CustomFloat

[Andrei Alexandrescu]

I found myself in need for smaller and specialized floating point types, 
where I configure the exact configuration (sign, mantissa, exponent, 
bias). See http://en.wikipedia.org/wiki/Half_precision for a half 
precision number slated for inclusion in IEEE 754r.

Would it be interesting to add a CustomFloat template to phobos? I'm 
thinking along the lines of:

template CustomFloat!(bool sign, uint mantissa,
         uint exponent, uint bias)
{
     ...
}

So half-precision numbers are:

alias CustomFloat!(true, 5, 10, 15) HalfFloat;

There are quite a few details to kink out but this is definitely doable. 
Numbers like 24-bit floating point and even 8-bit floating point would 
be easy to support too. For now CustomFloat would be intended 
exclusively as a compact storage mechanism; only conversion to the 
standard floating points would be implemented. Later, maybe we can get 
to implement some operations natively at least on machines that support 
them in hardware. I wanted to gauge interest in the topic.


Andrei