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

11 Apr 2012


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Vicente J. Botet Escriba wrote:
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Le 11/04/12 14:37, Neal Becker a écrit :
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* 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.
I want the library to avoid myself to apply these explicit operations. I 
don't  want to see on my code a shift to apply a round. IMO rounding 
should be applied when the resolution decreases during a conversion and
Le 12/04/12 00:25, Neal Becker a écrit :
the shift must depend on the difference and the rounding policy.
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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).
I don't understand. If the fixed_point type conveys the number of 
integer and fractional bits, why do you want to give them as parameters 
of the constructor?

Regards,
Vicente