diff options
Diffstat (limited to 'viterbi27_port.c')
| -rw-r--r-- | viterbi27_port.c | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/viterbi27_port.c b/viterbi27_port.c new file mode 100644 index 0000000..7cac2b3 --- /dev/null +++ b/viterbi27_port.c @@ -0,0 +1,191 @@ +/* K=7 r=1/2 Viterbi decoder in portable C + * Copyright Feb 2004, Phil Karn, KA9Q + * May be used under the terms of the GNU Lesser General Public License (LGPL) + */ +#include <stdio.h> +#include <stdlib.h> +#include <memory.h> +#include <limits.h> +#include "fec.h" + + +typedef union { unsigned int w[64]; } metric_t; +typedef union { unsigned long w[2];} decision_t; +static union branchtab27 { unsigned char c[32]; } Branchtab27[2] __attribute__ ((aligned(16))); +static int Init = 0; + +/* State info for instance of Viterbi decoder + * Don't change this without also changing references in [mmx|sse|sse2]bfly29.s! + */ +struct v27 { + metric_t metrics1; /* path metric buffer 1 */ + metric_t metrics2; /* path metric buffer 2 */ + decision_t *dp; /* Pointer to current decision */ + metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */ + decision_t *decisions; /* Beginning of decisions for block */ +}; + +/* Initialize Viterbi decoder for start of new frame */ +int init_viterbi27_port(void *p,int starting_state){ + struct v27 *vp = p; + int i; + + if(p == NULL) + return -1; + for(i=0;i<64;i++) + vp->metrics1.w[i] = 63; + + vp->old_metrics = &vp->metrics1; + vp->new_metrics = &vp->metrics2; + vp->dp = vp->decisions; + vp->old_metrics->w[starting_state & 63] = 0; /* Bias known start state */ + return 0; +} + +void set_viterbi27_polynomial_port(int polys[2]){ + int state; + + for(state=0;state < 32;state++){ + Branchtab27[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0; + Branchtab27[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0; + } + Init++; +} + +/* Create a new instance of a Viterbi decoder */ +void *create_viterbi27_port(int len){ + struct v27 *vp; + + if(!Init){ + int polys[2] = { V27POLYA, V27POLYB }; + set_viterbi27_polynomial_port(polys); + } + if((vp = malloc(sizeof(struct v27))) == NULL) + return NULL; + if((vp->decisions = malloc((len+6)*sizeof(decision_t))) == NULL){ + free(vp); + return NULL; + } + init_viterbi27_port(vp,0); + + return vp; +} + +/* Viterbi chainback */ +int chainback_viterbi27_port( + void *p, + unsigned char *data, /* Decoded output data */ + unsigned int nbits, /* Number of data bits */ + unsigned int endstate){ /* Terminal encoder state */ + struct v27 *vp = p; + decision_t *d; + + if(p == NULL) + return -1; + d = vp->decisions; + /* Make room beyond the end of the encoder register so we can + * accumulate a full byte of decoded data + */ + endstate %= 64; + endstate <<= 2; + + /* The store into data[] only needs to be done every 8 bits. + * But this avoids a conditional branch, and the writes will + * combine in the cache anyway + */ + d += 6; /* Look past tail */ + while(nbits-- != 0){ + int k; + + k = (d[nbits].w[(endstate>>2)/32] >> ((endstate>>2)%32)) & 1; + data[nbits>>3] = endstate = (endstate >> 1) | (k << 7); + } + return 0; +} + +/* Delete instance of a Viterbi decoder */ +void delete_viterbi27_port(void *p){ + struct v27 *vp = p; + + if(vp != NULL){ + free(vp->decisions); + free(vp); + } +} + +/* C-language butterfly */ +#define BFLY(i) {\ +unsigned int metric,m0,m1,decision;\ + metric = (Branchtab27[0].c[i] ^ sym0) + (Branchtab27[1].c[i] ^ sym1);\ + m0 = vp->old_metrics->w[i] + metric;\ + m1 = vp->old_metrics->w[i+32] + (510 - metric);\ + decision = (signed int)(m0-m1) > 0;\ + vp->new_metrics->w[2*i] = decision ? m1 : m0;\ + d->w[i/16] |= decision << ((2*i)&31);\ + m0 -= (metric+metric-510);\ + m1 += (metric+metric-510);\ + decision = (signed int)(m0-m1) > 0;\ + vp->new_metrics->w[2*i+1] = decision ? m1 : m0;\ + d->w[i/16] |= decision << ((2*i+1)&31);\ +} + +/* Update decoder with a block of demodulated symbols + * Note that nbits is the number of decoded data bits, not the number + * of symbols! + */ +int update_viterbi27_blk_port(void *p,unsigned char *syms,int nbits){ + struct v27 *vp = p; + void *tmp; + decision_t *d; + + if(p == NULL) + return -1; + d = (decision_t *)vp->dp; + while(nbits--){ + unsigned char sym0,sym1; + + d->w[0] = d->w[1] = 0; + sym0 = *syms++; + sym1 = *syms++; + + BFLY(0); + BFLY(1); + BFLY(2); + BFLY(3); + BFLY(4); + BFLY(5); + BFLY(6); + BFLY(7); + BFLY(8); + BFLY(9); + BFLY(10); + BFLY(11); + BFLY(12); + BFLY(13); + BFLY(14); + BFLY(15); + BFLY(16); + BFLY(17); + BFLY(18); + BFLY(19); + BFLY(20); + BFLY(21); + BFLY(22); + BFLY(23); + BFLY(24); + BFLY(25); + BFLY(26); + BFLY(27); + BFLY(28); + BFLY(29); + BFLY(30); + BFLY(31); + d++; + /* Swap pointers to old and new metrics */ + tmp = vp->old_metrics; + vp->old_metrics = vp->new_metrics; + vp->new_metrics = tmp; + } + vp->dp = d; + return 0; +} |