use Perl

• floating point numbers are only equal by luck (Score:2, Interesting)

  by jmm (276)

  Floating point numbers are not exact, and they get more inexact as you work with them. (In Kernghan and Plauger, they say "floating point numbers are like piles of sand - every time you move the pile, you lose a bit of sand and pickup a bit of dirt".)

  Instead of comparing for exact equality, check that they are relatively close. I.e. instead of:

  if ( $x == 0.329 ) ...

  use:

  if( abs($x-0.329) 1e-7 ) ...
  • Re:floating point numbers are only equal by luck (Score:1)

    by exeunt (319)

    I get a syntax error, are you sure you got that right?
    • Re:floating point numbers are only equal by luck (Score:1)

      by bart (450)

      The < sign got dropped. This is HTML...
• It's not just perl... (Score:3, Informative)

  by runrig (3385) <dougwNO@SPAMcpan.org> on 2003.03.11 14:47 (#17877) Journal

  I had to explain this to a java programmer not long ago. Try this to see what's going on:

  printf("%.20f\n", 72.9/100);

  Reply to This

  • Re:It's not just perl... (Score:1)

    by exeunt (319)

    Yeah, MJD sent me another email in private with printf "%.40f", $f to see what is going on... :)
• There's no such thing as 0.1! (Score:2)

  by merlyn (47)

  Amazingly enough, something as simple as 0.1 has no exact IEEE floating point representation!

  --
  

  • Randal L. Schwartz
  • Stonehenge