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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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