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// K=7 r=1/2 Viterbi decoder for SSE2
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// Feb 2004, Phil Karn, KA9Q
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// Updated April 2014
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#include <stdio.h>
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#include <stdlib.h>
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#include <memory.h>
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#include <xmmintrin.h>
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#include <stdint.h>
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#include "fec.h"
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static inline int parity(int x){
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return __builtin_parity(x);
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}
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int encode_27(
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unsigned char *symbols, // Output buffer, 2*8*nbytes
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const unsigned char *data, // Input buffer, nbytes
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unsigned int nbytes) // Number of bytes in data
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{
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unsigned int encstate;
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int i;
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encstate = 0;
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while(nbytes-- != 0){
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encstate |= *data++;
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for(i=0;i<8;i++){ // Transmit 8 bits, MSB first
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encstate <<= 1;
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*symbols++ = parity(encstate & (V27POLYB << 8));
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*symbols++ = !parity(encstate & (V27POLYA << 8));
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}
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}
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if((encstate & (63 << 8)) != 0)
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return -1; // Warn if frame wasn't tailed to 0
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return 0;
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}
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typedef union { uint8_t c[64]; __m128i v[4]; } metric_t;
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typedef union { uint32_t w[2]; uint8_t c[8]; uint16_t s[4]; __m64 v[1];} decision_t;
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union branchtab27 { uint8_t c[32]; __m128i v[2];} Branchtab27_sse2[2];
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// State info for instance of Viterbi decoder
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// Don't change this without also changing references in sse2bfly27.s!
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struct v27 {
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metric_t metrics1; // path metric buffer 1
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metric_t metrics2; // path metric buffer 2
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decision_t *dp; // Pointer to current decision
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metric_t *old_metrics,*new_metrics; // Pointers to path metrics, swapped on every bit
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decision_t *decisions; // Beginning of decisions for block
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};
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// Initialize Viterbi decoder for start of new frame
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int init_viterbi27(void *p,int starting_state){
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struct v27 *vp = p;
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int i;
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if(p == NULL)
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return -1;
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for(i=0;i<64;i++)
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vp->metrics1.c[i] = 63;
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vp->old_metrics = &vp->metrics1;
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vp->new_metrics = &vp->metrics2;
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vp->dp = vp->decisions;
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vp->old_metrics->c[starting_state & 63] = 0; // Bias known start state
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return 0;
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}
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// Create a new instance of a Viterbi decoder
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void *create_viterbi27(int len){
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void *p;
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struct v27 *vp;
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int state;
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for(state=0;state < 32;state++){
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Branchtab27_sse2[0].c[state] = parity((2*state) & V27POLYB) ? 255 : 0;
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Branchtab27_sse2[1].c[state] = !parity((2*state) & V27POLYA) ? 255 : 0;
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}
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// Ordinary malloc() only returns 8-byte alignment, we need 16
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if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v27)))
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return NULL;
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vp = (struct v27 *)p;
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if((p = malloc(len*sizeof(decision_t))) == NULL){
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free(vp);
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return NULL;
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}
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vp->decisions = (decision_t *)p;
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init_viterbi27(vp,0);
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return vp;
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}
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// Viterbi chainback
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int chainback_viterbi27(
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void *p,
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unsigned char *data, // Decoded output data
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unsigned int nbits, // Number of data bits
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unsigned int endstate){ // Terminal encoder state
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struct v27 *vp = p;
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decision_t *d;
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unsigned char dbyte = 0;
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if(p == NULL)
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return -1;
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d = vp->decisions;
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endstate &= 63;
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while(nbits-- != 0){
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int bit;
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// Accumulate decoded data bits as they fall off the right end of endstate
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dbyte = ((endstate & 1) << 7) | (dbyte >> 1);
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if((nbits % 8) == 0)
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data[nbits/8] = dbyte;
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// Extract decision and push onto left (tail) end of encoder
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bit = (d[nbits].w[endstate/32] >> (endstate%32)) & 1;
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endstate = (bit << 5) | (endstate >> 1);
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}
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return 0;
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}
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// Delete instance of a Viterbi decoder
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void delete_viterbi27(void *p){
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struct v27 *vp = p;
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if(vp != NULL){
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free(vp->decisions);
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free(vp);
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}
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}
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int update_viterbi27_blk(void *p,unsigned char *syms,int nbits){
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struct v27 *vp = p;
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decision_t *d;
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if(p == NULL)
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return 0;
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d = (decision_t *)vp->dp;
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while(nbits--){
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__m128i sym0v,sym1v;
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void *tmp;
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int i;
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// Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc
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sym0v = _mm_set1_epi8(syms[0]);
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sym1v = _mm_set1_epi8(syms[1]);
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syms += 2;
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#if 0
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for(i=0;i<2;i++){
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__m128i decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
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/* Form branch metrics */
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metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[i],sym0v),_mm_xor_si128(Branchtab27_sse2[1].v[i],sym1v));
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// There's no packed bytes right shift in SSE2, so we use the word version and mask
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// (I'm *really* starting to like Altivec...)
