blob: c516afe8fbb5e8f22643305f2d0b7bd32c0499bc [file] [log] [blame]
 /* 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 #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; }; 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 */ for(i=0;i<4;i++){ dp->coeffs[i] = (signed short *)calloc(1+(len+i-1)/4, 4*sizeof(signed short)); for(j=0;jcoeffs[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; for(i=0;i<4;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_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); }