/* Copyright (C) 1996 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
*/
.set noreorder
.set noat
.globl memchr
.ent memchr
memchr:
.frame $30,0,$26,0
.prologue 0
# 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 $18, 0x80, $5 #-e0 :
beq $18, $not_found # .. e1 :
ldq_u $1, 0($16) # e1 : load first quadword
insbl $17, 1, $2 # .. e0 : $2 = 000000000000ch00
and $17, 0xff, $17 #-e0 : $17 = 00000000000000ch
cmpult $18, 9, $4 # .. e1 :
or $2, $17, $17 # e0 : $17 = 000000000000chch
lda $3, -1($31) # .. e1 :
sll $17, 16, $2 #-e0 : $2 = 00000000chch0000
addq $16, $5, $5 # .. e1 :
or $2, $17, $17 # e1 : $17 = 00000000chchchch
unop # :
sll $17, 32, $2 #-e0 : $2 = chchchch00000000
or $2, $17, $17 # e1 : $17 = chchchchchchchch
extql $1, $16, $7 # e0 :
beq $4, $first_quad # .. e1 :
ldq_u $6, -1($5) #-e1 : eight or less bytes to search
extqh $6, $16, $6 # .. e0 :
mov $16, $0 # e0 :
or $7, $6, $1 # .. e1 : $1 = quadword starting at $16
# Deal with the case where at most 8 bytes remain to be searched
# in $1. E.g.:
# $18 = 6
# $1 = ????c6c5c4c3c2c1
$last_quad:
negq $18, $6 #-e0 :
xor $17, $1, $1 # .. e1 :
srl $3, $6, $6 # e0 : $6 = mask of $18 bits set
cmpbge $31, $1, $2 # .. e1 :
and $2, $6, $2 #-e0 :
beq $2, $not_found # .. e1 :
$found_it:
# Now, determine which byte matched:
negq $2, $3 # e0 :
and $2, $3, $2 # e1 :
and $2, 0x0f, $1 #-e0 :
addq $0, 4, $3 # .. e1 :
cmoveq $1, $3, $0 # e0 :
addq $0, 2, $3 # .. e1 :
and $2, 0x33, $1 #-e0 :
cmoveq $1, $3, $0 # .. e1 :
and $2, 0x55, $1 # e0 :
addq $0, 1, $3 # .. e1 :
cmoveq $1, $3, $0 #-e0 :
$done: ret # .. e1 :
# Deal with the case where $18 > 8 bytes remain to be
# searched. $16 may not be aligned.
.align 4
$first_quad:
andnot $16, 0x7, $0 #-e1 :
insqh $3, $16, $2 # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff)
xor $1, $17, $1 # e0 :
or $1, $2, $1 # e1 : $1 = ====ffffffffffff
cmpbge $31, $1, $2 #-e0 :
bne $2, $found_it # .. e1 :
# At least one byte left to process.
ldq $1, 8($0) # e0 :
subq $5, 1, $18 # .. e1 :
addq $0, 8, $0 #-e0 :
# Make $18 point to last quad to be accessed (the
# last quad may or may not be partial).
andnot $18, 0x7, $18 # .. e1 :
cmpult $0, $18, $2 # e0 :
beq $2, $final # .. e1 :
# At least two quads remain to be accessed.
subq $18, $0, $4 #-e0 : $4 <- nr quads to be processed
and $4, 8, $4 # e1 : odd number of quads?
bne $4, $odd_quad_count # e1 :
# At least three quads remain to be accessed
mov $1, $4 # e0 : move prefetched value to correct reg
.align 4
$unrolled_loop:
ldq $1, 8($0) #-e0 : prefetch $1
xor $17, $4, $2 # .. e1 :
cmpbge $31, $2, $2 # e0 :
bne $2, $found_it # .. e1 :
addq $0, 8, $0 #-e0 :
$odd_quad_count:
xor $17, $1, $2 # .. e1 :
ldq $4, 8($0) # e0 : prefetch $4
cmpbge $31, $2, $2 # .. e1 :
addq $0, 8, $6 #-e0 :
bne $2, $found_it # .. e1 :
cmpult $6, $18, $6 # e0 :
addq $0, 8, $0 # .. e1 :
bne $6, $unrolled_loop #-e1 :
mov $4, $1 # e0 : move prefetched value into $1
$final: subq $5, $0, $18 # .. e1 : $18 <- number of bytes left to do
bne $18, $last_quad # e1 :
$not_found:
mov $31, $0 #-e0 :
ret # .. e1 :
.end memchr
