jfw@eddie.MIT.EDU (John Woods) (11/27/88)
I have found a rather extensive bug in fall.c. The manifestation is that
screen 3 was insoluble, because I kept getting hit by falling boulders
while ABOVE them. It turns out that fall.c has a number of references to
screen[y{+/-}1][x{+/-}1], where there is no check that the resulting subscript
is in range (hence it was looking at screen[16][1], where 15 is the maximum
subscript. I was unlucky enough to have an @ at that memory location :-).
Enclosed below is a replacement for fall.c, which I believe is equivalent to
the intent of the original (though I confess that the code is rather confusing
to me, for it seems more tortuous than is required. On the other hand, perhaps
I am too sleep-deprived thanks to my new daughter:-). The result appears to
behave the same (less the buggy behavior) on those few tests that I have tried.
I have sent mail to Steven Shipway, but I think the mail bounced (the
uncertainty is courtesy of a singularly unhelpful message from someone's mailer
about not being able to create dfA99999...).
---------------snip----------snip----------------snip-----------------------
#include "wand_head.h"
extern void draw_symbol();
extern int debug_disp;
extern char screen[NOOFROWS][ROWLEN+1];
int check(mx,my,x,y,dx,dy,sx,sy,howdead)
/* check for any falling caused by something moving out of x,y along
vector dx,dy. All the others are constant and should really have
been global... */
int x,y,sx,sy,dx,dy, *mx, *my;
char howdead[25];
{
int ret=0;
ret+=fall(mx,my,x,y,sx,sy,howdead);
ret+=fall(mx,my,x-dx,y-dy,sx,sy,howdead);
ret+=fall(mx,my,x-dy,y-dx,sx,sy,howdead);
ret+=fall(mx,my,x+dy,y+dx,sx,sy,howdead);
ret+=fall(mx,my,x-dx-dy,y-dy-dx,sx,sy,howdead);
ret+=fall(mx,my,x-dx+dy,y-dy+dx,sx,sy,howdead);
return ret;
}
int fall(mx,my,x,y,sx,sy,howdead) /* recursive function for falling */
/* boulders and arrows */
int x,y,sx,sy, *mx, *my;
char howdead[25];
{
int nx = x,nxu = x,nyl = y,nyr = y,retval = 0;
int firstrow = 0, firstcol = 0, lastrow = 0, lastcol = 0;
if ((y>(NOOFROWS-1))||(y<0)||(x<0)||(x>(ROWLEN-1)))
return(0);
if((screen[y][x] != 'O') && (screen[y][x] != ' ') && (screen[y][x] != 'M') &&
(screen[y][x] !='\\') && (screen[y][x] != '/') && (screen[y][x] != '@') &&
(screen[y][x] != '^'))
return(0);
firstrow = (y == 0); lastrow = (y == NOOFROWS-1);
firstcol = (x == 0); lastcol = (x == ROWLEN - 1);
if(screen[y][x] == 'O')
{
int blankright = 0, blankleft = 0, blankabove = 0, blankbelow = 0,
blankupright = 0, blankupleft = 0, blankdnright = 0, blankdnleft = 0;
/* blanks above? */
if (!firstrow)
{
