1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
|
/* 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
|
