1/* Return the largest absolute value of a vector of signed shorts
2
3 * This is the Altivec SIMD version.
4
5 * Copyright 2004 Phil Karn, KA9Q
6 * May be used under the terms of the GNU Lesser General Public License (LGPL)
7 */
8
9#include "fec.h"
10
11signed short peakval_av(signed short *in,int cnt){
12  vector signed short x;
13  int pad;
14  union { vector signed char cv; vector signed short hv; signed short s[8]; signed char c[16];} s;
15  vector signed short smallest,largest;
16
17  smallest = (vector signed short)(0);
18  largest = (vector signed short)(0);
19  if((pad = (int)in & 15)!=0){
20    /* Load unaligned leading word */
21    x = vec_perm(vec_ld(0,in),(vector signed short)(0),vec_lvsl(0,in));
22    if(cnt < 8){ /* Shift right to chop stuff beyond end of short block */
23      s.c[15] = (8-cnt)<<4;
24      x = vec_sro(x,s.cv);
25    }
26    smallest = vec_min(smallest,x);
27    largest = vec_max(largest,x);
28    in += 8-pad/2;
29    cnt -= 8-pad/2;
30  }
31  /* Everything is now aligned, rip through most of the block */
32  while(cnt >= 8){
33    x = vec_ld(0,in);
34    smallest = vec_min(smallest,x);
35    largest = vec_max(largest,x);
36    in += 8;
37    cnt -= 8;
38  }
39  /* Handle trailing fragment, if any */
40  if(cnt > 0){
41    x = vec_ld(0,in);
42    s.c[15] = (8-cnt)<<4;
43    x = vec_sro(x,s.cv);
44    smallest = vec_min(smallest,x);
45    largest = vec_max(largest,x);
46  }
47  /* Combine and extract result */
48  largest = vec_max(largest,vec_abs(smallest));
49
50  s.c[15] = 64; /* Shift right four 16-bit words */
51  largest = vec_max(largest,vec_sro(largest,s.cv));
52
53  s.c[15] = 32; /* Shift right two 16-bit words */
54  largest = vec_max(largest,vec_sro(largest,s.cv));
55
56  s.c[15] = 16; /* Shift right one 16-bit word */
57  largest = vec_max(largest,vec_sro(largest,s.cv));
58
59  s.hv = largest;
60  return s.s[7];
61}
62