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