[racket-dev] flonum vs. inexact-real

Is there any value to, on a 64 bit machine, having 32 bit floats be
immediate values to avoid boxing?

Robby

On Saturday, October 2, 2010, Matthew Flatt <mflatt at cs.utah.edu> wrote:
> Currently, every inexact real in Racket is represented by a 64-bit IEEE
> floating-point number.
>
> There's an `--enable-float' configuration option that enables support
> in Racket for 32-bit floating-point numbers. The use I see for 32-bit
> arithmetic is to mimic some other program that uses 32-bit
> floating-point arithmetic. (That was the original motivation, where I
> was trying to perform Racket computations that mimicked C computations
> in the drawing toolbox. I later settled on the solution of changing the
> drawing toolbox to use `double' instead of `float' everywhere.) With
> the current memory manager, I don't think there's any potential space
> gain from using 32-bit floats instead of 64-bit floats. Is there any
> other reason to use 32-bit floating point?
>
> The `--enable-float' option doesn't build at the moment, but the
> immediate problems could be fixed easily. The bigger problem is the
> interaction of 32-bit numbers and flonum-specific operations. As a
> concept related to performance, we don't want "flonum" to include
> multiple representations. It would make sense, though, to say that
> "flonum" indicates a 64-bit floating-point number and is therefore more
> specific than "inexact real". We would have to add `flonum?' and change
> all guards on unsafe flonum-specific operations to use `flonum?'
> instead of `inexact-real?'. Also, the distinction between inexact reals
> and flonums would complicate Typed Racket's already-complex number
> tower.
>
> Is it worth the effort to clean up this corner of the number system and
> leave room for 32-bit floating-point (and maybe other representations
> some day, as unlikely as that seems)? Or should we just declare
> "inexact real" and "flonum" to be always 64-bit floating point once and
> for all?
>
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