216 lines
5.8 KiB
C
216 lines
5.8 KiB
C
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/* K=9 r=1/3 Viterbi decoder for x86 MMX
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* 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 <mmintrin.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 "fec.h"
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typedef union {
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unsigned char c[256];
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__m64 v[32];
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} decision_t;
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typedef union {
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unsigned short s[256];
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__m64 v[64];
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} metric_t;
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static union branchtab39 {
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unsigned short s[128];
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__m64 v[32];
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} 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,
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*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_mmx(void *p, int starting_state)
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{
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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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}
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for (i = 0; i < 256; i++) {
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vp->metrics1.s[i] = 1000;
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}
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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] = 0; /* Bias known start state */
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return 0;
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}
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void set_viterbi39_polynomial_mmx(int polys[3])
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{
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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
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: 0;
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Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2 * state) & polys[1]) ? 255
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: 0;
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Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2 * state) & polys[2]) ? 255
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: 0;
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}
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Init++;
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}
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/* Create a new instance of a Viterbi decoder */
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void *create_viterbi39_mmx(int len)
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{
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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_mmx(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_mmx(vp, 0);
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return vp;
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}
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/* Viterbi chainback */
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int chainback_viterbi39_mmx(
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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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{
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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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}
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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].c[endstate] & 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;
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}
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/* Delete instance of a Viterbi decoder */
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void delete_viterbi39_mmx(void *p)
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{
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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_mmx(void *p, unsigned char *syms, int nbits)
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{
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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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}
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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,
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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 0-1530
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*/
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m0 = _mm_add_pi16(_mm_xor_si64(Branchtab39[0].v[i], sym0v),
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_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_add_pi16(vp->old_metrics->v[i], metric);
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m3 = _mm_add_pi16(vp->old_metrics->v[32 + i], metric);
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m1 = _mm_add_pi16(vp->old_metrics->v[32 + i], m_metric);
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m2 = _mm_add_pi16(vp->old_metrics->v[i], m_metric);
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/* Compare and select
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* There's no packed min instruction in MMX, so we use modulo arithmetic
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* to form the decisions and then do the select the hard way
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*/
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decision0 = _mm_cmpgt_pi16(_mm_sub_pi16(m0, m1), _mm_setzero_si64());
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decision1 = _mm_cmpgt_pi16(_mm_sub_pi16(m2, m3), _mm_setzero_si64());
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survivor0 = _mm_or_si64(_mm_and_si64(decision0, m1), _mm_andnot_si64(decision0,
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m0));
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survivor1 = _mm_or_si64(_mm_and_si64(decision1, m3), _mm_andnot_si64(decision1,
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m2));
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/* Merge decisions and store as bytes */
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d->v[i] = _mm_unpacklo_pi8(_mm_packs_pi16(decision0, _mm_setzero_si64()),
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_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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if (vp->new_metrics->s[0] < vp->old_metrics->s[0]) {
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path_metric += 65536; /* Hack: wraparound probably occured */
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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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