/* Copyright (C) 1996-2016 Free Software Foundation, Inc.
Contributed by Richard Henderson (rth@tamu.edu)
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
. */
/* Bytewise compare two null-terminated strings of length no longer than N. */
#include
.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)