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82 lines
2.3 KiB
82 lines
2.3 KiB
4 months ago
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/* 16-bit signed integer dot product
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* MMX assisted version; also for SSE
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*
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* Copyright 2004 Phil Karn
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* May be used under the terms of the GNU Lesser General Public License (LGPL)
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*/
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#include <stdlib.h>
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#include "fec.h"
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struct dotprod {
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int len; /* Number of coefficients */
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/* On a MMX or SSE machine, these hold 4 copies of the coefficients,
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* preshifted by 0,1,2,3 words to meet all possible input data
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* alignments (see Intel ap559 on MMX dot products).
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*/
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signed short *coeffs[4];
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};
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long dotprod_mmx_assist(signed short *a,signed short *b,int cnt);
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/* Create and return a descriptor for use with the dot product function */
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void *initdp_mmx(signed short coeffs[],int len){
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struct dotprod *dp;
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int i,j;
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if(len == 0)
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return NULL;
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dp = (struct dotprod *)calloc(1,sizeof(struct dotprod));
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dp->len = len;
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/* Make 4 copies of coefficients, one for each data alignment */
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for(i=0;i<4;i++){
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dp->coeffs[i] = (signed short *)calloc(1+(len+i-1)/4,
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4*sizeof(signed short));
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for(j=0;j<len;j++)
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dp->coeffs[i][j+i] = coeffs[j];
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}
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return (void *)dp;
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}
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/* Free a dot product descriptor created earlier */
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void freedp_mmx(void *p){
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struct dotprod *dp = (struct dotprod *)p;
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int i;
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for(i=0;i<4;i++)
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if(dp->coeffs[i] != NULL)
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free(dp->coeffs[i]);
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free(dp);
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}
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/* Compute a dot product given a descriptor and an input array
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* The length is taken from the descriptor
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*/
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long dotprod_mmx(void *p,signed short a[]){
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struct dotprod *dp = (struct dotprod *)p;
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int al;
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signed short *ar;
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/* Round input data address down to 8 byte boundary
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* NB: depending on the alignment of a[], memory
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* before a[] will be accessed. The contents don't matter since they'll
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* be multiplied by zero coefficients. I can't conceive of any
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* situation where this could cause a segfault since memory protection
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* in the x86 machines is done on much larger boundaries
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*/
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ar = (signed short *)((int)a & ~7);
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/* Choose one of 4 sets of pre-shifted coefficients. al is both the
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* index into dp->coeffs[] and the number of 0 words padded onto
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* that coefficients array for alignment purposes
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*/
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al = a - ar;
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/* Call assembler routine to do the work, passing number of 4-word blocks */
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return dotprod_mmx_assist(ar,dp->coeffs[al],(dp->len+al-1)/4+1);
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}
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