if (!firstcol) blankupleft = (screen[y-1][x-1] == ' ');
blankabove = (screen[y-1][x] == ' ');
if (!lastcol) blankupright = (screen[y-1][x+1] == ' ');
}
/* blanks left and right? */
if (!firstcol) blankleft = (screen[y][x-1] == ' ');
if (!lastcol) blankright = (screen[y][x+1] == ' ');
/* blanks below? */
if (!lastrow)
{
if (!firstcol) blankdnleft = (screen[y+1][x-1] == ' ');
blankbelow = (screen[y+1][x] == ' ');
if (!lastcol) blankdnright = (screen[y+1][x+1] == ' ');
}
if(blankleft && blankupleft)
nx--;
else
{
if(blankright && blankupright)
nx++;
else
nx = -1;
}
if(blankleft && blankdnleft)
nxu--;
else
{
if(blankright && blankdnright)
nxu++;
else
nxu = -1;
}
if(blankabove && blankupright)
nyr--;
else
{
if(blankbelow && blankdnright)
nyr++;
else
nyr = -1;
}
if (blankabove && blankupleft)
nyl--;
else
{
if(blankbelow && blankdnleft)
nyl++;
else
nyl = -1;
}
}
if(screen[y][x] == '\\')
{
if(nx != -1
&& (firstrow || nx == (ROWLEN-1) || screen[y-1][++nx] != ' '))
nx = -1;
if(nxu != -1
&& (lastrow || nxu == 0 || screen[y+1][--nxu] != ' '))
nxu = -1;
if(nyr != -1
&& (lastcol || nyr == 0 || screen[--nyr][x+1] != ' '))
nyr = -1;
if(nyl != -1
&& (firstcol || nyl == (NOOFROWS-1) || screen[++nyl][x-1] != ' '))
nyl = -1;
}
if(screen[y][x] == '/')
{
if(nx != -1
&& (firstrow || nx == 0 || screen[y-1][--nx] != ' '))
nx = -1;
if(nxu != -1
&& (lastrow || nxu == (ROWLEN-1) || screen[y+1][++nxu] != ' '))
nxu = -1;
if(nyr != -1
&& (lastcol || nyr == (NOOFROWS-1) || screen[++nyr][x+1] != ' '))
nyr = -1;
if(nyl != -1
&& (firstcol || nyl == 0 || screen[--nyl][x-1] != ' '))
nyl = -1;
}
if(nx != -1 && (screen[y][nx] != ' ') && (screen[y][nx] != 'M'))
nx = -1;
if((y > 0) && (screen[y-1][x] == 'O') && (nx >= 0) &&
(screen[y][nx] != '^')) /* boulder falls ? */
{
screen[y-1][x] = ' ';
if(screen[y][nx] == '@')
{
strcpy(howdead,"a falling boulder");
retval=1;
}
if(screen[y][nx] == 'M')
{
*mx = *my = -2;
screen[y][nx] = ' ';
}
screen[y][nx] = 'O';
if(!debug_disp)
{
if((y<(sy+5)) && (y>(sy-3)) && (x>(sx-6)) && (x<(sx+6)))
draw_symbol((x-sx+5)*3,(y-sy+2)*2,' ');
if((y<(sy+4)) && (y>(sy-4)) && (nx>(sx-6)) && (nx<(sx+6)))
draw_symbol((nx-sx+5)*3,(y-sy+3)*2,'O');
}
else
{
move(y,x+1);
addch(' ');;
move(y+1,nx+1);
addch('O');
}
refresh();
retval+=fall(mx,my,nx ,y+1,sx,sy,howdead);
retval+=check(mx,my,x,y-1,0,1,sx,sy,howdead);
if(y < NOOFROWS-1 && screen[y+1][nx] == '@')
{
strcpy(howdead,"a falling boulder");
return(1);
}
if(y < NOOFROWS-1 && screen[y+1][nx] == 'M')
{
*mx = *my = -2;
screen[y+1][nx] = ' ';
}
}
if(nyr != -1
&& (screen[nyr][x] != '^')&&(screen[nyr][x] != ' ')&&(screen[nyr][x] != 'M'))
