logos-storage/outsourcing-Reed-Solomon
1
0
Fork 0
mirror of https://github.com/logos-storage/outsourcing-Reed-Solomon.git synced 2026-01-02 21:53:09 +00:00
Code Issues Packages Projects Releases Wiki Activity

improve inverse NTT speed by 10% by doing the rescaling only at the end (instead of at every step)

Browse Source
This commit is contained in:
Balazs Komuves 2025-11-05 17:13:18 +01:00
parent 0edb80b6b6
commit 2adca16e10
No known key found for this signature in database
GPG Key ID: F63B7AEF18435562
1 changed files with 9 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
reference/src/cbits/ntt.c
View File

@ -164,8 +164,6 @@ void goldilocks_ntt_inverse_noalloc(int m, int tgt_stride, const uint64_t *gpows
tgt[0 ] = goldilocks_add( src[0] , src[1] ); // x + y
tgt[tgt_stride] = goldilocks_sub( src[0] , src[1] ); // x - y
tgt[0 ] = goldilocks_div_by_2( tgt[0 ] ); // (x + y)/2
tgt[tgt_stride] = goldilocks_div_by_2( tgt[tgt_stride] ); // (x - y)/2
return;
}
@ -177,8 +175,7 @@ void goldilocks_ntt_inverse_noalloc(int m, int tgt_stride, const uint64_t *gpows
uint64_t gpow = gpows[j*tgt_stride];
buf[j ] = goldilocks_add( src[j] , src[j+halfN] ); // x + y
buf[j+halfN] = goldilocks_sub( src[j] , src[j+halfN] ); // x - y
buf[j ] = goldilocks_div_by_2( buf[j ] ); // (x + y) / 2
buf[j+halfN] = goldilocks_mul ( buf[j+halfN] , gpow ); // (x - y) / (2*g^k)
buf[j+halfN] = goldilocks_mul( buf[j+halfN] , gpow ); // (x - y) / g^k
}
goldilocks_ntt_inverse_noalloc( m-1 , tgt_stride<<1 , gpows , buf , buf + N , tgt );
@ -193,10 +190,10 @@ void goldilocks_ntt_inverse(int m, const uint64_t gen, const uint64_t *src, uint
int N = (1<<m);
int halfN = (N>>1);
// precalculate [1/2,g^{-1}/2,g^{-2}/2,g^{-3}/2...]
// precalculate [1,g^{-1},g^{-2},g^{-3}...]
uint64_t *gpows = malloc( 8 * halfN );
assert( gpows != 0 );
uint64_t x = goldilocks_oneHalf; // 1/2
uint64_t x = 1;
uint64_t ginv = goldilocks_inv(gen); // gen^-1
for(int i=0; i<halfN; i++) {
gpows[i] = x;
@ -206,6 +203,12 @@ void goldilocks_ntt_inverse(int m, const uint64_t gen, const uint64_t *src, uint
uint64_t *buf = malloc( 8 * (2*N) );
assert( buf !=0 );
goldilocks_ntt_inverse_noalloc( m, 1, gpows, src, buf, tgt );
uint64_t rescale = goldilocks_inv( N );
for(int i=0; i<N; i++) {
tgt[i] = goldilocks_mul( tgt[i] , rescale );
}
free(buf);
free(gpows);
}