : is there a zero?
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beq t7, $u_head # e1 :
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/* We've found a zero in the first partial word of s2. Align
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our current s1 and s2 words and compare what we've got. */
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extql t1, t5, t1 # e0 :
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lda t3, -1 # .. e1 :
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insql t1, a0, t1 # e0 :
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mskqh t3, a0, t3 # e0 :
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ornot t1, t3, t1 # e0 :
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ornot t0, t3, t0 # .. e1 :
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cmpbge zero, t1, t7 # e0 : find that zero again
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beq a2, $eoc # .. e1 : and finish up
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br $eos # e1 :
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.align 3
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$u_head:
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/* We know just enough now to be able to assemble the first
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full word of s2. We can still find a zero at the end of it.
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On entry to this basic block:
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t0 == first word of s1
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t1 == first partial word of s2. */
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ldq_u t2, 8(a1) # e0 : load second partial s2 word
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lda t3, -1 # .. e1 : create leading garbage mask
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extql t1, a1, t1 # e0 : create first s2 word
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mskqh t3, a0, t3 # e0 :
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extqh t2, a1, t4 # e0 :
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ornot t0, t3, t0 # .. e1 : kill s1 garbage
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or t1, t4, t1 # e0 : s2 word now complete
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ornot t1, t3, t1 # e1 : kill s2 garbage
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cmpbge zero, t0, t7 # e0 : find zero in first s1 word
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beq a2, $eoc # .. e1 :
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lda t3, -1 # e0 :
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bne t7, $eos # .. e1 :
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subq a2, 1, a2 # e0 :
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xor t0, t1, t4 # .. e1 : compare aligned words
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mskql t3, a1, t3 # e0 : mask out s2[1] bits we have seen
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bne t4, $wordcmp # .. e1 :
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or t2, t3, t3 # e0 :
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cmpbge zero, t3, t7 # e1 : find zero in high bits of s2[1]
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bne t7, $u_final # e1 :
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t1 == first partial word of s2.
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t3 == -1.
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t10 == ofs of last byte in s1 last word.
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t11 == ofs of last byte in s2 last word. */
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$u_head:
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ldq_u t2, 8(a1) # load second partial s2 word
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subq a3, 1, a3
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$u_head_nl:
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extql t1, a1, t1 # create first s2 word
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mskqh t3, a0, t8
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extqh t2, a1, t4
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ornot t0, t8, t0 # kill s1 garbage
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or t1, t4, t1 # s2 word now complete
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cmpbge zero, t0, t7 # find eos in first s1 word
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ornot t1, t8, t1 # kill s2 garbage
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beq a2, $eoc
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subq a2, 1, a2
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bne t7, $eos
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mskql t3, a1, t8 # mask out s2[1] bits we have seen
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xor t0, t1, t4 # compare aligned words
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or t2, t8, t8
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bne t4, $wordcmp
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cmpbge zero, t8, t7 # eos in high bits of s2[1]?
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cmpeq a3, 0, t8 # eoc in s2[1]?
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or t7, t8, t7
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bne t7, $u_final
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/* Unaligned copy main loop. In order to avoid reading too much,
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the loop is structured to detect zeros in aligned words from s2.
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@ -166,43 +187,54 @@ $u_head:
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to run as fast as possible.
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On entry to this basic block:
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t2 == the unshifted low-bits from the next s2 word. */
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.align 3
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t2 == the unshifted low-bits from the next s2 word.
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t10 == ofs of last byte in s1 last word.
