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