🚀 go-pugleaf

    Well, just after I finished with the update article, I began modifying
  the graphics routines for the DSI-32 virtual graphics library.  I decided
  to substitute the included line drawing routine with the DDA routine
  show here.  After I coded it, I tested it for speed and such just by timing
  (no pixel mapping routines included, just the calculations).  To my suprise,
  I got the wrong answer.  I converted it to fortran and got the right answer,
  so I tested it on the VAX here, and also got the right answer with the same
  identical C code - 20001.5.
    My C gives me 19893.5 !
  If anyone out there can run this on there DSI and get the right results,
  please tell me (I've got the December 1985 dated compilers).

  Thanks,
   John Krist
   {allegra,ihnp4}!{noao,ut-sally}!utastro!jk  

  DDA line drawing code:

     
#include <math.h>
#include <stdio.h>
main()

{
      float x1,x2,y1,y2,rlength,xinc,yinc,x,y;
      int i;

      x1=0.;
      x2=20000.;
      y1=0.;
      y2=20000.;

      rlength = fabs ( x2-x1 );
      if (fabs( y2-y1 ) > rlength )
         rlength = fabs ( y2-y1 );

      xinc = ( x2-x1 ) / rlength;
      yinc = ( y2-y1 ) / rlength;
      x = x1 + .5;
      y = y1 + .5;

      while ( i <= rlength )
       {
        x = x + xinc;
        y = y + yinc;
        i++;
       }
       printf ("%.6f\n",x);
}