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t11 == ofs of last byte in s2 last word. */
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.align 4
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$u_loop:
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extql t2, a1, t3 # e0 :
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ldq_u t2, 16(a1) # .. e1 : load next s2 high bits
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ldq_u t0, 8(a0) # e0 : load next s1 word
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addq a1, 8, a1 # .. e1 :
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addq a0, 8, a0 # e0 :
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nop # .. e1 :
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subq a3, 1, a3 # .. e1 :
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extqh t2, a1, t1 # e0 :
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cmpbge zero, t0, t7 # .. e1 : find zero in current s1 word
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cmpbge zero, t0, t7 # .. e1 : eos in current s1 word
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or t1, t3, t1 # e0 :
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beq a2, $eoc # .. e1 : check for end of count
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beq a2, $eoc # .. e1 : eoc in current s1 word
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subq a2, 1, a2 # e0 :
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cmpbge zero, t2, t4 # .. e1 : eos in s2[1]
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xor t0, t1, t3 # e0 : compare the words
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ev6_unop
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ev6_unop
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bne t7, $eos # .. e1 :
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xor t0, t1, t4 # e0 : compare the words
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bne t4, $wordcmp # .. e1 (zdb)
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cmpbge zero, t2, t4 # e0 : find zero in next low bits
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cmpeq a3, 0, t5 # e0 : eoc in s2[1]
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ev6_unop
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ev6_unop
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bne t3, $wordcmp # .. e1 :
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or t4, t5, t4 # e0 : eos or eoc in s2[1].
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beq t4, $u_loop # .. e1 (zdb)
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/* We've found a zero in the low bits of the last s2 word. Get
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the next s1 word and align them. */
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.align 3
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$u_final:
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ldq_u t0, 8(a0) # e1 :
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extql t2, a1, t1 # .. e0 :
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cmpbge zero, t1, t7 # e0 :
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bne a2, $eos # .. e1 :
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ldq_u t0, 8(a0)
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extql t2, a1, t1
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cmpbge zero, t1, t7
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bne a2, $eos
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/* We've hit end of count. Zero everything after the count
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and compare whats left. */
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.align 3
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$eoc:
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mskql t0, t10, t0
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mskql t1, t10, t1
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unop
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cmpbge zero, t1, t7
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/* We've found a zero somewhere in a word we just read.
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@ -210,32 +242,31 @@ $eoc:
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t0 == s1 word
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t1 == s2 word
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t7 == cmpbge mask containing the zero. */
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.align 3
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$eos:
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negq t7, t6 # e0 : create bytemask of valid data
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and t6, t7, t8 # e1 :
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subq t8, 1, t6 # e0 :
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or t6, t8, t7 # e1 :
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zapnot t0, t7, t0 # e0 : kill the garbage
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zapnot t1, t7, t1 # .. e1 :
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xor t0, t1, v0 # e0 : and compare
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beq v0, $done # .. e1 :
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negq t7, t6 # create bytemask of valid data
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and t6, t7, t8
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subq t8, 1, t6
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or t6, t8, t7
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zapnot t0, t7, t0 # kill the garbage
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zapnot t1, t7, t1
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xor t0, t1, v0 # ... and compare
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beq v0, $done
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/* Here we have two differing co-aligned words in t0 & t1.
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Bytewise compare them and return (t0 > t1 ? 1 : -1). */
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.align 3
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$wordcmp:
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cmpbge t0, t1, t2 # e0 : comparison yields bit mask of ge
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cmpbge t1, t0, t3 # .. e1 :
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xor t2, t3, t0 # e0 : bits set iff t0/t1 bytes differ
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negq t0, t1 # e1 : clear all but least bit
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and t0, t1, t0 # e0 :
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lda v0, -1 # .. e1 :
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and t0, t2, t1 # e0 : was bit set in t0 > t1?
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cmovne t1, 1, v0 # .. e1 (zdb)
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cmpbge t0, t1, t2 # comparison yields bit mask of ge
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cmpbge t1, t0, t3
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xor t2, t3, t0 # bits set iff t0/t1 bytes differ
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negq t0, t1 # clear all but least bit
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and t0, t1, t0
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lda v0, -1
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and t0, t2, t1 # was bit set in t0 > t1?
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cmovne t1, 1, v0
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$done:
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ret # e1 :
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ret
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.align 3
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$zerolength:
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