1 /* Compute the sum of the squares of a vector of signed shorts
2
3 * This is the Altivec SIMD version. It's a little hairy because Altivec
4 * does not do 64-bit operations directly, so we have to accumulate separate
5 * 32-bit sums and carries
6
7 * Copyright 2004 Phil Karn, KA9Q
8 * May be used under the terms of the GNU Lesser General Public License (LGPL)
9 */
10
11 #include "fec.h"
12
sumsq_av(signed short * in,int cnt)13 unsigned long long sumsq_av(signed short *in,int cnt){
14 long long sum;
15 vector signed short x;
16 vector unsigned int sums,carries,s1,s2;
17 int pad;
18 union { vector unsigned char cv; vector unsigned int iv; unsigned int w[4]; unsigned char c[16];} s;
19
20 carries = sums = (vector unsigned int)(0);
21 if((pad = (int)in & 15)!=0){
22 /* Load unaligned leading word */
23 x = vec_perm(vec_ld(0,in),(vector signed short)(0),vec_lvsl(0,in));
24 if(cnt < 8){ /* Shift right to chop stuff beyond end of short block */
25 s.c[15] = (8-cnt)<<4;
26 x = vec_sro(x,s.cv);
27 }
28 sums = (vector unsigned int)vec_msum(x,x,(vector signed int)(0));
29 in += 8-pad/2;
30 cnt -= 8-pad/2;
31 }
32 /* Everything is now aligned, rip through most of the block */
33 while(cnt >= 8){
34 x = vec_ld(0,in);
35 /* A single vec_msum cannot overflow, but we have to sum it with
36 * the earlier terms separately to handle the carries
37 * The cast to unsigned is OK because squares are always positive
38 */
39 s1 = (vector unsigned int)vec_msum(x,x,(vector signed int)(0));
40 carries = vec_add(carries,vec_addc(sums,s1));
41 sums = vec_add(sums,s1);
42 in += 8;
43 cnt -= 8;
44 }
45 /* Handle trailing fragment, if any */
46 if(cnt > 0){
47 x = vec_ld(0,in);
48 s.c[15] = (8-cnt)<<4;
49 x = vec_sro(x,s.cv);
50 s1 = (vector unsigned int)vec_msum(x,x,(vector signed int)(0));
51 carries = vec_add(carries,vec_addc(sums,s1));
52 sums = vec_add(sums,s1);
53 }
54 /* Combine 4 sub-sums and carries */
55 s.c[15] = 64; /* Shift right two 32-bit words */
56 s1 = vec_sro(sums,s.cv);
57 s2 = vec_sro(carries,s.cv);
58 carries = vec_add(carries,vec_addc(sums,s1));
59 sums = vec_add(sums,s1);
60 carries = vec_add(carries,s2);
61
62 s.c[15] = 32; /* Shift right one 32-bit word */
63 s1 = vec_sro(sums,s.cv);
64 s2 = vec_sro(carries,s.cv);
65 carries = vec_add(carries,vec_addc(sums,s1));
66 sums = vec_add(sums,s1);
67 carries = vec_add(carries,s2);
68
69 /* Extract sum and carries from right-hand words and combine into result */
70 s.iv = sums;
71 sum = s.w[3];
72
73 s.iv = carries;
74 sum += (long long)s.w[3] << 32;
75
76 return sum;
77 }
78
79