210 lines
5.7 KiB
C
210 lines
5.7 KiB
C
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/* K=7 r=1/2 Viterbi decoder for SSE2
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* Feb 2004, Phil Karn, KA9Q
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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 <xmmintrin.h>
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#include "fec.h"
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typedef union {
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unsigned char c[64];
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__m128i v[4];
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} metric_t;
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typedef union {
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unsigned long w[2];
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unsigned char c[8];
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unsigned short s[4];
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__m64 v[1];
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} decision_t;
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union branchtab27 {
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unsigned char c[32];
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__m128i v[2];
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} Branchtab27_sse2[2];
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static int Init = 0;
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/* State info for instance of Viterbi decoder
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* Don't change this without also changing references in sse2bfly27.s!
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*/
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struct v27 {
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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,
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*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_viterbi27_sse2(void *p, int starting_state)
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{
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struct v27 *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 < 64; i++) {
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vp->metrics1.c[i] = 63;
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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->c[starting_state & 63] = 0; /* Bias known start state */
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return 0;
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}
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void set_viterbi27_polynomial_sse2(int polys[2])
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{
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int state;
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for (state = 0; state < 32; state++) {
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Branchtab27_sse2[0].c[state] = (polys[0] < 0) ^ parity((2 * state) & abs(
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polys[0])) ? 255 : 0;
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Branchtab27_sse2[1].c[state] = (polys[1] < 0) ^ parity((2 * state) & abs(
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polys[1])) ? 255 : 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_viterbi27_sse2(int len)
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{
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void *p;
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struct v27 *vp;
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if (!Init) {
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int polys[2] = { V27POLYA, V27POLYB };
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set_viterbi27_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 v27))) {
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return NULL;
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}
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vp = (struct v27 *)p;
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if ((p = malloc((len + 6) * 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_viterbi27_sse2(vp, 0);
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return vp;
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}
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/* Viterbi chainback */
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int chainback_viterbi27_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 v27 *vp = p;
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decision_t *d;
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if (p == NULL) {
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return -1;
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}
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d = 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 %= 64;
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endstate <<= 2;
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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 += 6; /* 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 >> 2) / 8] >> ((endstate >> 2) % 8)) & 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_viterbi27_sse2(void *p)
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{
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struct v27 *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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#if 0
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/* This code is turned off because it's slower than my hand-crafted assembler in sse2bfly27.s. But it does work. */
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void update_viterbi27_blk_sse2(void *p, unsigned char *syms, int nbits)
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{
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struct v27 *vp = p;
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decision_t *d;
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if (p == NULL) {
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return;
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}
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d = (decision_t *)vp->dp;
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while (nbits--) {
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__m128i sym0v, sym1v;
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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_epi8(syms[0]);
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sym1v = _mm_set1_epi8(syms[1]);
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syms += 2;
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for (i = 0; i < 2; 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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metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[i], sym0v),
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_mm_xor_si128(Branchtab27_sse2[1].v[i], sym1v));
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/* There's no packed bytes right shift in SSE2, so we use the word version and mask
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* (I'm *really* starting to like Altivec...)
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*/
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metric = _mm_srli_epi16(metric, 3);
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metric = _mm_and_si128(metric, _mm_set1_epi8(31));
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m_metric = _mm_sub_epi8(_mm_set1_epi8(31), metric);
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/* Add branch metrics to path metrics */
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m0 = _mm_add_epi8(vp->old_metrics->v[i], metric);
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m3 = _mm_add_epi8(vp->old_metrics->v[2 + i], metric);
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m1 = _mm_add_epi8(vp->old_metrics->v[2 + i], m_metric);
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m2 = _mm_add_epi8(vp->old_metrics->v[i], m_metric);
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/* Compare and select, using modulo arithmetic */
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decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0, m1), _mm_setzero_si128());
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decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2, m3), _mm_setzero_si128());
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survivor0 = _mm_or_si128(_mm_and_si128(decision0, m1),
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_mm_andnot_si128(decision0, m0));
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survivor1 = _mm_or_si128(_mm_and_si128(decision1, m3),
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_mm_andnot_si128(decision1, m2));
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/* Pack each set of decisions into 16 bits */
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d->s[2 * i] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0, decision1));
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d->s[2 * i + 1] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0, decision1));
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/* Store surviving metrics */
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vp->new_metrics->v[2 * i] = _mm_unpacklo_epi8(survivor0, survivor1);
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vp->new_metrics->v[2 * i + 1] = _mm_unpackhi_epi8(survivor0, survivor1);
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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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}
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#endif
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