1 /* SPDX-License-Identifier: GPL-2.0 */ 1 /* SPDX-License-Identifier: GPL-2.0 */
2 /* 2 /*
3 * strlen.S (c) 1995 David Mosberger (davidm@c 3 * strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
4 * 4 *
5 * Finds length of a 0-terminated string. Opt 5 * Finds length of a 0-terminated string. Optimized for the
6 * Alpha architecture: 6 * Alpha architecture:
7 * 7 *
8 * - memory accessed as aligned quadwords 8 * - memory accessed as aligned quadwords only
9 * - uses bcmpge to compare 8 bytes in pa 9 * - uses bcmpge to compare 8 bytes in parallel
10 * - does binary search to find 0 byte in 10 * - does binary search to find 0 byte in last
11 * quadword (HAKMEM needed 12 instructi 11 * quadword (HAKMEM needed 12 instructions to
12 * do this instead of the 9 instruction 12 * do this instead of the 9 instructions that
13 * binary search needs). 13 * binary search needs).
14 */ 14 */
15 #include <linux/export.h> 15 #include <linux/export.h>
16 .set noreorder 16 .set noreorder
17 .set noat 17 .set noat
18 18
19 .align 3 19 .align 3
20 20
21 .globl strlen 21 .globl strlen
22 .ent strlen 22 .ent strlen
23 23
24 strlen: 24 strlen:
25 ldq_u $1, 0($16) # load first q 25 ldq_u $1, 0($16) # load first quadword ($16 may be misaligned)
26 lda $2, -1($31) 26 lda $2, -1($31)
27 insqh $2, $16, $2 27 insqh $2, $16, $2
28 andnot $16, 7, $0 28 andnot $16, 7, $0
29 or $2, $1, $1 29 or $2, $1, $1
30 cmpbge $31, $1, $2 # $2 <- bitma 30 cmpbge $31, $1, $2 # $2 <- bitmask: bit i == 1 <==> i-th byte == 0
31 bne $2, found 31 bne $2, found
32 32
33 loop: ldq $1, 8($0) 33 loop: ldq $1, 8($0)
34 addq $0, 8, $0 # addr += 8 34 addq $0, 8, $0 # addr += 8
35 nop # helps dual i 35 nop # helps dual issue last two insns
36 cmpbge $31, $1, $2 36 cmpbge $31, $1, $2
37 beq $2, loop 37 beq $2, loop
38 38
39 found: blbs $2, done # make aligned 39 found: blbs $2, done # make aligned case fast
40 negq $2, $3 40 negq $2, $3
41 and $2, $3, $2 41 and $2, $3, $2
42 42
43 and $2, 0x0f, $1 43 and $2, 0x0f, $1
44 addq $0, 4, $3 44 addq $0, 4, $3
45 cmoveq $1, $3, $0 45 cmoveq $1, $3, $0
46 46
47 and $2, 0x33, $1 47 and $2, 0x33, $1
48 addq $0, 2, $3 48 addq $0, 2, $3
49 cmoveq $1, $3, $0 49 cmoveq $1, $3, $0
50 50
51 and $2, 0x55, $1 51 and $2, 0x55, $1
52 addq $0, 1, $3 52 addq $0, 1, $3
53 cmoveq $1, $3, $0 53 cmoveq $1, $3, $0
54 54
55 done: subq $0, $16, $0 55 done: subq $0, $16, $0
56 ret $31, ($26) 56 ret $31, ($26)
57 57
58 .end strlen 58 .end strlen
59 EXPORT_SYMBOL(strlen) 59 EXPORT_SYMBOL(strlen)
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