Numbers

Test for equality of floating point numbers carefully.

IEEE floating point numbers are wrongly over-trusted in calculations.Observe:

  1.     print "---\n";
  2.     print "A: ", 2.4, "\n";
  3.     print "B: ", 0.2*12, "\n";
  4.     if ( 0.2*12 == 2.4 ) {
  5.         print "These are equal.\n";
  6.     }
  7.     else {
  8.         print "These are not equal.\n";
  9.     }
  10.  
  11.     A: 2.4
  12.     B: 2.4
  13.     These are not equal.

This is the result of the fact that 0.2 ( 1/5 ) cannot be represented as a binary fraction in IEEE space.

Thus, if you're checking floating-point equality, use sprintf or similar.

See http://perldoc.perl.org/perlfaq4.html for details.

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