init commit

dotprod_av.c

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+/* 16-bit signed integer dot product
+ * Altivec-assisted version
+ * Copyright 2004 Phil Karn
+ * May be used under the terms of the GNU Lesser General Public License (LGPL)
+ */
+#include <stdlib.h>
+#include "fec.h"
+
+struct dotprod {
+  int len; /* Number of coefficients */
+
+  /* On an Altivec machine, these hold 8 copies of the coefficients,
+   * preshifted by 0,1,..7 words to meet all possible input data
+   */
+  signed short *coeffs[8];
+};
+
+/* Create and return a descriptor for use with the dot product function */
+void *initdp_av(signed short coeffs[],int len){
+  struct dotprod *dp;
+  int i,j;
+
+  if(len == 0)
+    return NULL;
+
+  dp = (struct dotprod *)calloc(1,sizeof(struct dotprod));
+  dp->len = len;
+
+  /* Make 8 copies of coefficients, one for each data alignment,
+   * each aligned to 16-byte boundary
+   */
+  for(i=0;i<8;i++){
+    dp->coeffs[i] = calloc(1+(len+i-1)/8,sizeof(vector signed short));
+    for(j=0;j<len;j++)
+      dp->coeffs[i][j+i] = coeffs[j];
+  }
+  return (void *)dp;
+}
+
+
+/* Free a dot product descriptor created earlier */
+void freedp_av(void *p){
+  struct dotprod *dp = (struct dotprod *)p;
+  int i;
+
+  for(i=0;i<8;i++)
+    if(dp->coeffs[i] != NULL)
+      free(dp->coeffs[i]);
+  free(dp);
+}
+
+/* Compute a dot product given a descriptor and an input array
+ * The length is taken from the descriptor
+ */
+long dotprod_av(void *p,signed short a[]){
+  struct dotprod *dp = (struct dotprod *)p;
+  int al;
+  vector signed short *ar,*d;
+  vector signed int sums0,sums1,sums2,sums3;
+  union { vector signed int v; signed int w[4];} s;
+  int nblocks;
+    
+  /* round ar down to beginning of 16-byte block containing 0th element of
+   * input buffer. Then set d to one of 8 sets of shifted coefficients
+   */
+  ar = (vector signed short *)((int)a & ~15);
+  al = ((int)a & 15)/sizeof(signed short);
+  d = (vector signed short *)dp->coeffs[al];
+  
+  nblocks = (dp->len+al-1)/8+1;
+  
+  /* Sum into four vectors each holding four 32-bit partial sums */
+  sums3 = sums2 = sums1 = sums0 = (vector signed int)(0);
+  while(nblocks >= 4){
+    sums0 = vec_msums(ar[nblocks-1],d[nblocks-1],sums0);
+    sums1 = vec_msums(ar[nblocks-2],d[nblocks-2],sums1);
+    sums2 = vec_msums(ar[nblocks-3],d[nblocks-3],sums2);
+    sums3 = vec_msums(ar[nblocks-4],d[nblocks-4],sums3);
+    nblocks -= 4;
+  }
+  sums0 = vec_adds(sums0,sums1);
+  sums2 = vec_adds(sums2,sums3);
+  sums0 = vec_adds(sums0,sums2);
+  while(nblocks-- > 0){
+    sums0 = vec_msums(ar[nblocks],d[nblocks],sums0);
+  }
+  /* Sum 4 partial sums into final result */
+  s.v = vec_sums(sums0,(vector signed int)(0));
+  
+  return s.w[3];
+}
+
+