/* 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