SLIWIN_BPW
#define SLIWIN_WORDS howmany(SLIWIN_BITS, SLIWIN_BPW)
uint64_t i = W->T / SLIWIN_BPW;
uint64_t j = S / SLIWIN_BPW;
word = (S / SLIWIN_BPW) % SLIWIN_WORDS;
bit = S % SLIWIN_BPW;