SEI CERT Perl Coding Standard

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3 Comments

  1. thiago glauco sanchez

    Like others languages, is not a good idea compare floating point numbers in Perl. For solving that you can:

    transform the numbers in strings and compare the strings according hte precision needs of yours:

    sub are_equals {

    #dont forget to sanitize $num1 and $num2 before using into sprintf

        my ($num1, $num2, $precision) = @_;

        return sprintf("%.${precision}f", $num1) eq sprintf("%.${precision}f", $num2);

    }

     

    define an acceptable error range ($delta) for your project:

    sub are_equals {

        my ($num1, $num2, $delta) = @_;

        if ( $delta >= ($num1 - $num2) )

            return 1;

        return 0; }

     

    Or just use bignum accordingly.

    1. David Svoboda

      Yes, there is a world of information on how to handle floating-point arithmetic. IIRC the Perl FAQ has some info. Also CERT has plenty of info on their C wiki:  Rule 05. Floating Point (FLP). Since most languages use IEEE 754 for fp arithmetic, mostly the do's and dont's are language-independent (smile)

    2. Anonymous

      You'll have troubles if $num1 is "too much" less than $num2 (think calling are_equals(0, 2, 1)).

       

      abs() helps here:

      sub are_equals {

          my ($num1, $num2, $delta) = @_;

          if ( $delta >= abs($num1 - $num2) )

              return 1;

          return 0; }

       

      I also find it more readable to put the difference in the left hand side and call $delta with a more expressive (IMHO) name:

      sub are_equals {

          my ($num1, $num2, $max_delta) = @_;

          return abs($num1 - $num2) <= $max_delta;

      }