would moving from to involve passing between two consecutive segments of the same worm? */
| 895 | /* would moving from <x1,y1> to <x2,y2> involve passing between two |
| 896 | consecutive segments of the same worm? */ |
| 897 | boolean |
| 898 | worm_cross(int x1, int y1, int x2, int y2) |
| 899 | { |
| 900 | struct monst *worm; |
| 901 | struct wseg *curr, *wnxt; |
| 902 | |
| 903 | /* |
| 904 | * With digits representing relative sequence number of the segments, |
| 905 | * returns true when testing between @ and ? (passes through worm's |
| 906 | * body), false between @ and ! (stays on same side of worm). |
| 907 | * .w1?.. |
| 908 | * ..@2.. |
| 909 | * .65!3. |
| 910 | * ...4.. |
| 911 | */ |
| 912 | |
| 913 | if (distmin(x1, y1, x2, y2) != 1) { |
| 914 | impossible("worm_cross checking for non-adjacent location?"); |
| 915 | return FALSE; |
| 916 | } |
| 917 | /* attempting to pass between worm segs is only relevant for diagonal */ |
| 918 | if (x1 == x2 || y1 == y2) |
| 919 | return FALSE; |
| 920 | |
| 921 | /* is the same monster at <x1,y2> and at <x2,y1>? */ |
| 922 | worm = m_at(x1, y2); |
| 923 | if (!worm || m_at(x2, y1) != worm) |
| 924 | return FALSE; |
| 925 | |
| 926 | /* same monster is at both adjacent spots, so must be a worm; we need |
| 927 | to figure out if the two spots are occupied by consecutive segments */ |
| 928 | for (curr = wtails[worm->wormno]; curr; curr = wnxt) { |
| 929 | wnxt = curr->nseg; |
| 930 | if (!wnxt) |
| 931 | break; /* no next segment; can't continue */ |
| 932 | |
| 933 | /* we don't know which of <x1,y2> or <x2,y1> we'll hit first, but |
| 934 | whichever it is, they're consecutive iff next seg is the other */ |
| 935 | if (curr->wx == x1 && curr->wy == y2) |
| 936 | return (boolean) (wnxt->wx == x2 && wnxt->wy == y1); |
| 937 | if (curr->wx == x2 && curr->wy == y1) |
| 938 | return (boolean) (wnxt->wx == x1 && wnxt->wy == y2); |
| 939 | } |
| 940 | /* should never reach here... */ |
| 941 | return FALSE; |
| 942 | } |
| 943 | |
| 944 | /* construct an index number for a worm tail segment */ |
| 945 | int |