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149 lines
3.4 KiB
149 lines
3.4 KiB
/* Intel SIMD MMX implementation of Viterbi ACS butterflies
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for 64-state (k=7) convolutional code
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Copyright 2004 Phil Karn, KA9Q
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This code may be used under the terms of the GNU Lesser General Public License (LGPL)
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int update_viterbi27_blk_mmx(struct v27 *vp,unsigned char *syms,int nbits) ;
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*/
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# MMX (64-bit SIMD) version
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# requires Pentium-MMX, Pentium-II or better
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# These are offsets into struct v27, defined in viterbi27_mmx.c
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.set DP,128
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.set OLDMETRICS,132
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.set NEWMETRICS,136
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.text
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.global update_viterbi27_blk_mmx,Mettab27_1,Mettab27_2
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.type update_viterbi27_blk_mmx,@function
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.align 16
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update_viterbi27_blk_mmx:
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pushl %ebp
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movl %esp,%ebp
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pushl %esi
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pushl %edi
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pushl %edx
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pushl %ebx
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movl 8(%ebp),%edx # edx = vp
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testl %edx,%edx
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jnz 0f
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movl -1,%eax
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jmp err
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0: movl OLDMETRICS(%edx),%esi # esi -> old metrics
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movl NEWMETRICS(%edx),%edi # edi -> new metrics
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movl DP(%edx),%edx # edx -> decisions
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1: movl 16(%ebp),%eax # eax = nbits
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decl %eax
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jl 2f # passed zero, we're done
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movl %eax,16(%ebp)
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movl 12(%ebp),%ebx # ebx = syms
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movw (%ebx),%ax # ax = second symbol : first symbol
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addl $2,%ebx
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movl %ebx,12(%ebp)
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movb %ah,%bl
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andl $255,%eax
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andl $255,%ebx
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# shift into first array index dimension slot
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shll $5,%eax
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shll $5,%ebx
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# each invocation of this macro will do 8 butterflies in parallel
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.MACRO butterfly GROUP
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# Compute branch metrics
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movq (Mettab27_1+8*\GROUP)(%eax),%mm3
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movq fifteens,%mm0
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paddb (Mettab27_2+8*\GROUP)(%ebx),%mm3
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paddb ones,%mm3 # emulate pavgb - this may not be necessary
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psrlq $1,%mm3
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pand %mm0,%mm3
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movq (8*\GROUP)(%esi),%mm6 # Incoming path metric, high bit = 0
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movq ((8*\GROUP)+32)(%esi),%mm2 # Incoming path metric, high bit = 1
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movq %mm6,%mm1
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movq %mm2,%mm7
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paddb %mm3,%mm6
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paddb %mm3,%mm2
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pxor %mm0,%mm3 # invert branch metric
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paddb %mm3,%mm7 # path metric for inverted symbols
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paddb %mm3,%mm1
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# live registers 1 2 6 7
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# Compare mm6 and mm7; mm1 and mm2
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pxor %mm3,%mm3
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movq %mm6,%mm4
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movq %mm1,%mm5
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psubb %mm7,%mm4 # mm4 = mm6 - mm7
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psubb %mm2,%mm5 # mm5 = mm1 - mm2
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pcmpgtb %mm3,%mm4 # mm4 = first set of decisions (ff = 1 better)
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pcmpgtb %mm3,%mm5 # mm5 = second set of decisions
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# live registers 1 2 4 5 6 7
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# select survivors
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movq %mm4,%mm0
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pand %mm4,%mm7
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movq %mm5,%mm3
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pand %mm5,%mm2
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pandn %mm6,%mm0
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pandn %mm1,%mm3
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por %mm0,%mm7 # mm7 = first set of survivors
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por %mm3,%mm2 # mm2 = second set of survivors
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# live registers 2 4 5 7
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# interleave & store decisions in mm4, mm5
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# interleave & store new branch metrics in mm2, mm7
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movq %mm4,%mm3
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movq %mm7,%mm0
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punpckhbw %mm5,%mm4
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punpcklbw %mm5,%mm3
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punpcklbw %mm2,%mm7 # interleave second 8 new metrics
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punpckhbw %mm2,%mm0 # interleave first 8 new metrics
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movq %mm4,(16*\GROUP+8)(%edx)
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movq %mm3,(16*\GROUP)(%edx)
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movq %mm7,(16*\GROUP)(%edi)
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movq %mm0,(16*\GROUP+8)(%edi)
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.endm
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# invoke macro 4 times for a total of 32 butterflies
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butterfly GROUP=0
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butterfly GROUP=1
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butterfly GROUP=2
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butterfly GROUP=3
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addl $64,%edx # bump decision pointer
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# swap metrics
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movl %esi,%eax
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movl %edi,%esi
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movl %eax,%edi
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jmp 1b
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2: emms
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movl 8(%ebp),%ebx # ebx = vp
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# stash metric pointers
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movl %esi,OLDMETRICS(%ebx)
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movl %edi,NEWMETRICS(%ebx)
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movl %edx,DP(%ebx) # stash incremented value of vp->dp
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xorl %eax,%eax
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err: popl %ebx
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popl %edx
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popl %edi
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popl %esi
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popl %ebp
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ret
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.data
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.align 8
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fifteens:
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.byte 15,15,15,15,15,15,15,15
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.align 8
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ones: .byte 1,1,1,1,1,1,1,1
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