in sntrup4591761.c [610:620]
static void small_random_weightw(small *f)
{
crypto_int32 r[p];
int i;
for (i = 0;i < p;++i) r[i] = small_random32();
for (i = 0;i < w;++i) r[i] &= -2;
for (i = w;i < p;++i) r[i] = (r[i] & -3) | 1;
int32_sort(r,p);
for (i = 0;i < p;++i) f[i] = ((small) (r[i] & 3)) - 1;
}