Re: [boost] Fixed point integer proposal

Subject: Re: [boost] Fixed point integer proposal
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2009-06-25 15:19:59

Soren Holstebroe wrote:
> In my template N bit x N bit equals N bit per default.

Which of the 2N possible bits do you keep, and which do you discard?

I chose to try to behave as closely as possible to how built-in integer 
types work.  If I multiply uint8_t * uint8_t and assign the result to a 
uint32_t, it works.  IIUC the equivalent operation would not work with 
your implementation, right?

> The number one design criteria was speed. Why would you use fixed
> point instead of floats if not for speed?

In my case, it has been for two reasons:
- To store in 32 bits a value with a precision of 2^-32, not the 2^-24 
that you get with a float.
- To allow me to do Z-curve bit manipulations on the values.

Speed is also useful of course.

As I think you are already seeing from the other responses there are 
various different applications for fixed point.  Your choice is either 
to try to get a subset of the possible functionality that does what you 
want approved, or to invest some effort in expanding your library to 
make everyone happy.

Regards, Phil.