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authorMatthias P. Braendli <matthias.braendli@mpb.li>2014-01-02 21:55:13 +0100
committerMatthias P. Braendli <matthias.braendli@mpb.li>2014-01-02 21:55:13 +0100
commita31630e0d5b9880c716d9004ef4154396ba41ebc (patch)
treeaebbd3b132e5f2dd31bc34750ccded2378fc687a /ssebfly27.s
parent9aaac5be9db5e1537badc65242412ef14c5096e3 (diff)
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Extract fec-3.0.1
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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
+
+
+