ev67-strlen.S
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/*
* arch/alpha/lib/ev67-strlen.S
* 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
*
* 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
*
* Much of the information about 21264 scheduling/coding comes from:
* Compiler Writer's Guide for the Alpha 21264
* abbreviated as 'CWG' in other comments here
* ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
* Scheduling notation:
* E - either cluster
* U - upper subcluster; U0 - subcluster U0; U1 - subcluster U1
* L - lower subcluster; L0 - subcluster L0; L1 - subcluster L1
*/
.set noreorder
.set noat
.globl strlen
.ent strlen
.align 4
strlen:
ldq_u $1, 0($16) # L : load first quadword ($16 may be misaligned)
lda $2, -1($31) # E :
insqh $2, $16, $2 # U :
andnot $16, 7, $0 # E :
or $2, $1, $1 # E :
cmpbge $31, $1, $2 # E : $2 <- bitmask: bit i == 1 <==> i-th byte == 0
nop # E :
bne $2, $found # U :
$loop: ldq $1, 8($0) # L :
addq $0, 8, $0 # E : addr += 8
cmpbge $31, $1, $2 # E :
beq $2, $loop # U :
$found:
cttz $2, $3 # U0 :
addq $0, $3, $0 # E :
subq $0, $16, $0 # E :
ret $31, ($26) # L0 :
.end strlen