1 files changed, 180 insertions, 0 deletions
diff --git a/viterbi27_sse2.c b/viterbi27_sse2.c
new file mode 100644
index 0000000..bc01710
--- /dev/null
+++ b/viterbi27_sse2.c
@@ -0,0 +1,180 @@
+/* K=7 r=1/2 Viterbi decoder for SSE2
+ * Feb 2004, Phil Karn, KA9Q
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <memory.h>
+#include <xmmintrin.h>
+#include "fec.h"
+
+typedef union { unsigned char c[64]; __m128i v[4]; } metric_t;
+typedef union { unsigned long w[2]; unsigned char c[8]; unsigned short s[4]; __m64 v[1];} decision_t;
+union branchtab27 { unsigned char c[32]; __m128i v[2];} Branchtab27_sse2[2];
+static int Init = 0;
+
+/* State info for instance of Viterbi decoder
+ * Don't change this without also changing references in sse2bfly27.s!
+ */
+struct v27 {
+  metric_t metrics1; /* path metric buffer 1 */
+  metric_t metrics2; /* path metric buffer 2 */
+  decision_t *dp;          /* Pointer to current decision */
+  metric_t *old_metrics,*new_metrics; /* Pointers to path metrics, swapped on every bit */
+  decision_t *decisions;   /* Beginning of decisions for block */
+};
+
+/* Initialize Viterbi decoder for start of new frame */
+int init_viterbi27_sse2(void *p,int starting_state){
+  struct v27 *vp = p;
+  int i;
+
+  if(p == NULL)
+    return -1;
+  for(i=0;i<64;i++)
+    vp->metrics1.c[i] = 63;
+
+  vp->old_metrics = &vp->metrics1;
+  vp->new_metrics = &vp->metrics2;
+  vp->dp = vp->decisions;
+  vp->old_metrics->c[starting_state & 63] = 0; /* Bias known start state */
+  return 0;
+}
+
+void set_viterbi27_polynomial_sse2(int polys[2]){
+  int state;
+
+  for(state=0;state < 32;state++){
+    Branchtab27_sse2[0].c[state] = (polys[0] < 0) ^ parity((2*state) & abs(polys[0])) ? 255 : 0;
+    Branchtab27_sse2[1].c[state] = (polys[1] < 0) ^ parity((2*state) & abs(polys[1])) ? 255 : 0;
+  }
+  Init++;
+}
+
+
+/* Create a new instance of a Viterbi decoder */
+void *create_viterbi27_sse2(int len){
+  void *p;
+  struct v27 *vp;
+
+  if(!Init){
+    int polys[2] = { V27POLYA, V27POLYB };
+    set_viterbi27_polynomial_sse2(polys);
+  }
+  /* Ordinary malloc() only returns 8-byte alignment, we need 16 */
+  if(posix_memalign(&p, sizeof(__m128i),sizeof(struct v27)))
+    return NULL;
+  vp = (struct v27 *)p;
+
+  if((p = malloc((len+6)*sizeof(decision_t))) == NULL){
+    free(vp);
+    return NULL;
+  }
+  vp->decisions = (decision_t *)p;
+  init_viterbi27_sse2(vp,0);
+
+  return vp;
+}
+
+/* Viterbi chainback */
+int chainback_viterbi27_sse2(
+      void *p,
+      unsigned char *data, /* Decoded output data */
+      unsigned int nbits, /* Number of data bits */
+      unsigned int endstate){ /* Terminal encoder state */
+  struct v27 *vp = p;
+  decision_t *d;
+
+  if(p == NULL)
+    return -1;
+  d = vp->decisions;
+  /* Make room beyond the end of the encoder register so we can
+   * accumulate a full byte of decoded data
+   */
+  endstate %= 64;
+  endstate <<= 2;
+
+  /* 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 += 6; /* Look past tail */
+  while(nbits-- != 0){
+    int k;
+
+    k = (d[nbits].c[(endstate>>2)/8] >> ((endstate>>2)%8)) & 1;
+    data[nbits>>3] = endstate = (endstate >> 1) | (k << 7);
+  }
+  return 0;
+}
+
+/* Delete instance of a Viterbi decoder */
+void delete_viterbi27_sse2(void *p){
+  struct v27 *vp = p;
+
+  if(vp != NULL){
+    free(vp->decisions);
+    free(vp);
+  }
+}
+
+
+#if 0
+/* This code is turned off because it's slower than my hand-crafted assembler in sse2bfly27.s. But it does work. */
+void update_viterbi27_blk_sse2(void *p,unsigned char *syms,int nbits){
+  struct v27 *vp = p;
+  decision_t *d;
+
+  if(p == NULL)
+    return;
+  d = (decision_t *)vp->dp;
+  while(nbits--){
+    __m128i sym0v,sym1v;
+    void *tmp;
+    int i;
+    
+    /* Splat the 0th symbol across sym0v, the 1st symbol across sym1v, etc */
+    sym0v = _mm_set1_epi8(syms[0]);
+    sym1v = _mm_set1_epi8(syms[1]);
+    syms += 2;
+
+    for(i=0;i<2;i++){
+      __m128i decision0,decision1,metric,m_metric,m0,m1,m2,m3,survivor0,survivor1;
+
+      /* Form branch metrics */
+      metric = _mm_avg_epu8(_mm_xor_si128(Branchtab27_sse2[0].v[i],sym0v),_mm_xor_si128(Branchtab27_sse2[1].v[i],sym1v));
+      /* There's no packed bytes right shift in SSE2, so we use the word version and mask
+       * (I'm *really* starting to like Altivec...)
+       */
+      metric = _mm_srli_epi16(metric,3);
+      metric = _mm_and_si128(metric,_mm_set1_epi8(31));
+      m_metric = _mm_sub_epi8(_mm_set1_epi8(31),metric);
+    
+      /* Add branch metrics to path metrics */
+      m0 = _mm_add_epi8(vp->old_metrics->v[i],metric);
+      m3 = _mm_add_epi8(vp->old_metrics->v[2+i],metric);
+      m1 = _mm_add_epi8(vp->old_metrics->v[2+i],m_metric);
+      m2 = _mm_add_epi8(vp->old_metrics->v[i],m_metric);
+    
+      /* Compare and select, using modulo arithmetic */
+      decision0 = _mm_cmpgt_epi8(_mm_sub_epi8(m0,m1),_mm_setzero_si128());
+      decision1 = _mm_cmpgt_epi8(_mm_sub_epi8(m2,m3),_mm_setzero_si128());
+      survivor0 = _mm_or_si128(_mm_and_si128(decision0,m1),_mm_andnot_si128(decision0,m0));
+      survivor1 = _mm_or_si128(_mm_and_si128(decision1,m3),_mm_andnot_si128(decision1,m2));
+ 
+      /* Pack each set of decisions into 16 bits */
+      d->s[2*i] = _mm_movemask_epi8(_mm_unpacklo_epi8(decision0,decision1));
+      d->s[2*i+1] = _mm_movemask_epi8(_mm_unpackhi_epi8(decision0,decision1));
+
+      /* Store surviving metrics */
+      vp->new_metrics->v[2*i] = _mm_unpacklo_epi8(survivor0,survivor1);
+      vp->new_metrics->v[2*i+1] = _mm_unpackhi_epi8(survivor0,survivor1);
+    }
+    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;
+}
+#endif