Re: [boost] Decimal floating point library

From: Stefan Slapeta (stefan_at_[hidden])
Date: 2006-03-02 08:34:12

Beman Dawes wrote:
> 
> Stefan (or others), would you have any interest in implementing this 
> proposal for Boost (under the Boost license)?

of course :-)

 >
 > Although it would be a big job, the critical interface design and
 > documentation work are essentially done in that you can just reference
 > Robert's paper.

I don't fully agree. Robert's paper (which is again based on the WG14 
library extension) specifies the interface for three IEEE conformant 
decimal types. The main intention of IEEE is to specify three decimal 
floating point types in order to be able to provide hardware support for 
these particular types later! Undoubtedly, this is welcome, but the 
story is over here.

The requirements of mathematics, especialy for large integer 
computation, are another side and go far beyond this scope!
What we need is:

(1) an arbitrary length integer type
(2) an arbitrary length decimal floating point type, which is a
     combination of (1) with an integer-like scale so that
     decimal_value = large_integer_value / 10 ^ scale
(3) three specializations of (2) to provide the IEEE and TR2
     conforming interface (32, 64, 128 digits)

IMO (1) and (2) should have a template parameter that specifies the 
number of digits. Furthermore, it *could* be possible that (3) are plain 
typedefs.

> 
> It would a useful library for Boost users, and any issues you ran into would 
> illuminate areas of Robert's proposal that needs more work. The resulting 
> improvements would be of long term benefit for C++.
> 

The usefulness is beyond any doubt.
I would enjoy working on a decimal library, but I can't do that on my 
own. It's simply too much for one...

Stefan