[Israel.pm] math problem

Yossi.Itzkovich at ecitele.com Yossi.Itzkovich at ecitele.com
Sun Nov 13 02:46:52 PST 2005


Hi,

already discussed here few time.  It's float precision problem. I think the
problem is inherited from C.

Yossi



                                                                                                                                       
                      "Yishay Weiss"                                                                                                   
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                      13/11/2005 12:43                                                                                                 
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Hi,

This here is so basic I can't imagine it wasn't discussed before. Still,
does anyone care to tell me what's going on here? Can perl be failing to
subtract properly?

I run this script: (perl 5.8.4 on windows XP, but I also tried it with
5.8.0
on Linux)

========

$a = 0.3847;
$b = 0.4303;
$c = 0.0456;

$result = $b - $c;

print "a: $a\nresult: $result\n";
print "a == result ? ". ($a == $result)."\n";

=====

and I get:

=====

a: 0.3847
result: 0.3847
a == result ?

=======

Which is wrong. Then I run the same script with slightly bigger numbers:

========

$a = 0.3847 * 10;
$b = 0.4303 * 10;
$c = 0.0456 * 10;

$result = $b - $c;

print "a: $a\nresult: $result\n";
print "a == result ? ". ($a == $result)."\n";

=========

and get:

========

a: 3.847
result: 3.847
a == result ? 1

=======

Which makes perfect sense. Any ideas?

Yishay


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