Initial code
diff --git a/viterbi39_sse2.c b/viterbi39_sse2.c
new file mode 100644
index 0000000..f13794e
--- /dev/null
+++ b/viterbi39_sse2.c
@@ -0,0 +1,200 @@
+/* K=15 r=1/6 Viterbi decoder for x86 SSE2
+ * Copyright Mar 2004, Phil Karn, KA9Q
+ * May be used under the terms of the GNU Lesser General Public License (LGPL)
+ */
+#include <emmintrin.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <memory.h>
+#include <limits.h>
+#include "fec.h"
+
+typedef union { unsigned long w[8]; unsigned short s[16];} decision_t;
+typedef union { signed short s[256]; __m128i v[32];} metric_t;
+
+static union branchtab39 { unsigned short s[128]; __m128i v[16];} 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_sse2(void *p,int starting_state){
+ struct v39 *vp = p;
+ int i;
+
+ for(i=0;i<256;i++)
+ vp->metrics1.s[i] = (SHRT_MIN+1000);
+
+ vp->old_metrics = &vp->metrics1;
+ vp->new_metrics = &vp->metrics2;
+ vp->dp = vp->decisions;
+ vp->old_metrics->s[starting_state & 255] = SHRT_MIN; /* Bias known start state */
+ return 0;
+}
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi39_sse2(int len){
+ void *p;
+ struct v39 *vp;
+
+ if(!Init){
+ int polys[3] = { V39POLYA, V39POLYB, V39POLYC };
+
+ set_viterbi39_polynomial_sse2(polys);
+ }
+ /* Ordinary malloc() only returns 8-byte alignment, we need 16 */
+ if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v39)))
+ return NULL;
+
+ vp = (struct v39 *)p;
+ if((p = malloc((len+8)*sizeof(decision_t))) == NULL){
+ free(vp);
+ return NULL;
+ }
+ vp->decisions = (decision_t *)p;
+ init_viterbi39_sse2(vp,0);
+ return vp;
+}
+
+void set_viterbi39_polynomial_sse2(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++;
+}
+
+/* Viterbi chainback */
+int chainback_viterbi39_sse2(
+ 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 = (decision_t *)vp->decisions;
+ int path_metric;
+
+ 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].w[endstate/32] >> (endstate%32)) & 1;
+ endstate = (k << 7) | (endstate >> 1);
+ data[nbits>>3] = endstate;
+ }
+ return path_metric;
+}
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi39_sse2(void *p){
+ struct v39 *vp = p;
+
+ if(vp != NULL){
+ free(vp->decisions);
+ free(vp);
+ }
+}
+
+
+int update_viterbi39_blk_sse2(void *p,unsigned char *syms,int nbits){
+ struct v39 *vp = p;
+ decision_t *d = (decision_t *)vp->dp;
+ int path_metric = 0;
+
+ while(nbits--){
+ __m128i sym0v,sym1v,sym2v;
+ void *tmp;
+ int i;
+
+ /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
+ sym0v = _mm_set1_epi16(syms[0]);
+ sym1v = _mm_set1_epi16(syms[1]);
+ sym2v = _mm_set1_epi16(syms[2]);
+ syms += 3;
+
+ /* SSE2 doesn't support saturated adds on unsigned shorts, so we have to use signed shorts */
+ for(i=0;i<16;i++){
+ __m128i 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 0-765
+ */
+ m0 = _mm_add_epi16(_mm_xor_si128(Branchtab39[0].v[i],sym0v),_mm_xor_si128(Branchtab39[1].v[i],sym1v));
+ metric = _mm_add_epi16(_mm_xor_si128(Branchtab39[2].v[i],sym2v),m0);
+ m_metric = _mm_sub_epi16(_mm_set1_epi16(765),metric);
+
+ /* Add branch metrics to path metrics */
+ m0 = _mm_adds_epi16(vp->old_metrics->v[i],metric);
+ m3 = _mm_adds_epi16(vp->old_metrics->v[16+i],metric);
+ m1 = _mm_adds_epi16(vp->old_metrics->v[16+i],m_metric);
+ m2 = _mm_adds_epi16(vp->old_metrics->v[i],m_metric);
+
+ /* Compare and select */
+ survivor0 = _mm_min_epi16(m0,m1);
+ survivor1 = _mm_min_epi16(m2,m3);
+ decision0 = _mm_cmpeq_epi16(survivor0,m1);
+ decision1 = _mm_cmpeq_epi16(survivor1,m3);
+
+ /* Pack each set of decisions into 8 8-bit bytes, then interleave them and compress into 16 bits */
+ d->s[i] = _mm_movemask_epi8(_mm_unpacklo_epi8(_mm_packs_epi16(decision0,_mm_setzero_si128()),_mm_packs_epi16(decision1,_mm_setzero_si128())));
+
+ /* Store surviving metrics */
+ vp->new_metrics->v[2*i] = _mm_unpacklo_epi16(survivor0,survivor1);
+ vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi16(survivor0,survivor1);
+ }
+ /* See if we need to renormalize */
+ if(vp->new_metrics->s[0] >= SHRT_MAX-5000){
+ int i,adjust;
+ __m128i adjustv;
+ union { __m128i v; signed short w[8]; } t;
+
+ /* Find smallest metric and set adjustv to bring it down to SHRT_MIN */
+ adjustv = vp->new_metrics->v[0];
+ for(i=1;i<32;i++)
+ adjustv = _mm_min_epi16(adjustv,vp->new_metrics->v[i]);
+
+ adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,8));
+ adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,4));
+ adjustv = _mm_min_epi16(adjustv,_mm_srli_si128(adjustv,2));
+ t.v = adjustv;
+ adjust = t.w[0] - SHRT_MIN;
+ path_metric += adjust;
+ adjustv = _mm_set1_epi16(adjust);
+
+ /* We cannot use a saturated subtract, because we often have to adjust by more than SHRT_MAX
+ * This is okay since it can't overflow anyway
+ */
+ for(i=0;i<32;i++)
+ vp->new_metrics->v[i] = _mm_sub_epi16(vp->new_metrics->v[i],adjustv);
+ }
+ 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;
+ return path_metric;
+}
+
+
