Math float equivalence

Don Clugston dac at
Wed Jul 5 12:55:01 PDT 2006

Lucas Goss wrote:
> In many game libraries, they often have some type of float equivalence 
> function to work around rounding differences, something like:
> float equal(float f1, float f2, epsilon=1e-6)
> {
>   // check for equivalence between f1 and f2
>   // where the difference between them is less than epsilon
> }
> How does D check for equivalence between floats, does it account for 
> rounding errors? If not, is there a library function for this? I noticed 
> "math.feqrel" (I still loathe the names of all these functions, I have 
> no idea what feqrel is supposed to mean)

It stands for "relative floating point equality". If you have a better 
name, let me know (I wrote it).

 > but I would think it would take a lot more processing than to just check
 > equivalence.

Check the source in std.math. It's actually a very fast function (it 
only has a couple of subtractions and two predictable branches).
It's a comparison that exactly captures the precision of IEEE arithmetic.
In the Helix library on dsource is a version which is more applicable to 
  games, since it has an absolute difference as well.

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