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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * arch/alpha/lib/ev67-strlen.S
3 * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
4 *
5 * Finds length of a 0-terminated string. Optimized for the
6 * Alpha architecture:
7 *
8 * - memory accessed as aligned quadwords only
9 * - uses bcmpge to compare 8 bytes in parallel
10 *
11 * Much of the information about 21264 scheduling/coding comes from:
12 * Compiler Writer's Guide for the Alpha 21264
13 * abbreviated as 'CWG' in other comments here
14 * ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
15 * Scheduling notation:
16 * E - either cluster
17 * U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
18 * L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
19 */
20
21 .set noreorder
22 .set noat
23
24 .globl strlen
25 .ent strlen
26 .align 4
27strlen:
28 ldq_u $1, 0($16) # L : load first quadword ($16 may be misaligned)
29 lda $2, -1($31) # E :
30 insqh $2, $16, $2 # U :
31 andnot $16, 7, $0 # E :
32
33 or $2, $1, $1 # E :
34 cmpbge $31, $1, $2 # E : $2 <- bitmask: bit i == 1 <==> i-th byte == 0
35 nop # E :
36 bne $2, $found # U :
37
38$loop: ldq $1, 8($0) # L :
39 addq $0, 8, $0 # E : addr += 8
40 cmpbge $31, $1, $2 # E :
41 beq $2, $loop # U :
42
43$found:
44 cttz $2, $3 # U0 :
45 addq $0, $3, $0 # E :
46 subq $0, $16, $0 # E :
47 ret $31, ($26) # L0 :
48
49 .end strlen