[Tcl-bugs] [ tcl-Bugs-1152828 ] wrong expr result

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Bugs item #1152828, was opened at 2005-02-27 10:37
Message generated for change (Comment added) made by dkf
You can respond by visiting: 
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Category: 16. Commands A-H
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Donal K. Fellows (dkf)
Summary: wrong expr result

Initial Comment:
the following steps yield a wrong expr result:
% expr (2.13 - 1.97) - (2.115 - 1.955)
-2.22044604925e-16

expected results is 0.0.

Error occures for also for different numbers

Running on tclsh8.3 and tclsh8.4.9 (latest)

emails: ro...@me...
            al...@me...


Thanks

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>Comment By: Donal K. Fellows (dkf)
Date: 2005-03-02 22:18

Message:
Logged In: YES 
user_id=79902

Floating-point numbers are not generally great at
representing arbitrary decimal numbers, so the differences
in a case like this can be signficant. Witness, where we're
using [format] to force a more detailed display of the
actual values involved.:
  % format %.17f [expr 2.115-1.955]
  0.16000000000000014
  % format %.17f [expr 2.13-1.97]
  0.15999999999999992

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