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1da177e4 LT |
1 | /* Copyright (C) 1996 Free Software Foundation, Inc. |
2 | This file is part of the GNU C Library. | |
3 | Contributed by David Mosberger (davidm@cs.arizona.edu). | |
4 | ||
5 | The GNU C Library is free software; you can redistribute it and/or | |
6 | modify it under the terms of the GNU Library General Public License as | |
7 | published by the Free Software Foundation; either version 2 of the | |
8 | License, or (at your option) any later version. | |
9 | ||
10 | The GNU C Library is distributed in the hope that it will be useful, | |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
13 | Library General Public License for more details. | |
14 | ||
15 | You should have received a copy of the GNU Library General Public | |
16 | License along with the GNU C Library; see the file COPYING.LIB. If not, | |
17 | write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, | |
18 | Boston, MA 02111-1307, USA. */ | |
19 | ||
20 | /* Finds characters in a memory area. Optimized for the Alpha: | |
21 | ||
22 | - memory accessed as aligned quadwords only | |
23 | - uses cmpbge to compare 8 bytes in parallel | |
24 | - does binary search to find 0 byte in last | |
25 | quadword (HAKMEM needed 12 instructions to | |
26 | do this instead of the 9 instructions that | |
27 | binary search needs). | |
28 | ||
29 | For correctness consider that: | |
30 | ||
31 | - only minimum number of quadwords may be accessed | |
32 | - the third argument is an unsigned long | |
33 | */ | |
34 | ||
35 | .set noreorder | |
36 | .set noat | |
37 | ||
38 | .globl memchr | |
39 | .ent memchr | |
40 | memchr: | |
41 | .frame $30,0,$26,0 | |
42 | .prologue 0 | |
43 | ||
44 | # Hack -- if someone passes in (size_t)-1, hoping to just | |
45 | # search til the end of the address space, we will overflow | |
46 | # below when we find the address of the last byte. Given | |
47 | # that we will never have a 56-bit address space, cropping | |
48 | # the length is the easiest way to avoid trouble. | |
49 | zap $18, 0x80, $5 #-e0 : | |
50 | ||
51 | beq $18, $not_found # .. e1 : | |
52 | ldq_u $1, 0($16) # e1 : load first quadword | |
53 | insbl $17, 1, $2 # .. e0 : $2 = 000000000000ch00 | |
54 | and $17, 0xff, $17 #-e0 : $17 = 00000000000000ch | |
55 | cmpult $18, 9, $4 # .. e1 : | |
56 | or $2, $17, $17 # e0 : $17 = 000000000000chch | |
57 | lda $3, -1($31) # .. e1 : | |
58 | sll $17, 16, $2 #-e0 : $2 = 00000000chch0000 | |
59 | addq $16, $5, $5 # .. e1 : | |
60 | or $2, $17, $17 # e1 : $17 = 00000000chchchch | |
61 | unop # : | |
62 | sll $17, 32, $2 #-e0 : $2 = chchchch00000000 | |
63 | or $2, $17, $17 # e1 : $17 = chchchchchchchch | |
64 | extql $1, $16, $7 # e0 : | |
65 | beq $4, $first_quad # .. e1 : | |
66 | ||
67 | ldq_u $6, -1($5) #-e1 : eight or less bytes to search | |
68 | extqh $6, $16, $6 # .. e0 : | |
69 | mov $16, $0 # e0 : | |
70 | or $7, $6, $1 # .. e1 : $1 = quadword starting at $16 | |
