Why don't we switch to C like floating pointed arithmetic instead of automatic expansion to reals?

[Fool via Digitalmars-d]

On Thursday, 4 August 2016 at 18:53:23 UTC, Walter Bright wrote:
> It has been proposed many times that the solution for D is to 
> have a function called toFloat() or something like that in 
> core.math, which guarantees a round to float precision for its 
> argument. But so far nobody has written such a function.

How can we ensure that toFloat(toFloat(x) + toFloat(y)) does not 
involve double-rounding?