Arithmetic errors with LOG10E

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Jesse Costello-Good]

The value of the following should be 3, but on Safari it is 2.9999999999999996

Math.LOG10E * Math.log(1000)

This may be because Math.LOG10E is calculated too accurately. It is 0.43429448190325176 on Safari and 0.4342944819032518 on Firefox and IE.

One work around is to set the value of LOG10E to 0.4342944819032518. The following evaluates to 3 on Safari:

0.4342944819032518 * Math.log(1000)

This may affect other Math constants. LOG10E is the only one that I have checked.

[Timothy P. Horton]

I don't think this is actually a calculation problem, nor a problem with the constant.

Floating point representations are fundamentally flawed - not all numbers can be represented, and you will /quite/ often get strange errors like the one you described, even with very simple tests.

All numbers in JavaScriptCore (as far as I know) are represented internally as double-precision floating point numbers, thus everything is susceptible to this problem.

Take a peek:

http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems

or, if you're really interested:

http://docs.sun.com/source/806-3568/ncg_goldberg.html

But I might be wrong. The fact that the constant is different than in FF/IE is strange, though. Actually, Mathematica agrees with FF/IE (in that LOG10E should be ~0.4342944819032518276511)... so maybe it /is/ a bug!

[David Kilzer (:ddkilzer)]

Wolfram Alpha says it's 3.000000000000000000000000000000...

<http://www.wolframalpha.com/input/?i=Log10%5BE%5D+Log%5B1000%5D>

I still think Tibco should be rounding the result, though.

[Sam Weinig]

This was fixed in http://trac.webkit.org/changeset/79246.