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/* Copyright (C) 1996, 2000 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by David Mosberger (davidm@cs.arizona.edu).
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
/* Finds characters in a memory area. Optimized for the Alpha:
- memory accessed as aligned quadwords only
- uses cmpbge to compare 8 bytes in parallel
- does binary search to find 0 byte in last
quadword (HAKMEM needed 12 instructions to
do this instead of the 9 instructions that
binary search needs).
For correctness consider that:
- only minimum number of quadwords may be accessed
- the third argument is an unsigned long
*/
#include <sysdep.h>
.set noreorder
.set noat
ENTRY(__memchr)
#ifdef PROF
ldgp gp, 0(pv)
lda AT, _mcount
jsr AT, (AT), _mcount
.prologue 1
#else
.prologue 0
#endif
# Hack -- if someone passes in (size_t)-1, hoping to just
# search til the end of the address space, we will overflow
# below when we find the address of the last byte. Given
# that we will never have a 56-bit address space, cropping
# the length is the easiest way to avoid trouble.
zap a2, 0x80, t4 #-e0 :
beq a2, $not_found # .. e1 :
ldq_u t0, 0(a0) # e1 : load first quadword
insbl a1, 1, t1 # .. e0 : t1 = 000000000000ch00
and a1, 0xff, a1 #-e0 : a1 = 00000000000000ch
cmpult a2, 9, t3 # .. e1 :
or t1, a1, a1 # e0 : a1 = 000000000000chch
lda t2, -1(zero) # .. e1 :
sll a1, 16, t1 #-e0 : t1 = 00000000chch0000
addq a0, t4, t4 # .. e1 :
or t1, a1, a1 # e1 : a1 = 00000000chchchch
unop # :
sll a1, 32, t1 #-e0 : t1 = chchchch00000000
or t1, a1, a1 # e1 : a1 = chchchchchchchch
extql t0, a0, t6 # e0 :
beq t3, $first_quad # .. e1 :
ldq_u t5, -1(t4) #-e1 : eight or less bytes to search
extqh t5, a0, t5 # .. e0 :
mov a0, v0 # e0 :
or t6, t5, t0 # .. e1 : t0 = quadword starting at a0
# Deal with the case where at most 8 bytes remain to be searched
# in t0. E.g.:
# a2 = 6
# t0 = ????c6c5c4c3c2c1
$last_quad:
negq a2, t5 #-e0 :
xor a1, t0, t0 # .. e1 :
srl t2, t5, t5 # e0 : t5 = mask of a2 bits set
cmpbge zero, t0, t1 # .. e1 :
and t1, t5, t1 #-e0 :
beq t1, $not_found # .. e1 :
$found_it:
# Now, determine which byte matched:
negq t1, t2 # e0 :
and t1, t2, t1 # e1 :
and t1, 0x0f, t0 #-e0 :
addq v0, 4, t2 # .. e1 :
cmoveq t0, t2, v0 # e0 :
addq v0, 2, t2 # .. e1 :
and t1, 0x33, t0 #-e0 :
cmoveq t0, t2, v0 # .. e1 :
and t1, 0x55, t0 # e0 :
addq v0, 1, t2 # .. e1 :
cmoveq t0, t2, v0 #-e0 :
$done: ret # .. e1 :
# Deal with the case where a2 > 8 bytes remain to be
# searched. a0 may not be aligned.
.align 4
$first_quad:
andnot a0, 0x7, v0 #-e1 :
insqh t2, a0, t1 # .. e0 : t1 = 0000ffffffffffff (a0<0:2> ff)
xor t0, a1, t0 # e0 :
or t0, t1, t0 # e1 : t0 = ====ffffffffffff
cmpbge zero, t0, t1 #-e0 :
bne t1, $found_it # .. e1 :
# At least one byte left to process.
ldq t0, 8(v0) # e0 :
subq t4, 1, a2 # .. e1 :
addq v0, 8, v0 #-e0 :
# Make a2 point to last quad to be accessed (the
# last quad may or may not be partial).
andnot a2, 0x7, a2 # .. e1 :
cmpult v0, a2, t1 # e0 :
beq t1, $final # .. e1 :
# At least two quads remain to be accessed.
subq a2, v0, t3 #-e0 : t3 <- nr quads to be processed
and t3, 8, t3 # e1 : odd number of quads?
bne t3, $odd_quad_count # e1 :
# At least three quads remain to be accessed
mov t0, t3 # e0 : move prefetched value to correct reg
.align 4
$unrolled_loop:
ldq t0, 8(v0) #-e0 : prefetch t0
xor a1, t3, t1 # .. e1 :
cmpbge zero, t1, t1 # e0 :
bne t1, $found_it # .. e1 :
addq v0, 8, v0 #-e0 :
$odd_quad_count:
xor a1, t0, t1 # .. e1 :
ldq t3, 8(v0) # e0 : prefetch t3
cmpbge zero, t1, t1 # .. e1 :
addq v0, 8, t5 #-e0 :
bne t1, $found_it # .. e1 :
cmpult t5, a2, t5 # e0 :
addq v0, 8, v0 # .. e1 :
bne t5, $unrolled_loop #-e1 :
mov t3, t0 # e0 : move prefetched value into t0
$final: subq t4, v0, a2 # .. e1 : a2 <- number of bytes left to do
bne a2, $last_quad # e1 :
$not_found:
mov zero, v0 #-e0 :
ret # .. e1 :
END(__memchr)
weak_alias (__memchr, memchr)
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