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