/*
 * An implementation of Conway's Game of Life.
 */
#include "life.h"

static const char * const life_info[] = {
"@(#) $Copyright: (C) 2003 Tony Finch (dot@dotat.at) $",
"@(#) $dotat: life/life.c,v 1.37 2003/12/18 23:31:12 fanf2 Exp $" };

life_cells *
life(life_cells *this, life_cells *new, void *ctx) {
    life_bmp prevL, thisL, nextL, prevR, thisR, nextR;
    life_bmp rear1, rear2, midd1, midd2, fore1, fore2;
    life_bmp bmp, count1, count2, count4a, count4b;
    life_cells *prev, *next;
    life_pos x, y;

    prevL = thisL = nextL = rear1 = rear2 = 0;
    prev = next = this; new->pos = -1;
    for(;;) {
        if(new->pos > -1) ++new;
        if(prev == next) {
            if(next->pos == -1) return(new->pos = -1, ++new);
            y = next++->pos - 1;
        } else {
            if(prev->pos == y++) prev++;
            if(this->pos == y)   this++;
            if(next->pos == y+1) next++;
        }
        new->pos = y;
        for(;;) {             x = prev->pos;
            if(x < this->pos) x = this->pos;
            if(x < next->pos) x = next->pos;
            if(x < 0) break;
            for(;;) {
                if(prev->pos == x) { prevR = prev++->bmp;
                if(this->pos == x)   thisR = this++->bmp; else thisR = 0;
                if(next->pos == x)   nextR = next++->bmp; else nextR = 0;
                } else { prevR = 0;
                if(this->pos == x) { thisR = this++->bmp;
                if(next->pos == x)   nextR = next++->bmp; else nextR = 0;
                } else { thisR = 0;
                if(next->pos == x) { nextR = next++->bmp;
                } else { nextR = 0;
                if(rear1 == 0 && rear2 == 0 &&
                   prevL == 0 && thisL == 0 && nextL == 0) break; } } }
                ADD3(fore1,fore2, prevL << 1 | prevR >> WORDSIZE-1,
                                  thisL << 1 | thisR >> WORDSIZE-1,
                                  nextL << 1 | nextR >> WORDSIZE-1);
                ADD2(midd1,midd2, prevL,nextL);
                ADD3(count1,count2, fore1,midd1,rear1);
                ADD3(count2,count4a, count2,fore2,rear2);
                ADD2(count2,count4b, count2,midd2);
                bmp = (count1 | thisL) & count2 & ~count4a & ~count4b;
                life_draw_bmp(ctx, x+WORDSIZE, y, thisL, bmp);
                if(bmp) ++new, new->pos = x+WORDSIZE, new->bmp = bmp;
                ADD3(rear1,rear2, prevL << WORDSIZE-1 | prevR >> 1,
                                  thisL << WORDSIZE-1 | thisR >> 1,
                                  nextL << WORDSIZE-1 | nextR >> 1);
                prevL = prevR; thisL = thisR; nextL = nextR; x -= WORDSIZE;
            }
        }
    }
}