261947 - Floating point arithmetics can produce wrong results

Status: RESOLVED DUPLICATE of bug 20140

(Core :: JavaScript Engine, defect)

Description

[escaillas]

User-Agent:       Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)
Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)

A simple operation like :
  2.00000000000001 - 1
produces
  1.0000000000000102

If the 15th digit of a float is not relevant, the comparison operator should not
take it into account as in :
  1 == (1 / 54 + 1) * 54 - 54
wich resolves to :
  1 == 1.000000000000007


Reproducible: Always
Steps to Reproduce:
1. document.write( 1 == (1 / 54 + 1) * 54 - 54 )
2.
3.

Actual Results:  
false

Expected Results:  
true


CPU is AMD Athlon 1.2 Ghz

Comment 1

[Chris Thomas (CTho) [formerly [e-mail] [e-mail]]]

printf("%99.99f\n", (1.0/54.0 + 1.0) * 54.0 - 54.0);
1.000000000000007105427357601001858711242675781250000000000000000000000000000000000000000000000000000

Your issue is with IEEE754 rules, not Mozilla.

Comment 2

[Chris Thomas (CTho) [formerly [e-mail] [e-mail]]]

*** This bug has been marked as a duplicate of 20140 ***