237 lines
6.9 KiB
C
237 lines
6.9 KiB
C
/* K=15 r=1/6 Viterbi decoder for x86 SSE2
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* Copyright Mar 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 <emmintrin.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 {
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unsigned long w[512];
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unsigned short s[1024];
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} decision_t;
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typedef union {
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signed short s[16384];
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__m128i v[2048];
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} metric_t;
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static union branchtab615 {
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unsigned short s[8192];
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__m128i v[1024];
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} Branchtab615[6];
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static int Init = 0;
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/* State info for instance of Viterbi decoder */
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struct v615 {
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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_viterbi615_sse2(void *p, int starting_state)
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{
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struct v615 *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 < 16384; i++) {
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vp->metrics1.s[i] = (SHRT_MIN + 5000);
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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 & 16383] =
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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_viterbi615_sse2(int len)
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{
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void *p;
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struct v615 *vp;
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if (!Init) {
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int polys[6] = { V615POLYA, V615POLYB, V615POLYC, V615POLYD, V615POLYE, V615POLYF };
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set_viterbi615_polynomial_sse2(polys);
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}
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/* Ordinary malloc() only returns 8-byte alignment, we need 16 */
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if (posix_memalign(&p, sizeof(__m128i), sizeof(struct v615))) {
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return NULL;
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}
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vp = (struct v615 *)p;
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if ((p = malloc((len + 14) * sizeof(decision_t))) == NULL) {
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free(vp);
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return NULL;
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}
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vp->decisions = (decision_t *)p;
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init_viterbi615_sse2(vp, 0);
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return vp;
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}
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void set_viterbi615_polynomial_sse2(int polys[6])
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{
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int state;
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int i;
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for (state = 0; state < 8192; state++) {
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for (i = 0; i < 6; i++) {
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Branchtab615[i].s[state] = (polys[i] < 0) ^ parity((2 * state) & abs(
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polys[i])) ? 255 : 0;
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}
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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_viterbi615_sse2(
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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 v615 *vp = p;
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decision_t *d = (decision_t *)vp->decisions;
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endstate %= 16384;
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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 += 14; /* 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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endstate = (k << 13) | (endstate >> 1);
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data[nbits >> 3] = endstate >> 6;
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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_viterbi615_sse2(void *p)
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{
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struct v615 *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_viterbi615_blk_sse2(void *p, unsigned char *syms, int nbits)
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{
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struct v615 *vp = p;
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decision_t *d = (decision_t *)vp->dp;
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while (nbits--) {
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__m128i sym0v, sym1v, sym2v, sym3v, sym4v, sym5v;
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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_epi16(syms[0]);
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sym1v = _mm_set1_epi16(syms[1]);
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sym2v = _mm_set1_epi16(syms[2]);
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sym3v = _mm_set1_epi16(syms[3]);
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sym4v = _mm_set1_epi16(syms[4]);
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sym5v = _mm_set1_epi16(syms[5]);
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syms += 6;
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/* SSE2 doesn't support saturated adds on unsigned shorts, so we have to use signed shorts */
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for (i = 0; i < 1024; i++) {
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__m128i 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_epi16(_mm_xor_si128(Branchtab615[0].v[i], sym0v),
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_mm_xor_si128(Branchtab615[1].v[i], sym1v));
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m1 = _mm_add_epi16(_mm_xor_si128(Branchtab615[2].v[i], sym2v),
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_mm_xor_si128(Branchtab615[3].v[i], sym3v));
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m2 = _mm_add_epi16(_mm_xor_si128(Branchtab615[4].v[i], sym4v),
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_mm_xor_si128(Branchtab615[5].v[i], sym5v));
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metric = _mm_add_epi16(m0, _mm_add_epi16(m1, m2));
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m_metric = _mm_sub_epi16(_mm_set1_epi16(1530), metric);
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/* Add branch metrics to path metrics */
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m0 = _mm_adds_epi16(vp->old_metrics->v[i], metric);
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m3 = _mm_adds_epi16(vp->old_metrics->v[1024 + i], metric);
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m1 = _mm_adds_epi16(vp->old_metrics->v[1024 + i], m_metric);
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m2 = _mm_adds_epi16(vp->old_metrics->v[i], m_metric);
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/* Compare and select */
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survivor0 = _mm_min_epi16(m0, m1);
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survivor1 = _mm_min_epi16(m2, m3);
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decision0 = _mm_cmpeq_epi16(survivor0, m1);
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decision1 = _mm_cmpeq_epi16(survivor1, m3);
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/* Pack each set of decisions into 8 8-bit bytes, then interleave them and compress into 16 bits */
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d->s[i] = _mm_movemask_epi8(_mm_unpacklo_epi8(_mm_packs_epi16(decision0,
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_mm_setzero_si128()), _mm_packs_epi16(decision1, _mm_setzero_si128())));
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/* Store surviving metrics */
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vp->new_metrics->v[2 * i] = _mm_unpacklo_epi16(survivor0, survivor1);
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vp->new_metrics->v[2 * i + 1] = _mm_unpackhi_epi16(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 0-90 branch metrics is 405
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*/
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if (vp->new_metrics->s[0] >= SHRT_MAX - 12750) {
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int i, adjust;
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__m128i adjustv;
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union {
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__m128i v;
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signed short w[8];
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} 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 < 2048; i++) {
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adjustv = _mm_min_epi16(adjustv, vp->new_metrics->v[i]);
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}
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adjustv = _mm_min_epi16(adjustv, _mm_srli_si128(adjustv, 8));
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adjustv = _mm_min_epi16(adjustv, _mm_srli_si128(adjustv, 4));
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adjustv = _mm_min_epi16(adjustv, _mm_srli_si128(adjustv, 2));
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t.v = adjustv;
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adjust = t.w[0] - SHRT_MIN;
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adjustv = _mm_set1_epi16(adjust);
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/* We cannot use a saturated subtract, because we often have to adjust by more than SHRT_MAX
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* This is okay since it can't overflow anyway
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*/
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for (i = 0; i < 2048; i++) {
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vp->new_metrics->v[i] = _mm_sub_epi16(vp->new_metrics->v[i], adjustv);
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}
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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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return 0;
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}
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