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/*
* 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).
*/
.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
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