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-rw-r--r--viterbi39_mmx.c185
1 files changed, 185 insertions, 0 deletions
diff --git a/viterbi39_mmx.c b/viterbi39_mmx.c
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+/* K=9 r=1/3 Viterbi decoder for x86 MMX
+ * Aug 2006, Phil Karn, KA9Q
+ * May be used under the terms of the GNU Lesser General Public License (LGPL)
+ */
+#include <mmintrin.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <memory.h>
+#include "fec.h"
+
+typedef union { unsigned char c[256]; __m64 v[32];} decision_t;
+typedef union { unsigned short s[256]; __m64 v[64];} metric_t;
+
+static union branchtab39 { unsigned short s[128]; __m64 v[32];} Branchtab39[3];
+static int Init = 0;
+
+/* State info for instance of Viterbi decoder */
+struct v39 {
+ metric_t metrics1; /* path metric buffer 1 */
+ metric_t metrics2; /* path metric buffer 2 */
+ void *dp; /* Pointer to current decision */
+ metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
+ void *decisions; /* Beginning of decisions for block */
+};
+
+/* Initialize Viterbi decoder for start of new frame */
+int init_viterbi39_mmx(void *p,int starting_state){
+ struct v39 *vp = p;
+ int i;
+
+ if(p == NULL)
+ return -1;
+ for(i=0;i<256;i++)
+ vp->metrics1.s[i] = 1000;
+
+ vp->old_metrics = &vp->metrics1;
+ vp->new_metrics = &vp->metrics2;
+ vp->dp = vp->decisions;
+ vp->old_metrics->s[starting_state & 255] = 0; /* Bias known start state */
+ return 0;
+}
+
+void set_viterbi39_polynomial_mmx(int polys[3]){
+ int state;
+
+ for(state=0;state < 128;state++){
+ Branchtab39[0].s[state] = (polys[0] < 0) ^ parity((2*state) & polys[0]) ? 255:0;
+ Branchtab39[1].s[state] = (polys[1] < 0) ^ parity((2*state) & polys[1]) ? 255:0;
+ Branchtab39[2].s[state] = (polys[2] < 0) ^ parity((2*state) & polys[2]) ? 255:0;
+ }
+ Init++;
+}
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi39_mmx(int len){
+ struct v39 *vp;
+
+ if(!Init){
+ int polys[3] = { V39POLYA,V39POLYB,V39POLYC };
+ set_viterbi39_polynomial_mmx(polys);
+ }
+ if((vp = (struct v39 *)malloc(sizeof(struct v39))) == NULL)
+ return NULL;
+ if((vp->decisions = malloc((len+8)*sizeof(decision_t))) == NULL){
+ free(vp);
+ return NULL;
+ }
+ init_viterbi39_mmx(vp,0);
+ return vp;
+}
+
+
+
+/* Viterbi chainback */
+int chainback_viterbi39_mmx(
+ void *p,
+ unsigned char *data, /* Decoded output data */
+ unsigned int nbits, /* Number of data bits */
+ unsigned int endstate){ /* Terminal encoder state */
+ struct v39 *vp = p;
+ decision_t *d;
+ int path_metric;
+
+ if(p == NULL)
+ return -1;
+
+ d = (decision_t *)vp->decisions;
+
+ endstate %= 256;
+
+ path_metric = vp->old_metrics->s[endstate];
+
+ /* 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 += 8; /* Look past tail */
+ while(nbits-- != 0){
+ int k;
+
+ k = d[nbits].c[endstate] & 1;
+ endstate = (k << 7) | (endstate >> 1);
+ data[nbits>>3] = endstate;
+ }
+ return path_metric;
+}
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi39_mmx(void *p){
+ struct v39 *vp = p;
+
+ if(vp != NULL){
+ free(vp->decisions);
+ free(vp);
+ }
+}
+
+
+int update_viterbi39_blk_mmx(void *p,unsigned char *syms,int nbits){
+ struct v39 *vp = p;
+ decision_t *d;
+ int path_metric = 0;
+
+ if(p == NULL)
+ return -1;
+
+ d = (decision_t *)vp->dp;
+
+ while(nbits--){
+ __m64 sym0v,sym1v,sym2v;
+ void *tmp;
+ int i;
+
+ /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
+ sym0v = _mm_set1_pi16(syms[0]);
+ sym1v = _mm_set1_pi16(syms[1]);
+ sym2v = _mm_set1_pi16(syms[2]);
+ syms += 3;
+
+ for(i=0;i<32;i++){
+ __m64 decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
+
+ /* Form branch metrics
+ * Because Branchtab takes on values 0 and 255, and the values of sym?v are offset binary in the range 0-255,
+ * the XOR operations constitute conditional negation.
+ * metric and m_metric (-metric) are in the range 0-1530
+ */
+ m0 = _mm_add_pi16(_mm_xor_si64(Branchtab39[0].v[i],sym0v),_mm_xor_si64(Branchtab39[1].v[i],sym1v));
+ metric = _mm_add_pi16(_mm_xor_si64(Branchtab39[2].v[i],sym2v),m0);
+ m_metric = _mm_sub_pi16(_mm_set1_pi16(765),metric);
+
+ /* Add branch metrics to path metrics */
+ m0 = _mm_add_pi16(vp->old_metrics->v[i],metric);
+ m3 = _mm_add_pi16(vp->old_metrics->v[32+i],metric);
+ m1 = _mm_add_pi16(vp->old_metrics->v[32+i],m_metric);
+ m2 = _mm_add_pi16(vp->old_metrics->v[i],m_metric);
+
+ /* Compare and select
+ * There's no packed min instruction in MMX, so we use modulo arithmetic
+ * to form the decisions and then do the select the hard way
+ */
+ decision0 = _mm_cmpgt_pi16(_mm_sub_pi16(m0,m1),_mm_setzero_si64());
+ decision1 = _mm_cmpgt_pi16(_mm_sub_pi16(m2,m3),_mm_setzero_si64());
+ survivor0 = _mm_or_si64(_mm_and_si64(decision0,m1),_mm_andnot_si64(decision0,m0));
+ survivor1 = _mm_or_si64(_mm_and_si64(decision1,m3),_mm_andnot_si64(decision1,m2));
+
+ /* Merge decisions and store as bytes */
+ d->v[i] = _mm_unpacklo_pi8(_mm_packs_pi16(decision0,_mm_setzero_si64()),_mm_packs_pi16(decision1,_mm_setzero_si64()));
+
+ /* Store surviving metrics */
+ vp->new_metrics->v[2*i] = _mm_unpacklo_pi16(survivor0,survivor1);
+ vp->new_metrics->v[2*i+1] = _mm_unpackhi_pi16(survivor0,survivor1);
+ }
+ if(vp->new_metrics->s[0] < vp->old_metrics->s[0])
+ path_metric += 65536; /* Hack: wraparound probably occured */
+ 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;
+ _mm_empty();
+ return path_metric;
+}