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202 lines
6.0 KiB
202 lines
6.0 KiB
/* K=9 r=1/3 Viterbi decoder for x86 SSE
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* Copyright Aug 2006, Phil Karn, KA9Q
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* May be used under the terms of the GNU Lesser General Public License (LGPL)
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*/
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#include <xmmintrin.h>
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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 <limits.h>
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#include "fec.h"
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typedef union { unsigned long w[8]; unsigned char c[32];} decision_t;
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typedef union { signed short s[256]; __m64 v[64];} metric_t;
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static union branchtab39 { unsigned short s[128]; __m64 v[32];} Branchtab39[3];
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static int Init = 0;
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/* State info for instance of Viterbi decoder */
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struct v39 {
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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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void *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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void *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_viterbi39_sse(void *p,int starting_state){
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struct v39 *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<256;i++)
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vp->metrics1.s[i] = (SHRT_MIN+1000);
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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->s[starting_state & 255] = SHRT_MIN; /* 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_viterbi39_sse(int len){
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struct v39 *vp;
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if(!Init){
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int polys[3] = { V39POLYA, V39POLYB, V39POLYC };
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set_viterbi39_polynomial_sse(polys);
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}
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if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL){
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return NULL;
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}
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if((vp->decisions = malloc((len+8)*sizeof(decision_t))) == NULL){
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free(vp);
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return NULL;
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}
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init_viterbi39_sse(vp,0);
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return vp;
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}
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void set_viterbi39_polynomial_sse(int polys[3]){
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int state;
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for(state=0;state < 128;state++){
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Branchtab39[0].s[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0;
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Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0;
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Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0;
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}
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Init++;
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}
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/* Viterbi chainback */
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int chainback_viterbi39_sse(
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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 v39 *vp = p;
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decision_t *d;
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int path_metric;
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if(p == NULL)
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return -1;
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d = (decision_t *)vp->decisions;
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endstate %= 256;
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path_metric = vp->old_metrics->s[endstate];
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/* The store into data[] only needs to be done every 8 bits.
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* But this avoids a conditional branch, and the writes will
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* combine in the cache anyway
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*/
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d += 8; /* Look past tail */
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while(nbits-- != 0){
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int k;
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/* k = (d[nbits].w[endstate/32] >> (endstate%32)) & 1;*/
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k = (d[nbits].c[endstate/8] >> (endstate%8)) & 1;
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endstate = (k << 7) | (endstate >> 1);
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data[nbits>>3] = endstate;
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}
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return path_metric - SHRT_MIN;
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}
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/* Delete instance of a Viterbi decoder */
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void delete_viterbi39_sse(void *p){
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struct v39 *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_viterbi39_blk_sse(void *p,unsigned char *syms,int nbits){
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struct v39 *vp = p;
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decision_t *d;
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int path_metric = 0;
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if(p == NULL)
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return -1;
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d = (decision_t *)vp->dp;
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while(nbits--){
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__m64 sym0v,sym1v,sym2v;
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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_pi16(syms[0]);
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sym1v = _mm_set1_pi16(syms[1]);
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sym2v = _mm_set1_pi16(syms[2]);
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syms += 3;
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for(i=0;i<32;i++){
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__m64 decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
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/* Form branch metrics
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* Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255,
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* the XOR operations constitute conditional negation.
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* metric and m_metric (-metric) are in the range 0-765
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*/
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m0 = _mm_add_pi16(_mm_xor_si64(Branchtab39[0].v[i],sym0v),_mm_xor_si64(Branchtab39[1].v[i],sym1v));
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metric = _mm_add_pi16(_mm_xor_si64(Branchtab39[2].v[i],sym2v),m0);
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m_metric = _mm_sub_pi16(_mm_set1_pi16(765),metric);
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/* Add branch metrics to path metrics */
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m0 = _mm_adds_pi16(vp->old_metrics->v[i],metric);
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m3 = _mm_adds_pi16(vp->old_metrics->v[32+i],metric);
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m1 = _mm_adds_pi16(vp->old_metrics->v[32+i],m_metric);
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m2 = _mm_adds_pi16(vp->old_metrics->v[i],m_metric);
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/* Compare and select */
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survivor0 = _mm_min_pi16(m0,m1);
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survivor1 = _mm_min_pi16(m2,m3);
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decision0 = _mm_cmpeq_pi16(survivor0,m1);
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decision1 = _mm_cmpeq_pi16(survivor1,m3);
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/* Pack decisions into 8 bits and store */
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d->c[i] = _mm_movemask_pi8(_mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64())));
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/* Store surviving metrics */
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vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1);
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vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1);
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}
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/* See if we need to renormalize
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* Max metric spread for this code with 0-255 branch metrics is 12750
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*/
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if(vp->new_metrics->s[0] >= SHRT_MAX-5000){
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int i,adjust;
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__m64 adjustv;
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union { __m64 v; signed short w[4]; } t;
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/* Find smallest metric and set adjustv to bring it down to SHRT_MIN */
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adjustv = vp->new_metrics->v[0];
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for(i=1;i<64;i++)
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adjustv = _mm_min_pi16(adjustv,vp->new_metrics->v[i]);
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adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,32));
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adjustv = _mm_min_pi16(adjustv,_mm_srli_si64(adjustv,16));
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t.v = adjustv;
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adjust = t.w[0] - SHRT_MIN;
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path_metric += adjust;
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adjustv = _mm_set1_pi16(adjust);
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for(i=0;i<64;i++)
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vp->new_metrics->v[i] = _mm_sub_pi16(vp->new_metrics->v[i],adjustv);
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}
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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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_mm_empty();
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return path_metric;
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}
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