| /* 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; |

| } |

| |