nyr = -1;
if(x+1<ROWLEN && screen[y][x+1] == '<' && nyr >= 0) /* arrow moves ( < ) ? */
{
screen[y][x+1] = ' ';
if(screen[nyr][x] == '@')
{
strcpy(howdead,"a speeding arrow");
retval = 1;
}
if(screen[nyr][x] == 'M')
{
*mx = *my = -2;
screen[nyr][x] = ' ';
}
screen[nyr][x] = '<';
if(!debug_disp)
{
if((y<(sy+4)) && (y>(sy-4)) && (x<(sx+5)) && (x>(sx-7)))
draw_symbol((x-sx+6)*3,(y-sy+3)*2,' ');
if((nyr<(sy+4)) && (nyr>(sy-4)) && (x<(sx+6)) && (x>(sx-6)))
draw_symbol((x-sx+5)*3,(nyr-sy+3)*2,'<');
}
else
{
move(y+1,x+2);
addch(' ');
move(nyr+1,x+1);
addch('<');
}
refresh();
retval+=fall(mx,my,x-1,nyr,sx,sy,howdead);
retval+=check(mx,my,x+1,y,-1,0,sx,sy,howdead);
if(x != 0 && screen[nyr][x-1] == '@')
{
strcpy(howdead,"a speeding arrow");
return(1);
}
if(x != 0 && screen[nyr][x-1] == 'M')
{
*mx = *my = -2;
screen[nyr][x-1] = ' ';
}
}
if(nyl != -1
&& (screen[nyl][x] != ' ')&&(screen[nyl][x] != '^')&&(screen[nyl][x] != 'M'))
nyl = -1;
if(x>0 && (screen[y][x-1] == '>') && nyl>=0) /* arrow moves ( > ) ? */
{
screen[y][x-1] = ' ';
if(screen[nyl][x] == '@')
{
strcpy(howdead,"a speeding arrow");
retval = 1;
}
if(screen[nyl][x] == 'M')
{
*mx = *my = -2;
screen[nyl][x] = ' ';
}
screen[nyl][x] = '>';
if(!debug_disp)
{
if((y<(sy+4)) && (y>(sy-4)) && (x<(sx+7)) && (x>(sx-5)))
draw_symbol((x-sx+4)*3,(y-sy+3)*2,' ');
if((nyl<(sy+4)) && (nyl>(sy-4)) && (x<(sx+6)) && (x>(sx-6)))
draw_symbol((x-sx+5)*3,(nyl-sy+3)*2,'>');
}
else
{
move(y+1,x);
addch(' ');
move(nyl+1,x+1);
addch('>');
}
refresh();
retval+=fall(mx,my,x+1,nyl,sx,sy,howdead);
retval+=check(mx,my,x-1,y,1,0,sx,sy,howdead);
if(!lastcol && screen[nyl][x+1] == '@')
{
strcpy(howdead,"a speeding arrow");
return(1);
}
if(!lastcol && screen[nyl][x+1] == 'M')
{
*mx = *my = -2;
screen[nyl][x+1] = ' ';
}
}
if(nxu != -1 && screen[y][nxu] != ' ')
nxu = -1;
if(y < NOOFROWS-1 && (screen[y+1][x] == '^') && (nxu >= 0) &&
(screen[y][x] != '^')) /* balloon rises? */
{
screen[y+1][x] = ' ';
screen[y][nxu] = '^';
if(!debug_disp)
{
if((y<(sy+3)) && (y>(sy-5)) && (x>(sx-6)) && (x<(sx+6)))
draw_symbol((x-sx+5)*3,(y-sy+4)*2,' ');
if((y<(sy+4)) && (y>(sy-4)) && (nxu>(sx-6)) && (nxu<(sx+6)))
draw_symbol((nxu-sx+5)*3,(y-sy+3)*2,'^');
}
else
{
move(y+2,x+1);
addch(' ');
move(y+1,nxu+1);
addch('^');
}
refresh();
retval+=fall(mx,my,nxu ,y-1,sx,sy,howdead);
retval+=check(mx,my,x,y+1,0,-1,sx,sy,howdead);
}
if(retval>0)
return(1);
return(0);
}
--------pins----------------pins----------------pins------------------------
--
John Woods, Charles River Data Systems, (617) 626-1101
jfw@eddie.MIT.EDU, john@frog.UUCP, ...!decvax!frog!john