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-/* Copyright (C) 1996-2023 Free Software Foundation, Inc.
- This file is part of the GNU C Library.
-
- The GNU C Library is free software; you can redistribute it and/or
- modify it under the terms of the GNU Lesser General Public
- License as published by the Free Software Foundation; either
- version 2.1 of the License, or (at your option) any later version.
-
- The GNU C Library is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public
- License along with the GNU C Library. If not, see
- <https://www.gnu.org/licenses/>. */
-
-/* Bytewise compare two null-terminated strings of length no longer than N. */
-
-#include <sysdep.h>
-
- .set noat
- .set noreorder
-
-/* EV6 only predicts one branch per octaword. We'll use these to push
- subsequent branches back to the next bundle. This will generally add
- a fetch+decode cycle to older machines, so skip in that case. */
-#ifdef __alpha_fix__
-# define ev6_unop unop
-#else
-# define ev6_unop
-#endif
-
- .text
-
-ENTRY(strncmp)
-#ifdef PROF
- ldgp gp, 0(pv)
- lda AT, _mcount
- jsr AT, (AT), _mcount
- .prologue 1
-#else
- .prologue 0
-#endif
-
- xor a0, a1, t2 # are s1 and s2 co-aligned?
- beq a2, $zerolength
- ldq_u t0, 0(a0) # load asap to give cache time to catch up
- ldq_u t1, 0(a1)
- lda t3, -1
- and t2, 7, t2
- srl t3, 1, t6
- and a0, 7, t4 # find s1 misalignment
- and a1, 7, t5 # find s2 misalignment
- cmovlt a2, t6, a2 # bound neg count to LONG_MAX
- addq a1, a2, a3 # s2+count
- addq a2, t4, a2 # bias count by s1 misalignment
- and a2, 7, t10 # ofs of last byte in s1 last word
- srl a2, 3, a2 # remaining full words in s1 count
- bne t2, $unaligned
-
- /* On entry to this basic block:
- t0 == the first word of s1.
- t1 == the first word of s2.
- t3 == -1. */
-$aligned:
- mskqh t3, a1, t8 # mask off leading garbage
- ornot t1, t8, t1
- ornot t0, t8, t0
- cmpbge zero, t1, t7 # bits set iff null found
- beq a2, $eoc # check end of count
- bne t7, $eos
- beq t10, $ant_loop
-
- /* Aligned compare main loop.
- On entry to this basic block:
- t0 == an s1 word.
- t1 == an s2 word not containing a null. */
-
- .align 4
-$a_loop:
- xor t0, t1, t2 # e0 :
- bne t2, $wordcmp # .. e1 (zdb)
- ldq_u t1, 8(a1) # e0 :
- ldq_u t0, 8(a0) # .. e1 :
-
- subq a2, 1, a2 # e0 :
- addq a1, 8, a1 # .. e1 :
- addq a0, 8, a0 # e0 :
- beq a2, $eoc # .. e1 :
-
- cmpbge zero, t1, t7 # e0 :
- beq t7, $a_loop # .. e1 :
-
- br $eos
-
- /* Alternate aligned compare loop, for when there's no trailing
- bytes on the count. We have to avoid reading too much data. */
- .align 4
-$ant_loop:
- xor t0, t1, t2 # e0 :
- ev6_unop
- ev6_unop
- bne t2, $wordcmp # .. e1 (zdb)
-
- subq a2, 1, a2 # e0 :
- beq a2, $zerolength # .. e1 :
- ldq_u t1, 8(a1) # e0 :
- ldq_u t0, 8(a0) # .. e1 :
-
- addq a1, 8, a1 # e0 :
- addq a0, 8, a0 # .. e1 :
- cmpbge zero, t1, t7 # e0 :
- beq t7, $ant_loop # .. e1 :
-
- br $eos
-
- /* The two strings are not co-aligned. Align s1 and cope. */
- /* On entry to this basic block:
- t0 == the first word of s1.
- t1 == the first word of s2.
- t3 == -1.
- t4 == misalignment of s1.
- t5 == misalignment of s2.
- t10 == misalignment of s1 end. */
- .align 4
-$unaligned:
- /* If s1 misalignment is larger than s2 misalignment, we need
- extra startup checks to avoid SEGV. */
- subq a1, t4, a1 # adjust s2 for s1 misalignment
- cmpult t4, t5, t9
- subq a3, 1, a3 # last byte of s2
- bic a1, 7, t8
- mskqh t3, t5, t7 # mask garbage in s2
- subq a3, t8, a3
- ornot t1, t7, t7
- srl a3, 3, a3 # remaining full words in s2 count
- beq t9, $u_head
-
- /* Failing that, we need to look for both eos and eoc within the
- first word of s2. If we find either, we can continue by
- pretending that the next word of s2 is all zeros. */
- lda t2, 0 # next = zero
- cmpeq a3, 0, t8 # eoc in the first word of s2?
