Beefy Boxes and Bandwidth Generously Provided by pair Networks
Keep It Simple, Stupid
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

I'm familiar with potential problems with floating point inequality when the values are the results of some computation. But if I assign 1.2345 to $var_a and then assign 1.2345 to $var_b, then perform the equality check, I would expect them to be equal. Direct assignments should not cause different floating point representations, as far as I know.

Once that value is used in any sort of arithmetic, all bets are off.

As an additional test, I wrote a short script (which I should have done earlier, but it still doesn't really explain anything):

#!/usr/bin/perl use strict; use warnings; my %values; while (my $line = <DATA>) { if ($line =~ /(\w)_(r|ch)ange\s(\S+)/) { $values{$1}{$2."ange"} = $3; } } for my $ key(sort keys %values) { if ($values{$key}{'change'} != $values{$key}{'range'}) { print "Not "; } print "Equal:\nChange: $values{$key}{change}\nRange : $values{$key +}{range}\n\n"; } __DATA__ var_a_change 101.945484 var_a_range 101.945484 var_b_change -80.5498336616321 var_b_range -80.5498336616321 var_c_change 45142.388774415 var_c_range 45142.388774415 var_d_change -159.905028384 var_d_range -159.905028384 var_e_change -159.905028384 var_e_range -159.905028384 var_f_change 181.019658002611 var_f_range 181.019658002611 var_g_change 1.57615706403821 var_g_range 1.57615706403821

Every single comparison there passes the equality check. And the only thing this script is doing differently than my actual script is reading the values from Excel. That may be key, I don't know.


In reply to Re^2: False positive on inequality comparison by Nkuvu
in thread False positive on inequality comparison by Nkuvu

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others musing on the Monastery: (2)
As of 2021-11-28 12:57 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found

    Notices?