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60 lines
1.1 KiB
ArmAsm
60 lines
1.1 KiB
ArmAsm
/*
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* strlen.S (c) 1995 David Mosberger (davidm@cs.arizona.edu)
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*
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* Finds length of a 0-terminated string. Optimized for the
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* Alpha architecture:
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*
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* - memory accessed as aligned quadwords only
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* - uses bcmpge to compare 8 bytes in parallel
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* - does binary search to find 0 byte in last
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* quadword (HAKMEM needed 12 instructions to
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* do this instead of the 9 instructions that
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* binary search needs).
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*/
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.set noreorder
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.set noat
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.align 3
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.globl strlen
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.ent strlen
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strlen:
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.frame $sp, 0, $26, 0
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.prologue 0
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ldq_u $1, 0($16) # load first quadword ($16 may be misaligned)
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lda $2, -1($31)
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insqh $2, $16, $2
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andnot $16, 7, $0
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or $2, $1, $1
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cmpbge $31, $1, $2 # $2 <- bitmask: bit i == 1 <==> i-th byte == 0
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bne $2, found
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loop: ldq $1, 8($0)
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addq $0, 8, $0 # addr += 8
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nop # helps dual issue last two insns
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cmpbge $31, $1, $2
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beq $2, loop
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found: blbs $2, done # make aligned case fast
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negq $2, $3
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and $2, $3, $2
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and $2, 0x0f, $1
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addq $0, 4, $3
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cmoveq $1, $3, $0
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and $2, 0x33, $1
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addq $0, 2, $3
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cmoveq $1, $3, $0
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and $2, 0x55, $1
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addq $0, 1, $3
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cmoveq $1, $3, $0
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done: subq $0, $16, $0
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ret $31, ($26)
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.end strlen
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