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/* K=9 r=1/2 Viterbi decoder for PowerPC G4/G5 Altivec
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* Copyright Feb 2004, 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 <stdio.h>
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#include <stdlib.h>
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#include <memory.h>
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#include <sys/sysctl.h>
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#include "fec.h"
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typedef union { unsigned char c[256]; vector bool char v[16]; } decision_t;
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typedef union { unsigned char c[256]; vector unsigned char v[16]; } metric_t;
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static union branchtab29 { unsigned char c[128]; vector unsigned char v[8]; } Branchtab29[2];
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static int Init = 0;
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/* State info for instance of Viterbi decoder */
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struct v29 {
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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_viterbi29_av(void *p,int starting_state){
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struct v29 *vp = p;
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int i;
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for(i=0;i<16;i++)
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vp->metrics1.v[i] = (vector unsigned char)(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 & 255] = 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_viterbi29_av(int len){
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struct v29 *vp;
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int state;
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if(!Init){
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/* Initialize branch tables */
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for(state=0;state < 128;state++){
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Branchtab29[0].c[state] = parity((2*state) & V29POLYA) ? 255:0;
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Branchtab29[1].c[state] = parity((2*state) & V29POLYB) ? 255:0;
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}
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Init++;
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}
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vp = (struct v29 *)malloc(sizeof(struct v29));
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vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t));
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init_viterbi29_av(vp,0);
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return vp;
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}
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/* Viterbi chainback */
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int chainback_viterbi29_av(
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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 v29 *vp = p;
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decision_t *d = (decision_t *)vp->decisions;
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/* Make room beyond the end of the encoder register so we can
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* accumulate a full byte of decoded data
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*/
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endstate %= 256;
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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].c[endstate] & 1;
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data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
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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_viterbi29_av(void *p){
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struct v29 *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_viterbi29_blk_av(void *p,unsigned char *syms,int nbits){
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struct v29 *vp = p;
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decision_t *d = (decision_t *)vp->dp;
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int i;
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while(nbits--){
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vector unsigned char sym1v,sym2v;
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void *tmp;
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/* All this seems necessary just to load a byte into all elements of a vector! */
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sym1v = vec_perm(vec_ld(0,syms),vec_ld(1,syms),vec_lvsl(0,syms)); /* sym1v.0 = syms[0]; sym1v.1 = syms[1] */
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sym2v = vec_splat(sym1v,1); /* Splat syms[1] across sym2v */
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sym1v = vec_splat(sym1v,0); /* Splat syms[0] across sym1v */
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syms += 2;
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for(i=0;i<8;i+=2){
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vector bool char decision0,decision1;
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vector unsigned char metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
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/* Form branch metrics */
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metric = vec_avg(vec_xor(Branchtab29[0].v[i],sym1v),vec_xor(Branchtab29[1].v[i],sym2v));
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metric = vec_sr(metric,(vector unsigned char)(3));
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m_metric = (vector unsigned char)(31) - metric;
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/* Add branch metrics to path metrics */
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m0 = vec_adds(vp->old_metrics->v[i],metric);
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m3 = vec_adds(vp->old_metrics->v[8+i],metric);
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m1 = vec_adds(vp->old_metrics->v[8+i],m_metric);
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m2 = vec_adds(vp->old_metrics->v[i],m_metric);
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/* Compare and select first set */
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decision0 = vec_cmpgt(m0,m1);
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decision1 = vec_cmpgt(m2,m3);
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survivor0 = vec_min(m0,m1);
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survivor1 = vec_min(m2,m3);
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/* Interleave and store decisions and survivors */
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d->v[2*i] = vec_mergeh(decision0,decision1);
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d->v[2*i+1] = vec_mergel(decision0,decision1);
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vp->new_metrics->v[2*i] = vec_mergeh(survivor0,survivor1);
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vp->new_metrics->v[2*i+1] = vec_mergel(survivor0,survivor1);
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/* Form branch metrics */
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metric = vec_avg(vec_xor(Branchtab29[0].v[i+1],sym1v),vec_xor(Branchtab29[1].v[i+1],sym2v));
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metric = vec_sr(metric,(vector unsigned char)(3));
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m_metric = (vector unsigned char)(31) - metric;
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/* Add branch metrics to path metrics */
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m0 = vec_adds(vp->old_metrics->v[i+1],metric);
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m3 = vec_adds(vp->old_metrics->v[9+i],metric);
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m1 = vec_adds(vp->old_metrics->v[9+i],m_metric);
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m2 = vec_adds(vp->old_metrics->v[i+1],m_metric);
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/* Compare and select second set */
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decision0 = vec_cmpgt(m0,m1);
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decision1 = vec_cmpgt(m2,m3);
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survivor0 = vec_min(m0,m1);
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survivor1 = vec_min(m2,m3);
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/* Interleave and store decisions and survivors */
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d->v[2*i+2] = vec_mergeh(decision0,decision1);
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d->v[2*i+3] = vec_mergel(decision0,decision1);
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vp->new_metrics->v[2*i+2] = vec_mergeh(survivor0,survivor1);
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vp->new_metrics->v[2*i+3] = vec_mergel(survivor0,survivor1);
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}
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d++;
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/* renormalize if necessary */
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if(vp->new_metrics->c[0] >= 50){
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int i;
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vector unsigned char scale0,scale1;
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/* Find smallest metric and splat */
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scale0 = vp->new_metrics->v[0];
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scale1 = vp->new_metrics->v[1];
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for(i=2;i<16;i+=2){
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scale0 = vec_min(scale0,vp->new_metrics->v[i]);
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scale1 = vec_min(scale1,vp->new_metrics->v[i+1]);
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}
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scale0 = vec_min(scale0,scale1);
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,8));
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,4));
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,2));
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scale0 = vec_min(scale0,vec_sld(scale0,scale0,1));
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/* Now subtract from all metrics */
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for(i=0;i<16;i++)
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vp->new_metrics->v[i] = vec_subs(vp->new_metrics->v[i],scale0);
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}
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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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