- cmpbge zero, t7, t7 # eos in the first word of s2?
- or t7, t8, t8
- bne t8, $u_head_nl
-
- /* We know just enough now to be able to assemble the first
- full word of s2. We can still find a zero at the end of it.
-
- On entry to this basic block:
- t0 == first word of s1
- t1 == first partial word of s2.
- t3 == -1.
- t10 == ofs of last byte in s1 last word.
- t11 == ofs of last byte in s2 last word. */
-$u_head:
- ldq_u t2, 8(a1) # load second partial s2 word
- subq a3, 1, a3
-$u_head_nl:
- extql t1, a1, t1 # create first s2 word
- mskqh t3, a0, t8
- extqh t2, a1, t4
- ornot t0, t8, t0 # kill s1 garbage
- or t1, t4, t1 # s2 word now complete
- cmpbge zero, t0, t7 # find eos in first s1 word
- ornot t1, t8, t1 # kill s2 garbage
- beq a2, $eoc
- subq a2, 1, a2
- bne t7, $eos
- mskql t3, a1, t8 # mask out s2[1] bits we have seen
- xor t0, t1, t4 # compare aligned words
- or t2, t8, t8
- bne t4, $wordcmp
- cmpbge zero, t8, t7 # eos in high bits of s2[1]?
- cmpeq a3, 0, t8 # eoc in s2[1]?
- or t7, t8, t7
- bne t7, $u_final
-
- /* Unaligned copy main loop. In order to avoid reading too much,
- the loop is structured to detect zeros in aligned words from s2.
- This has, unfortunately, effectively pulled half of a loop
- iteration out into the head and half into the tail, but it does
- prevent nastiness from accumulating in the very thing we want
- to run as fast as possible.
-
- On entry to this basic block:
- t2 == the unshifted low-bits from the next s2 word.
- t10 == ofs of last byte in s1 last word.
- t11 == ofs of last byte in s2 last word. */
- .align 4
-$u_loop:
- extql t2, a1, t3 # e0 :
- ldq_u t2, 16(a1) # .. e1 : load next s2 high bits
- ldq_u t0, 8(a0) # e0 : load next s1 word
- addq a1, 8, a1 # .. e1 :
-
- addq a0, 8, a0 # e0 :
- subq a3, 1, a3 # .. e1 :
- extqh t2, a1, t1 # e0 :
- cmpbge zero, t0, t7 # .. e1 : eos in current s1 word
-
- or t1, t3, t1 # e0 :
- beq a2, $eoc # .. e1 : eoc in current s1 word
- subq a2, 1, a2 # e0 :
- cmpbge zero, t2, t4 # .. e1 : eos in s2[1]
-
- xor t0, t1, t3 # e0 : compare the words
- ev6_unop
- ev6_unop
- bne t7, $eos # .. e1 :
-
- cmpeq a3, 0, t5 # e0 : eoc in s2[1]
- ev6_unop
- ev6_unop
- bne t3, $wordcmp # .. e1 :
-
- or t4, t5, t4 # e0 : eos or eoc in s2[1].
- beq t4, $u_loop # .. e1 (zdb)
-
- /* We've found a zero in the low bits of the last s2 word. Get
- the next s1 word and align them. */
- .align 3
-$u_final:
- ldq_u t0, 8(a0)
- extql t2, a1, t1
- cmpbge zero, t1, t7
- bne a2, $eos
-
- /* We've hit end of count. Zero everything after the count
- and compare whats left. */
- .align 3
-$eoc:
- mskql t0, t10, t0
- mskql t1, t10, t1
- cmpbge zero, t1, t7
-
- /* We've found a zero somewhere in a word we just read.
- On entry to this basic block:
- t0 == s1 word
- t1 == s2 word
- t7 == cmpbge mask containing the zero. */
- .align 3
-$eos:
- negq t7, t6 # create bytemask of valid data
- and t6, t7, t8
- subq t8, 1, t6
- or t6, t8, t7
- zapnot t0, t7, t0 # kill the garbage
- zapnot t1, t7, t1
- xor t0, t1, v0 # ... and compare
- beq v0, $done
-
- /* Here we have two differing co-aligned words in t0 & t1.
- Bytewise compare them and return (t0 > t1 ? 1 : -1). */
- .align 3
-$wordcmp:
- cmpbge t0, t1, t2 # comparison yields bit mask of ge
- cmpbge t1, t0, t3
- xor t2, t3, t0 # bits set iff t0/t1 bytes differ
- negq t0, t1 # clear all but least bit
- and t0, t1, t0
- lda v0, -1
- and t0, t2, t1 # was bit set in t0 > t1?
- cmovne t1, 1, v0
-$done:
- ret
-
- .align 3
-$zerolength:
- clr v0
- ret
-
- END(strncmp)
-libc_hidden_builtin_def (strncmp)