blob: fe63353de152d3bf1d5a24b18b704bde21c161f2 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
3 *
4 * Finds length of a 0-terminated string. Optimized for the
5 * Alpha architecture:
6 *
7 * - memory accessed as aligned quadwords only
8 * - uses bcmpge to compare 8 bytes in parallel
9 * - does binary search to find 0 byte in last
10 * quadword (HAKMEM needed 12 instructions to
11 * do this instead of the 9 instructions that
12 * binary search needs).
13 */
14
15 .set noreorder
16 .set noat
17
18 .align 3
19
20 .globl strlen
21 .ent strlen
22
23strlen:
24 ldq_u $1, 0($16) # load first quadword ($16 may be misaligned)
25 lda $2, -1($31)
26 insqh $2, $16, $2
27 andnot $16, 7, $0
28 or $2, $1, $1
29 cmpbge $31, $1, $2 # $2 <- bitmask: bit i == 1 <==> i-th byte == 0
30 bne $2, found
31
32loop: ldq $1, 8($0)
33 addq $0, 8, $0 # addr += 8
34 nop # helps dual issue last two insns
35 cmpbge $31, $1, $2
36 beq $2, loop
37
38found: blbs $2, done # make aligned case fast
39 negq $2, $3
40 and $2, $3, $2
41
42 and $2, 0x0f, $1
43 addq $0, 4, $3
44 cmoveq $1, $3, $0
45
46 and $2, 0x33, $1
47 addq $0, 2, $3
48 cmoveq $1, $3, $0
49
50 and $2, 0x55, $1
51 addq $0, 1, $3
52 cmoveq $1, $3, $0
53
54done: subq $0, $16, $0
55 ret $31, ($26)
56
57 .end strlen