1 /* 16-bit signed integer dot product
2 * MMX assisted version; also for SSE
3 *
4 * Copyright 2004 Phil Karn
5 * May be used under the terms of the GNU Lesser General Public License (LGPL)
6 */
7 #include <stdlib.h>
8 #include "fec.h"
9
10 struct dotprod {
11 int len; /* Number of coefficients */
12
13 /* On a MMX or SSE machine, these hold 4 copies of the coefficients,
14 * preshifted by 0,1,2,3 words to meet all possible input data
15 * alignments (see Intel ap559 on MMX dot products).
16 */
17 signed short *coeffs[4];
18 };
19 long dotprod_mmx_assist(signed short *a,signed short *b,int cnt);
20
21 /* Create and return a descriptor for use with the dot product function */
initdp_mmx(signed short coeffs[],int len)22 void *initdp_mmx(signed short coeffs[],int len){
23 struct dotprod *dp;
24 int i,j;
25
26
27 if(len == 0)
28 return NULL;
29
30 dp = (struct dotprod *)calloc(1,sizeof(struct dotprod));
31 dp->len = len;
32
33 /* Make 4 copies of coefficients, one for each data alignment */
34 for(i=0;i<4;i++){
35 dp->coeffs[i] = (signed short *)calloc(1+(len+i-1)/4,
36 4*sizeof(signed short));
37 for(j=0;j<len;j++)
38 dp->coeffs[i][j+i] = coeffs[j];
39 }
40 return (void *)dp;
41 }
42
43
44 /* Free a dot product descriptor created earlier */
freedp_mmx(void * p)45 void freedp_mmx(void *p){
46 struct dotprod *dp = (struct dotprod *)p;
47 int i;
48
49 for(i=0;i<4;i++)
50 if(dp->coeffs[i] != NULL)
51 free(dp->coeffs[i]);
52 free(dp);
53 }
54
55 /* Compute a dot product given a descriptor and an input array
56 * The length is taken from the descriptor
57 */
dotprod_mmx(void * p,signed short a[])58 long dotprod_mmx(void *p,signed short a[]){
59 struct dotprod *dp = (struct dotprod *)p;
60 int al;
61 signed short *ar;
62
63 /* Round input data address down to 8 byte boundary
64 * NB: depending on the alignment of a[], memory
65 * before a[] will be accessed. The contents don't matter since they'll
66 * be multiplied by zero coefficients. I can't conceive of any
67 * situation where this could cause a segfault since memory protection
68 * in the x86 machines is done on much larger boundaries
69 */
70 ar = (signed short *)((int)a & ~7);
71
72 /* Choose one of 4 sets of pre-shifted coefficients. al is both the
73 * index into dp->coeffs[] and the number of 0 words padded onto
74 * that coefficients array for alignment purposes
75 */
76 al = a - ar;
77
78 /* Call assembler routine to do the work, passing number of 4-word blocks */
79 return dotprod_mmx_assist(ar,dp->coeffs[al],(dp->len+al-1)/4+1);
80 }
81
82