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 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
