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
13unsigned 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