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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
| .set OLDMETRICS,132
| .set NEWMETRICS,136
| .text
| .global update_viterbi27_blk_sse,Branchtab27_sse
| .type update_viterbi27_blk_sse,@function
| .align 16
|
| update_viterbi27_blk_sse:
| 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 http://mail.gnu.org/pipermail/bug-gnu-utils/2000-August/002341.html
| .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
| .endm
|
| # 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
| .macro PSUBUSBM REG,MEM
| movq \MEM,%mm7
| psubusb \REG,%mm7
| movq %mm7,\MEM
| .endm
|
| 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
|
| ret
|
| .data
|
| .align 16
| thirtyones:
| .byte 31,31,31,31,31,31,31,31
|
|
|
|
