intersect
memset(intersect, 0, sizeof(intersect));
ip = &intersect[FAREA * FAREA];
extern short intersect[FAREA * FAREA]; /* frame [a][b] intersection */
short intersect[FAREA * FAREA]; /* frame [a][b] intersection */
intersect[a * FAREA + b] = n = sp - board;
intersect[b * FAREA + a] = n;
intersect[a * FAREA + b] = n = esp - board;
intersect[b * FAREA + a] = n;
ip = &intersect[n];
intersect(bchans, btxpow, &nb, gchans, gtxpow, ng);
intersect(tchans, ttxpow, &nt, achans, atxpow, na);
intersect(tgchans, tgtxpow, &ntg, gchans, gtxpow, ng);
intersect(gchans, gtxpow, &ng, nchans, ntxpow, nn);
intersect(achans, atxpow, &na, nchans, ntxpow, nn);