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/* 16-bit signed integer dot product
* MMX assisted version; also for SSE
* 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 a MMX or SSE machine, these hold 4 copies of the coefficients,
* preshifted by 0,1,2,3 words to meet all possible input data
* alignments (see Intel ap559 on MMX dot products).
signed short *coeffs[4];
long dotprod_mmx_assist(signed short *a,signed short *b,int cnt);
/* Create and return a descriptor for use with the dot product function */
void *initdp_mmx(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 4 copies of coefficients, one for each data alignment */
dp->coeffs[i] = (signed short *)calloc(1+(len+i-1)/4,
4*sizeof(signed short));
dp->coeffs[i][j+i] = coeffs[j];
return (void *)dp;
/* Free a dot product descriptor created earlier */
void freedp_mmx(void *p){
struct dotprod *dp = (struct dotprod *)p;
int i;
if(dp->coeffs[i] != NULL)
/* Compute a dot product given a descriptor and an input array
* The length is taken from the descriptor
long dotprod_mmx(void *p,signed short a[]){
struct dotprod *dp = (struct dotprod *)p;
int al;
signed short *ar;
/* Round input data address down to 8 byte boundary
* NB: depending on the alignment of a[], memory
* before a[] will be accessed. The contents don't matter since they'll
* be multiplied by zero coefficients. I can't conceive of any
* situation where this could cause a segfault since memory protection
* in the x86 machines is done on much larger boundaries
ar = (signed short *)((int)a & ~7);
/* Choose one of 4 sets of pre-shifted coefficients. al is both the
* index into dp->coeffs[] and the number of 0 words padded onto
* that coefficients array for alignment purposes
al = a - ar;
/* Call assembler routine to do the work, passing number of 4-word blocks */
return dotprod_mmx_assist(ar,dp->coeffs[al],(dp->len+al-1)/4+1);