Re: [boost] Fixed point integer proposal

Subject: Re: [boost] Fixed point integer proposal
From: Neal Becker (ndbecker2_at_[hidden])
Date: 2009-06-25 09:57:33

Patrick Mihelich wrote:

> On Wed, Jun 24, 2009 at 12:51 PM, Soren Holstebroe
> <holstebroe_at_[hidden]>wrote:
> 
>> Would there be public interest in a template like that in the boost
>> library?
> 
> 
> Yes, very much so. My main use case is also image processing.
> 
> It would be useful if you could compare your work to other
> implementations, such as:
>  * Phil Endecott's related proposal last year, and the ensuing discussion:
> http://lists.boost.org/Archives/boost/2007/04/120082.php
>  * Dr. Dobbs, "Fixed-Point Arithmetic Types for C++,"
> http://www.ddj.com/cpp/184401992
> 
> How are multiplication and division handled?
> 
> Is overflow detection and/or saturation arithmetic supported?
> 
>
I have posted here before some code based on constrained_value.  One 
difficulty with this area is that users have different opinions on what the 
semantics should be.

For example, does a(24bit) x b(24bit) -> c(24bit), or c(48bit)?

My preference is to be explicit about these issues, meaning 24bit x 24bit -> 
24 bit.  If you want more, you cast the operands first.  Similarly there 
were some questions on division.

My implementation also uses boost::operators.  In addition, I have 2 
versions, one which the bit-widths are set at compile time, and the other 
set at runtime (I use the latter to expose to python).

Since it is small, I am attaching the runtime version