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/* Compute the sum of the squares of a vector of signed shorts
* This is the Altivec SIMD version. It's a little hairy because Altivec
* does not do 64-bit operations directly, so we have to accumulate separate
* 32-bit sums and carries
* Copyright 2004 Phil Karn, KA9Q
* May be used under the terms of the GNU Lesser General Public License (LGPL)
*/
#include "fec.h"
unsigned long long sumsq_av(signed short *in,int cnt){
long long sum;
vector signed short x;
vector unsigned int sums,carries,s1,s2;
int pad;
union { vector unsigned char cv; vector unsigned int iv; unsigned int w[4]; unsigned char c[16];} s;
carries = sums = (vector unsigned int)(0);
if((pad = (int)in & 15)!=0){
/* Load unaligned leading word */
x = vec_perm(vec_ld(0,in),(vector signed short)(0),vec_lvsl(0,in));
if(cnt < 8){ /* Shift right to chop stuff beyond end of short block */
s.c[15] = (8-cnt)<<4;
x = vec_sro(x,s.cv);
}
sums = (vector unsigned int)vec_msum(x,x,(vector signed int)(0));
in += 8-pad/2;
cnt -= 8-pad/2;
}
/* Everything is now aligned, rip through most of the block */
while(cnt >= 8){
x = vec_ld(0,in);
/* A single vec_msum cannot overflow, but we have to sum it with
* the earlier terms separately to handle the carries
* The cast to unsigned is OK because squares are always positive
*/
s1 = (vector unsigned int)vec_msum(x,x,(vector signed int)(0));
carries = vec_add(carries,vec_addc(sums,s1));
sums = vec_add(sums,s1);
in += 8;
cnt -= 8;
}
/* Handle trailing fragment, if any */
if(cnt > 0){
x = vec_ld(0,in);
s.c[15] = (8-cnt)<<4;
x = vec_sro(x,s.cv);
s1 = (vector unsigned int)vec_msum(x,x,(vector signed int)(0));
carries = vec_add(carries,vec_addc(sums,s1));
sums = vec_add(sums,s1);
}
/* Combine 4 sub-sums and carries */
s.c[15] = 64; /* Shift right two 32-bit words */
s1 = vec_sro(sums,s.cv);
s2 = vec_sro(carries,s.cv);
carries = vec_add(carries,vec_addc(sums,s1));
sums = vec_add(sums,s1);
carries = vec_add(carries,s2);
s.c[15] = 32; /* Shift right one 32-bit word */
s1 = vec_sro(sums,s.cv);
s2 = vec_sro(carries,s.cv);
carries = vec_add(carries,vec_addc(sums,s1));
sums = vec_add(sums,s1);
carries = vec_add(carries,s2);
/* Extract sum and carries from right-hand words and combine into result */
s.iv = sums;
sum = s.w[3];
s.iv = carries;
sum += (long long)s.w[3] << 32;
return sum;
}
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