90 строки
2.8 KiB
ArmAsm
90 строки
2.8 KiB
ArmAsm
/*
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* arch/alpha/lib/ev67-strchr.S
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* 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
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*
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* Return the address of a given character within a null-terminated
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* string, or null if it is not found.
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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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* Try not to change the actual algorithm if possible for consistency.
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*/
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#include <asm/export.h>
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#include <asm/regdef.h>
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.set noreorder
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.set noat
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.align 4
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.globl strchr
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.ent strchr
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strchr:
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.frame sp, 0, ra
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.prologue 0
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ldq_u t0, 0(a0) # L : load first quadword Latency=3
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and a1, 0xff, t3 # E : 00000000000000ch
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insbl a1, 1, t5 # U : 000000000000ch00
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insbl a1, 7, a2 # U : ch00000000000000
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insbl t3, 6, a3 # U : 00ch000000000000
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or t5, t3, a1 # E : 000000000000chch
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andnot a0, 7, v0 # E : align our loop pointer
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lda t4, -1 # E : build garbage mask
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mskqh t4, a0, t4 # U : only want relevant part of first quad
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or a2, a3, a2 # E : chch000000000000
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inswl a1, 2, t5 # E : 00000000chch0000
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inswl a1, 4, a3 # E : 0000chch00000000
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or a1, a2, a1 # E : chch00000000chch
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or a3, t5, t5 # E : 0000chchchch0000
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cmpbge zero, t0, t2 # E : bits set iff byte == zero
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cmpbge zero, t4, t4 # E : bits set iff byte is garbage
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/* This quad is _very_ serialized. Lots of stalling happens */
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or t5, a1, a1 # E : chchchchchchchch
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xor t0, a1, t1 # E : make bytes == c zero
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cmpbge zero, t1, t3 # E : bits set iff byte == c
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or t2, t3, t0 # E : bits set iff char match or zero match
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andnot t0, t4, t0 # E : clear garbage bits
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cttz t0, a2 # U0 : speculative (in case we get a match)
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nop # E :
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bne t0, $found # U :
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/*
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* Yuk. This loop is going to stall like crazy waiting for the
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* data to be loaded. Not much can be done about it unless it's
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* unrolled multiple times - is that safe to do in kernel space?
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* Or would exception handling recovery code do the trick here?
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*/
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$loop: ldq t0, 8(v0) # L : Latency=3
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addq v0, 8, v0 # E :
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xor t0, a1, t1 # E :
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cmpbge zero, t0, t2 # E : bits set iff byte == 0
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cmpbge zero, t1, t3 # E : bits set iff byte == c
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or t2, t3, t0 # E :
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cttz t3, a2 # U0 : speculative (in case we get a match)
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beq t0, $loop # U :
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$found: negq t0, t1 # E : clear all but least set bit
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and t0, t1, t0 # E :
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and t0, t3, t1 # E : bit set iff byte was the char
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addq v0, a2, v0 # E : Add in the bit number from above
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cmoveq t1, $31, v0 # E : Two mapping slots, latency = 2
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nop
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nop
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ret # L0 :
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.end strchr
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EXPORT_SYMBOL(strchr)
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