https://github.com/micciancio/SWIFFT
Tip revision: f9b3e55e0bb32eb556f97afa18890a9811d04635 authored by Daniele Micciancio on 11 October 2016, 22:11:12 UTC
typo
typo
Tip revision: f9b3e55
setup.c
#include "swifft.h"
ZN mulTable ALIGN;
ZW fftTable[1<<W] ALIGN;
long center(long x) {
// center(x) = x mod P, |center(x)| <= P/2
long y = ((x % P)+P)%P;
if (y > P/2) y -= P;
return y;
}
int rev(int i, int bound) { // bit reversal permutation
int irev=0;
for(i |= bound; i>1; i>>=1)
irev = (irev<<1) | (i&1);
return irev;
}
int bit(int x, int b) // extract b-th bit of x
{ return (x >> b) & 1; }
void setupTables() {
long omega_pow[2*N]; // the powers of omega
omega_pow[0] = 1;
for(int i = 1; i < 2*N; i++)
omega_pow[i] = center(omega_pow[i-1] * OMEGA);
for (int i=0; i<N/W; i++)
for (int j=0; j<W; j++)
mulTable[i][j] = omega_pow[rev(i,N/W)*(2*j+1)];
for (int x=0; x<(1<<W); x++)
for (int j=0; j<W; j++) {
long tmp = 0;
for (int k=0; k<W; k++)
tmp += omega_pow[((N/W)*(2*j+1)*rev(k,W))%(2*N)]*bit(x,k);
fftTable[x][j] = center(tmp);
}
}
void setupKey(HashKey key) { // Reduce key mod P and initialize keysum
for (int j=0; j<N; j++) {
long sum = 0;
for (int i=0; i<M; i++) {
key.keyval[i][j/W][j%W] = center(key.keyval[i][j/W][j%W]);
sum += key.keyval[i][j/W][j%W];
}
key.keysum[j/W][j%W] = center(sum * ((P-1)/2));
}
}