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[web] Is JavaScript floating-point math deterministic?

Started by Gamer Gamester Aug 30, 2011 at 6:45 AM 0 replies 2.8k views

Original Post

Aug 30, 2011 at 6:45 AM

Is JavaScript floating-point math deterministic across modern browsers and OSes?

I haven't been able to find much info on this... though I'm getting the impression that the answer is an unfortunate "no".

Hodgman

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Hodgman

Aug 30, 2011 at 7:21 AM

According to the spec, they seem to dictate compliance with IEEE 754, which should give the usual determinism caveats...

The Number type has ... values, representing the double precision 64-bit format IEEE 754 values as specified in the IEEE Standard for Binary Floating-Point Arithmetic...
This procedure corresponds exactly to the behaviour of the IEEE 754 ?"round to nearest" mode...
The result of a floating-point multiplication is governed by the rules of IEEE 754 binary double-precision arithmetic... The result of division is determined by the specification of IEEE 754 arithmetic...
etc...[/quote]...but, then again, when did browsers ever faithfully implement common specifications?
You can see the list of dialects and the version of the spec they purport to implement on wikipedia.

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