71 | ||
72 | # Deal with the case where at most 8 bytes remain to be searched | |
73 | # in $1. E.g.: | |
74 | # $18 = 6 | |
75 | # $1 = ????c6c5c4c3c2c1 | |
76 | $last_quad: | |
77 | negq $18, $6 #-e0 : | |
78 | xor $17, $1, $1 # .. e1 : | |
79 | srl $3, $6, $6 # e0 : $6 = mask of $18 bits set | |
80 | cmpbge $31, $1, $2 # .. e1 : | |
81 | and $2, $6, $2 #-e0 : | |
82 | beq $2, $not_found # .. e1 : | |
83 | ||
84 | $found_it: | |
85 | # Now, determine which byte matched: | |
86 | negq $2, $3 # e0 : | |
87 | and $2, $3, $2 # e1 : | |
88 | ||
89 | and $2, 0x0f, $1 #-e0 : | |
90 | addq $0, 4, $3 # .. e1 : | |
91 | cmoveq $1, $3, $0 # e0 : | |
92 | ||
93 | addq $0, 2, $3 # .. e1 : | |
94 | and $2, 0x33, $1 #-e0 : | |
95 | cmoveq $1, $3, $0 # .. e1 : | |
96 | ||
97 | and $2, 0x55, $1 # e0 : | |
98 | addq $0, 1, $3 # .. e1 : | |
99 | cmoveq $1, $3, $0 #-e0 : | |
100 | ||
101 | $done: ret # .. e1 : | |
102 | ||
103 | # Deal with the case where $18 > 8 bytes remain to be | |
104 | # searched. $16 may not be aligned. | |
105 | .align 4 | |
106 | $first_quad: | |
107 | andnot $16, 0x7, $0 #-e1 : | |
108 | insqh $3, $16, $2 # .. e0 : $2 = 0000ffffffffffff ($16<0:2> ff) | |
109 | xor $1, $17, $1 # e0 : | |
110 | or $1, $2, $1 # e1 : $1 = ====ffffffffffff | |
111 | cmpbge $31, $1, $2 #-e0 : | |
112 | bne $2, $found_it # .. e1 : | |
113 | ||
114 | # At least one byte left to process. | |
115 | ||
116 | ldq $1, 8($0) # e0 : | |
117 | subq $5, 1, $18 # .. e1 : | |
118 | addq $0, 8, $0 #-e0 : | |
119 | ||
120 | # Make $18 point to last quad to be accessed (the | |
121 | # last quad may or may not be partial). | |
122 | ||
123 | andnot $18, 0x7, $18 # .. e1 : | |
124 | cmpult $0, $18, $2 # e0 : | |
125 | beq $2, $final # .. e1 : | |
126 | ||
127 | # At least two quads remain to be accessed. | |
128 | ||
129 | subq $18, $0, $4 #-e0 : $4 <- nr quads to be processed | |
130 | and $4, 8, $4 # e1 : odd number of quads? | |
131 | bne $4, $odd_quad_count # e1 : | |
132 | ||
133 | # At least three quads remain to be accessed | |
134 | ||
135 | mov $1, $4 # e0 : move prefetched value to correct reg | |
136 | ||
137 | .align 4 | |
138 | $unrolled_loop: | |
139 | ldq $1, 8($0) #-e0 : prefetch $1 | |
140 | xor $17, $4, $2 # .. e1 : | |
141 | cmpbge $31, $2, $2 # e0 : | |
142 | bne $2, $found_it # .. e1 : | |
143 | ||
144 | addq $0, 8, $0 #-e0 : | |
145 | $odd_quad_count: | |
146 | xor $17, $1, $2 # .. e1 : | |
147 | ldq $4, 8($0) # e0 : prefetch $4 | |
148 | cmpbge $31, $2, $2 # .. e1 : | |
149 | addq $0, 8, $6 #-e0 : | |
150 | bne $2, $found_it # .. e1 : | |
151 | ||
152 | cmpult $6, $18, $6 # e0 : | |
153 | addq $0, 8, $0 # .. e1 : | |
154 | bne $6, $unrolled_loop #-e1 : | |
155 | ||
156 | mov $4, $1 # e0 : move prefetched value into $1 | |
157 | $final: subq $5, $0, $18 # .. e1 : $18 <- number of bytes left to do | |
158 | bne $18, $last_quad # e1 : | |
159 | ||
160 | $not_found: | |
161 | mov $31, $0 #-e0 : | |
162 | ret # .. e1 : | |
163 | ||
164 | .end memchr |