float equality

[bearophile]

Walter:

> There's a total lack of evidence for that.

MISRA-C standard disallows the equality among FP values. I presume they have some serious evidence for their choices, but I don't know such evidence. Today MISRA-C is one of the most serious attempts at fixing the holes in C language to write more reliable code for the industry. MISRA-C standard is sometimes extreme and I don't suggest to follow everything they say, but I suggest to not totally ignore what it says about many C features.


> 1. Roundoff error is not of a fixed magnitude.

I meant to replace the nude FP equality with a function that has the shared number of mantissa bits as third required argument. And then perform the normal FP equality using the "is" operator.

Regarding FP rounding errors, eventually it will be good to add to Phobos2 a library for Interval FP arithmetic, with trigonometric functions too, etc:
http://en.wikipedia.org/wiki/Interval_arithmetic

Bye,
bearophile