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metric = _mm_srli_epi16(metric,3);
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metric = _mm_and_si128(metric,_mm_set1_epi8(31));
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m_metric = _mm_sub_epi8(_mm_set1_epi8(31),metric);
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// Add branch metrics to path metrics
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m0 = _mm_add_epi8(vp->old_metrics->v[i],metric);
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m3 = _mm_add_epi8(vp->old_metrics->v[2+i],metric);
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m1 = _mm_add_epi8(vp->old_metrics->v[2+i],m_metric);
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m2 = _mm_add_epi8(vp->old_metrics->v[i],m_metric);
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// Compare and select, using modulo arithmetic
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decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0,m1),_mm_setzero_si128());
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decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2,m3),_mm_setzero_si128());
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survivor0 = _mm_or_si128(_mm_and_si128(decision0,m1),_mm_andnot_si128(decision0,m0));
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survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_mm_andnot_si128(decision1,m2));
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// Pack each set of decisions into 16 bits
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d->s[2*i] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0,decision1));
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d->s[2*i+1] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0,decision1));
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// Store surviving metrics
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vp->new_metrics->v[2*i] = _mm_unpacklo_epi8(survivor0,survivor1);
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vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi8(survivor0,survivor1);
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}
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#else
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{
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// Unwound version
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__m128i decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1,survivor2,survivor3;
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// First
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// Form branch metrics
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metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[0],sym0v),_mm_xor_si128(Branchtab27_sse2[1].v[0],sym1v));
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// There's no packed bytes right shift in SSE2, so we use the word version and mask
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// (I'm *really* starting to like Altivec...)
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metric = _mm_srli_epi16(metric,3);
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metric = _mm_and_si128(metric,_mm_set1_epi8(31));
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m_metric = _mm_sub_epi8(_mm_set1_epi8(31),metric);
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// Add branch metrics to path metrics
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m0 = _mm_add_epi8(vp->old_metrics->v[0],metric);
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m3 = _mm_add_epi8(vp->old_metrics->v[2],metric);
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m1 = _mm_add_epi8(vp->old_metrics->v[2],m_metric);
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m2 = _mm_add_epi8(vp->old_metrics->v[0],m_metric);
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// Compare and select, using modulo arithmetic
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decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0,m1),_mm_setzero_si128());
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decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2,m3),_mm_setzero_si128());
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survivor0 = _mm_or_si128(_mm_and_si128(decision0,m1),_mm_andnot_si128(decision0,m0));
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survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_mm_andnot_si128(decision1,m2));
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// Pack each set of decisions into 16 bits
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d->s[0] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0,decision1));
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d->s[1] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0,decision1));
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// Store surviving metrics
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vp->new_metrics->v[0] = _mm_unpacklo_epi8(survivor0,survivor1);
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vp->new_metrics->v[1] = _mm_unpackhi_epi8(survivor0,survivor1);
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// Second
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// Form branch metrics
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metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[1],sym0v),_mm_xor_si128(Branchtab27_sse2[1].v[1],sym1v));
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// There's no packed bytes right shift in SSE2, so we use the word version and mask
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// (I'm *really* starting to like Altivec...)
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metric = _mm_srli_epi16(metric,3);
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metric = _mm_and_si128(metric,_mm_set1_epi8(31));
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m_metric = _mm_sub_epi8(_mm_set1_epi8(31),metric);
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// Add branch metrics to path metrics
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m0 = _mm_add_epi8(vp->old_metrics->v[1],metric);
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m3 = _mm_add_epi8(vp->old_metrics->v[3],metric);
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m1 = _mm_add_epi8(vp->old_metrics->v[3],m_metric);
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m2 = _mm_add_epi8(vp->old_metrics->v[1],m_metric);
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// Compare and select, using modulo arithmetic
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decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0,m1),_mm_setzero_si128());
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decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2,m3),_mm_setzero_si128());
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survivor0 = _mm_or_si128(_mm_and_si128(decision0,m1),_mm_andnot_si128(decision0,m0));
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survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_mm_andnot_si128(decision1,m2));
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// Pack each set of decisions into 16 bits
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d->s[2] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0,decision1));
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d->s[3] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0,decision1));
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// Store surviving metrics
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vp->new_metrics->v[2] = _mm_unpacklo_epi8(survivor0,survivor1);
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vp->new_metrics->v[3] = _mm_unpackhi_epi8(survivor0,survivor1);
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}
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#endif
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d++;
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// Swap pointers to old and new metrics
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tmp = vp->old_metrics;
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vp->old_metrics = vp->new_metrics;
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vp->new_metrics = tmp;
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}
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vp->dp = d;
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return 0;
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}
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