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
peakval_av(signed short * in,int cnt)11 signed 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