Re: [boost] [Boost.FixedPoint] Choose notation

Subject: Re: [boost] [Boost.FixedPoint] Choose notation
From: Dmitriy Gorbel (dmitriycpp_at_[hidden])
Date: 2013-04-29 11:51:04

 Michael Marcin-3 wrote
> I dislike the names. I don't really understand what the first 2 types
> have to do with fixed-point math, other than maybe as an implementation
> detail or degenerate fixed-point type (0 fractional bits). 

I add cardinal and integral types to the proposal because
this types required by C++1y proposal. I agree, this types
quite illogical. Maybe, this types proposed for supporting big integers, 
but I think for big integers better use Boost.Multiprecision library.

It's easy to implement integral types based on fractional, 
using template aliases, for example:
template<size_t Range> using cardinal = nonnegative<Range, 0>;
template<size_t Range> using integral = negatable<Range, 0>;

What community think about this?
Should library support integral fixed point types?

Neal Becker wrote
> Thank you.  The last time we discussed this topic, the issue was not one
> of 
> notation, but of different semantics that were desired by different end
> users of 
> a fixedpoint type.
> 
> I think there were several areas of disagreement - but perhaps primary was 
> whether arithmetic operations would produce different types or the same
> types, 
> and how to handle arithmetic between mixed types.  For example, does 
> multiplication of 2 8-bit quantities promote to 16 bits or not.
> 
> My preference is/was that no implicit conversion was ever performed and
> that it 
> always had to be explicit.  This is partly because the primary consumer
> for this 
> technology (I think) is those working on FPGA or ASIC hardware - and they
> should 
> always be aware of any such conversions.

Best way - conversion policy,
when user can choose between implicitly/explicitly conversion.
I will try to implement both variants. 

Sincerely,
Dmitriy. 

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