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/* Intel SIMD (SSE) implementation of Viterbi ACS butterflies
for 64-state (k=7) convolutional code
Copyright 2001 Phil Karn, KA9Q
This code may be used under the terms of the GNU Lesser General Public License (LGPL)
int update_viterbi27_blk_sse(struct v27 *vp,unsigned char syms[],int nbits) ;
# SSE (64-bit integer SIMD) version
# Requires Pentium III or better
# These are offsets into struct v27, defined in viterbi27.h
.set DP,128
.global update_viterbi27_blk_sse,Branchtab27_sse
.type update_viterbi27_blk_sse,@function
.align 16
pushl %ebp
movl %esp,%ebp
pushl %esi
pushl %edi
pushl %edx
pushl %ebx
movl 8(%ebp),%edx # edx = vp
testl %edx,%edx
jnz 0f
movl -1,%eax
jmp err
0: movl OLDMETRICS(%edx),%esi # esi -> old metrics
movl NEWMETRICS(%edx),%edi # edi -> new metrics
movl DP(%edx),%edx # edx -> decisions
1: movl 16(%ebp),%eax # eax = nbits
decl %eax
jl 2f # passed zero, we're done
movl %eax,16(%ebp)
xorl %eax,%eax
movl 12(%ebp),%ebx # %ebx = syms
movb (%ebx),%al
movd %eax,%mm6 # mm6[0] = first symbol
movb 1(%ebx),%al
movd %eax,%mm5 # mm5[0] = second symbol
addl $2,%ebx
movl %ebx,12(%ebp)
punpcklbw %mm6,%mm6 # mm6[1] = mm6[0]
punpcklbw %mm5,%mm5
movq thirtyones,%mm7
pshufw $0,%mm6,%mm6 # copy low word to upper 3
pshufw $0,%mm5,%mm5
# mm6 now contains first symbol in each byte, mm5 the second
# each invocation of this macro does 8 butterflies in parallel
.MACRO butterfly GROUP
# compute branch metrics
movq Branchtab27_sse+(8*\GROUP),%mm4
movq Branchtab27_sse+32+(8*\GROUP),%mm3
pxor %mm6,%mm4
pxor %mm5,%mm3
pavgb %mm3,%mm4 # mm4 contains branch metrics
psrlw $3,%mm4
pand %mm7,%mm4
movq (8*\GROUP)(%esi),%mm0 # Incoming path metric, high bit = 0
movq ((8*\GROUP)+32)(%esi),%mm3 # Incoming path metric, high bit = 1
movq %mm0,%mm2
movq %mm3,%mm1
paddusb %mm4,%mm0
paddusb %mm4,%mm3
# invert branch metrics. This works only because they're 5 bits
pxor %mm7,%mm4
paddusb %mm4,%mm1
paddusb %mm4,%mm2
# Find survivors, leave in mm0,2
pminub %mm1,%mm0
pminub %mm3,%mm2
# get decisions, leave in mm1,3
pcmpeqb %mm0,%mm1
pcmpeqb %mm2,%mm3
# interleave and store new branch metrics in mm0,2
movq %mm0,%mm4
punpckhbw %mm2,%mm0 # interleave second 8 new metrics
punpcklbw %mm2,%mm4 # interleave first 8 new metrics
movq %mm0,(16*\GROUP+8)(%edi)
movq %mm4,(16*\GROUP)(%edi)
# interleave decisions, accumulate into %ebx
movq %mm1,%mm4
punpckhbw %mm3,%mm1
punpcklbw %mm3,%mm4
# Due to an error in the Intel instruction set ref (the register
# fields are swapped), gas assembles pmovmskb incorrectly
# See
.byte 0x0f,0xd7,0xc1 # pmovmskb %mm1,%eax
shll $((16*\GROUP+8)&31),%eax
orl %eax,%ebx
.byte 0x0f,0xd7,0xc4 # pmovmskb %mm4,%eax
shll $((16*\GROUP)&31),%eax
orl %eax,%ebx
# invoke macro 4 times for a total of 32 butterflies
xorl %ebx,%ebx # clear decisions
butterfly GROUP=0
butterfly GROUP=1
movl %ebx,(%edx) # stash first 32 decisions
xorl %ebx,%ebx
butterfly GROUP=2
butterfly GROUP=3
movl %ebx,4(%edx) # stash second 32 decisions
addl $8,%edx # bump decision pointer
# see if we have to normalize
movl (%edi),%eax # extract first output metric
andl $255,%eax
cmpl $150,%eax # is it greater than 150?
movl $0,%eax
jle done # No, no need to normalize
# Normalize by finding smallest metric and subtracting it
# from all metrics
movq (%edi),%mm0
pminub 8(%edi),%mm0
pminub 16(%edi),%mm0
pminub 24(%edi),%mm0
pminub 32(%edi),%mm0
pminub 40(%edi),%mm0
pminub 48(%edi),%mm0
pminub 56(%edi),%mm0
# mm0 contains 8 smallest metrics
# crunch down to single lowest metric
movq %mm0,%mm1
psrlq $32,%mm0
pminub %mm1,%mm0
movq %mm0,%mm1
psrlq $16,%mm0
pminub %mm1,%mm0
movq %mm0,%mm1
psrlq $8,%mm0
pminub %mm1,%mm0
punpcklbw %mm0,%mm0 # expand to all 8 bytes
pshufw $0,%mm0,%mm0
# mm0 now contains lowest metric in all 8 bytes
# subtract it from every output metric
# Trashes %mm7
movq \MEM,%mm7
psubusb \REG,%mm7
movq %mm7,\MEM
PSUBUSBM %mm0,(%edi)
PSUBUSBM %mm0,8(%edi)
PSUBUSBM %mm0,16(%edi)
PSUBUSBM %mm0,24(%edi)
PSUBUSBM %mm0,32(%edi)
PSUBUSBM %mm0,40(%edi)
PSUBUSBM %mm0,48(%edi)
PSUBUSBM %mm0,56(%edi)
movd %mm0,%eax
and $0xff,%eax
done: # swap metrics
movl %esi,%eax
movl %edi,%esi
movl %eax,%edi
jmp 1b
2: emms
movl 8(%ebp),%ebx # ebx = vp
# stash metric pointers
movl %esi,OLDMETRICS(%ebx)
movl %edi,NEWMETRICS(%ebx)
movl %edx,DP(%ebx) # stash incremented value of vp->dp
xorl %eax,%eax
err: popl %ebx
popl %edx
popl %edi
popl %esi
popl %ebp
.align 16
.byte 31,31,31,31,31,31,31,31