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/*
* arch/alpha/lib/ev67-strrchr.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
*/
#include <asm/regdef.h>
.set noreorder
.set noat
.align 4
.ent strrchr
.globl strrchr
strrchr:
.frame sp, 0, ra
.prologue 0
and a1, 0xff, t2 # E : 00000000000000ch
insbl a1, 1, t4 # U : 000000000000ch00
insbl a1, 2, t5 # U : 0000000000ch0000
ldq_u t0, 0(a0) # L : load first quadword Latency=3
mov zero, t6 # E : t6 is last match aligned addr
or t2, t4, a1 # E : 000000000000chch
sll t5, 8, t3 # U : 00000000ch000000
mov zero, t8 # E : t8 is last match byte compare mask
andnot a0, 7, v0 # E : align source addr
or t5, t3, t3 # E : 00000000chch0000
sll a1, 32, t2 # U : 0000chch00000000
sll a1, 48, t4 # U : chch000000000000
or t4, a1, a1 # E : chch00000000chch
or t2, t3, t2 # E : 0000chchchch0000
or a1, t2, a1 # E : chchchchchchchch
lda t5, -1 # E : build garbage mask
cmpbge zero, t0, t1 # E : bits set iff byte == zero
mskqh t5, a0, t4 # E : Complete garbage mask
xor t0, a1, t2 # E : make bytes == c zero
cmpbge zero, t4, t4 # E : bits set iff byte is garbage
cmpbge zero, t2, t3 # E : bits set iff byte == c
andnot t1, t4, t1 # E : clear garbage from null test
andnot t3, t4, t3 # E : clear garbage from char test
bne t1, $eos # U : did we already hit the terminator?
/* Character search main loop */
$loop:
ldq t0, 8(v0) # L : load next quadword
cmovne t3, v0, t6 # E : save previous comparisons match
nop # : Latency=2, extra map slot (keep nop with cmov)
nop
cmovne t3, t3, t8 # E : Latency=2, extra map slot
nop # : keep with cmovne
addq v0, 8, v0 # E :
xor t0, a1, t2 # E :
cmpbge zero, t0, t1 # E : bits set iff byte == zero
cmpbge zero, t2, t3 # E : bits set iff byte == c
beq t1, $loop # U : if we havnt seen a null, loop
nop
/* Mask out character matches after terminator */
$eos:
negq t1, t4 # E : isolate first null byte match
and t1, t4, t4 # E :
subq t4, 1, t5 # E : build a mask of the bytes up to...
or t4, t5, t4 # E : ... and including the null
and t3, t4, t3 # E : mask out char matches after null
cmovne t3, t3, t8 # E : save it, if match found Latency=2, extra map slot
nop # : Keep with cmovne
nop
cmovne t3, v0, t6 # E :
nop # : Keep with cmovne
/* Locate the address of the last matched character */
ctlz t8, t2 # U0 : Latency=3 (0x40 for t8=0)
nop
cmoveq t8, 0x3f, t2 # E : Compensate for case when no match is seen
nop # E : hide the cmov latency (2) behind ctlz latency
lda t5, 0x3f($31) # E :
subq t5, t2, t5 # E : Normalize leading zero count
addq t6, t5, v0 # E : and add to quadword address
ret # L0 : Latency=3
nop
nop
.end strrchr
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