mirror of https://github.com/PentHertz/srsLTE.git
283 lines
7.5 KiB
C
283 lines
7.5 KiB
C
/* Adapted Phil Karn's r=1/3 k=9 viterbi decoder to r=1/3 k=7
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*
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* 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 <stdio.h>
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#include <stdint.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 "parity.h"
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//#define DEBUG
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#ifdef LV_HAVE_SSE
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#include <emmintrin.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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} Branchtab37_sse2[3];
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/* State info for instance of Viterbi decoder */
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struct v37 {
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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,*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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void set_viterbi37_polynomial_sse(uint32_t polys[3]) {
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int state;
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for(state=0;state < 32;state++){
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Branchtab37_sse2[0].c[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0;
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Branchtab37_sse2[1].c[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0;
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Branchtab37_sse2[2].c[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0;
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}
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}
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/* Initialize Viterbi decoder for start of new frame */
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int init_viterbi37_sse(void *p, int starting_state) {
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struct v37 *vp = p;
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uint32_t i;
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for(i=0;i<64;i++)
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vp->metrics1.c[i] = 63;
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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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if (starting_state != -1) {
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vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */
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}
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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_viterbi37_sse(uint32_t polys[3], uint32_t len) {
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void *p;
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struct v37 *vp;
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set_viterbi37_polynomial_sse(polys);
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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 v37)))
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return NULL;
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vp = (struct v37 *)p;
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if(posix_memalign(&p, sizeof(__m128i),(len+6)*sizeof(decision_t))) {
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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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return vp;
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}
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/* Viterbi chainback */
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int chainback_viterbi37_sse(
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void *p,
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uint8_t *data, /* Decoded output data */
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uint32_t nbits, /* Number of data bits */
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uint32_t endstate) { /* Terminal encoder state */
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struct v37 *vp = p;
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if (p == NULL)
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return -1;
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decision_t *d = (decision_t *)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--) {
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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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endstate = (endstate >> 1) | (k << 7);
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data[nbits] = k;
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//printf("nbits=%d, endstate=%3d, k=%d, w[0]=%d, w[1]=%d, c=%d\n", nbits, endstate, k, d[nbits].s[1]&1, d[nbits].s[2]&1, d[nbits].c[(endstate>>2)/8]&1);
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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_viterbi37_sse(void *p){
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struct v37 *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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void print_128i(char *s, __m128i val) {
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printf("%s: ", s);
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uint8_t *x = (uint8_t*) &val;
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for (int i=0;i<16;i++) {
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printf("%3d, ", x[i]);
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}
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printf("\n");
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}
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void update_viterbi37_blk_sse(void *p,unsigned char *syms,int nbits, uint32_t *best_state) {
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struct v37 *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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#ifdef DEBUG
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printf("[");
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#endif
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d = (decision_t *) vp->dp;
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for (int s=0;s<nbits;s++) {
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memset(d+s,0,sizeof(decision_t));
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}
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while(nbits--) {
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__m128i sym0v,sym1v,sym2v;
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void *tmp;
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int i;
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// printf("nbits=%d, syms=%d,%d,%d\n", nbits, syms[0], syms[1], syms[2]);fflush(stdout);
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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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sym2v = _mm_set1_epi8(syms[2]);
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syms += 3;
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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,survivor1;
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/* Form branch metrics */
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m0 = _mm_avg_epu8(_mm_xor_si128(Branchtab37_sse2[0].v[i],sym0v),_mm_xor_si128(Branchtab37_sse2[1].v[i],sym1v));
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metric = _mm_avg_epu8(_mm_xor_si128(Branchtab37_sse2[2].v[i],sym2v),m0);
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#ifdef DEBUG
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print_128i("metric_initial", metric);
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#endif
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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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*/
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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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#ifdef DEBUG
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print_128i("metric ", metric);
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print_128i("m_metric ", m_metric);
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#endif
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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),_mm_andnot_si128(decision0,m0));
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survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_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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// See if we need to normalize
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if (vp->new_metrics->c[0] > 100) {
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int i;
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uint8_t adjust;
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__m128i adjustv;
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union { __m128i v; signed short w[8]; } t;
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adjustv = vp->new_metrics->v[0];
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for(i=1;i<4;i++) {
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adjustv = _mm_min_epu8(adjustv,vp->new_metrics->v[i]);
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}
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adjustv = _mm_min_epu8(adjustv,_mm_srli_si128(adjustv,8));
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adjustv = _mm_min_epu8(adjustv,_mm_srli_si128(adjustv,4));
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adjustv = _mm_min_epu8(adjustv,_mm_srli_si128(adjustv,2));
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t.v = adjustv;
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adjust = t.w[0];
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adjustv = _mm_set1_epi8(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<4;i++)
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vp->new_metrics->v[i] = _mm_sub_epi8(vp->new_metrics->v[i],adjustv);
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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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if (best_state) {
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uint32_t i, bst=0;
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uint8_t minmetric=UINT8_MAX;
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for (i=0;i<64;i++) {
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if (vp->old_metrics->c[i] <= minmetric) {
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bst = i;
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minmetric = vp->old_metrics->c[i];
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}
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}
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*best_state = bst;
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}
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#ifdef DEBUG
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printf("];\n===========================================\n");
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#endif
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vp->dp = d;
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}
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#endif
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