Home | History | Annotate | Download | only in fec
      1 /* K=9 r=1/2 Viterbi decoder for MMX
      2  * Copyright Feb 2004, Phil Karn, KA9Q
      3  * May be used under the terms of the GNU Lesser General Public License (LGPL)
      4  */
      5 #include <stdio.h>
      6 #include <stdlib.h>
      7 #include <memory.h>
      8 #include <mmintrin.h>
      9 #include "fec.h"
     10 
     11 typedef union { char c[256]; __m64 v[32];} decision_t;
     12 typedef union { unsigned char c[256]; __m64 v[32];} metric_t;
     13 
     14 unsigned char Mettab29_1[256][128] __attribute__ ((aligned(8)));
     15 unsigned char Mettab29_2[256][128] __attribute__ ((aligned(8)));
     16 static int Init = 0;
     17 
     18 /* State info for instance of Viterbi decoder
     19  * Don't change this without also changing references in mmxbfly29.s!
     20  */
     21 struct v29 {
     22   metric_t metrics1; /* path metric buffer 1 */
     23   metric_t metrics2; /* path metric buffer 2 */
     24   decision_t *dp;          /* Pointer to current decision */
     25   metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
     26   decision_t *decisions;   /* Beginning of decisions for block */
     27 };
     28 
     29 /* Create a new instance of a Viterbi decoder */
     30 void *create_viterbi29_mmx(int len){
     31   struct v29 *vp;
     32 
     33   if(Init == 0){
     34     int polys[2] = {V29POLYA,V29POLYB};
     35 
     36     set_viterbi29_polynomial_mmx(polys);
     37   }
     38   if((vp = (struct v29 *)malloc(sizeof(struct v29))) == NULL)
     39     return NULL;
     40 
     41   if((vp->decisions = (decision_t *)malloc((len+8)*sizeof(decision_t))) == NULL){
     42     free(vp);
     43     return NULL;
     44   }
     45   init_viterbi29(vp,0);
     46   return vp;
     47 }
     48 
     49 void set_viterbi29_polynomial_mmx(int polys[2]){
     50   int state;
     51 
     52   for(state=0;state < 128;state++){
     53     int symbol;
     54 
     55     for(symbol = 0;symbol < 256;symbol++){
     56       int sym;
     57 
     58       sym = parity((2*state) & abs(polys[0])) ^ (polys[0] < 0);
     59       Mettab29_1[symbol][state] = (sym ? (255-symbol):symbol) / 16;
     60 
     61       sym = parity((2*state) & abs(polys[1])) ^ (polys[1] < 0);
     62       Mettab29_2[symbol][state] = (sym ? (255-symbol):symbol) / 16;
     63     }
     64   }
     65   Init++;
     66 }
     67 
     68 /* Initialize Viterbi decoder for start of new frame */
     69 int init_viterbi29_mmx(void *p,int starting_state){
     70   struct v29 *vp = p;
     71   int i;
     72 
     73   if(p == NULL)
     74     return -1;
     75   for(i=0;i<256;i++)
     76     vp->metrics1.c[i] = 63;
     77 
     78   vp->old_metrics = &vp->metrics1;
     79   vp->new_metrics = &vp->metrics2;
     80   vp->dp = vp->decisions;
     81   vp->old_metrics->c[starting_state & 255] = 0; /* Bias known start state */
     82   return 0;
     83 }
     84 
     85 /* Viterbi chainback */
     86 int chainback_viterbi29_mmx(
     87       void *p,
     88       unsigned char *data, /* Decoded output data */
     89       unsigned int nbits, /* Number of data bits */
     90       unsigned int endstate){ /* Terminal encoder state */
     91 
     92   struct v29 *vp = (struct v29 *)p;
     93   decision_t *d;
     94 
     95   if(p == NULL)
     96     return -1;
     97 
     98   d = (decision_t *)vp->decisions;
     99   endstate &= 255;
    100   d += 8; /* Look past tail */
    101   while(nbits-- != 0){
    102     int k;
    103 
    104     k = d[nbits].c[endstate] & 1;
    105     data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
    106   }
    107   return 0;
    108 }
    109 
    110 /* Delete instance of a Viterbi decoder */
    111 void delete_viterbi29_mmx(void *p){
    112   struct v29 *vp = p;
    113 
    114   if(vp != NULL){
    115     free(vp->decisions);
    116     free(vp);
    117   }
    118 }
    119