Re: [boost] [fixed_point] Request for interest in a binary fixed point library

Subject: Re: [boost] [fixed_point] Request for interest in a binary fixed point library
From: Neal Becker (ndbecker2_at_[hidden])
Date: 2012-04-11 18:25:37

Vicente J. Botet Escriba wrote:

> Le 11/04/12 14:37, Neal Becker a écrit :
...
>> * fixed point<->  flt should be provided.  fixed.as_double() for example.
> Should the
> 
> fixed point ->  flt conversion take care of the rounding policy?
> 

In my prototype code, every time a right shift is used, rounding policy is 
applied.

rounding policy is a template parameter, with one default (the only one I care 
about).

The default is, 
template<typename base_type=int>
struct rnd {
  static base_type apply (base_type x, int frac_bits) {
    return ((x >> (frac_bits-1)) + 1) >> 1;
  }
};

To shift right by 'frac_bits' places, with rounding, we shift right 1 less 
place, add 1, then shift 1 more place.  When followed by saturation, this is the 
most common rounding operation I use for 2's complement hardware.

>> Also,
>> fixed (double, integer_bits, frac_bits) constructor, or something like it.
> Could you be more precise, please?

I want to be able to construct a fixed from a float, specifying the number of 
integer and fractional bits (or equivalent).