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
| /* SPDX-License-Identifier: GPL-2.0 */
| /*
| * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
| *
| * Finds length of a 0-terminated string. Optimized for the
| * Alpha architecture:
| *
| * - memory accessed as aligned quadwords only
| * - uses bcmpge 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).
| */
| #include <asm/export.h>
| .set noreorder
| .set noat
|
| .align 3
|
| .globl strlen
| .ent strlen
|
| strlen:
| ldq_u $1, 0($16) # load first quadword ($16 may be misaligned)
| lda $2, -1($31)
| insqh $2, $16, $2
| andnot $16, 7, $0
| or $2, $1, $1
| cmpbge $31, $1, $2 # $2 <- bitmask: bit i == 1 <==> i-th byte == 0
| bne $2, found
|
| loop: ldq $1, 8($0)
| addq $0, 8, $0 # addr += 8
| nop # helps dual issue last two insns
| cmpbge $31, $1, $2
| beq $2, loop
|
| found: blbs $2, done # make aligned case fast
| negq $2, $3
| and $2, $3, $2
|
| and $2, 0x0f, $1
| addq $0, 4, $3
| cmoveq $1, $3, $0
|
| and $2, 0x33, $1
| addq $0, 2, $3
| cmoveq $1, $3, $0
|
| and $2, 0x55, $1
| addq $0, 1, $3
| cmoveq $1, $3, $0
|
| done: subq $0, $16, $0
| ret $31, ($26)
|
| .end strlen
| EXPORT_SYMBOL(strlen)
|
|
