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Subject: Re: [boost] [Boost.FixedPoint] Choose notation
From: Michael Marcin (mike.marcin_at_[hidden])
Date: 2013-04-29 03:26:01

On 4/29/2013 1:46 AM, Andrey Semashev wrote:
> On Mon, Apr 29, 2013 at 10:41 AM, Vicente J. Botet Escriba <
> vicente.botet_at_[hidden]> wrote:
>> BTW, the choice of the names in the C++1y proposal was a source of
>> conflicts (as always).
>> In my prototype I used
>> fxp_uint and fxp_int
>> fxp_ufract and fxp_fract
>> (fxp_ufreal and fxp_real)
>> Now if you put these classes on a specific namespace for each notation the
>> choice of the default can be deferred without a major impact on the plan.
>> namespace fixed_point {
>> namespace q { }
>> namespace cxx1y {}
>> // if the default is cxx1y notation (a better name is welcome, e.g. rr
>> for range and resolution)
>> using cxx1y::fxp_uint;
>> using cxx1y::fxp_int;
>> ...
>> }
>> With this approach the user could be precise enough
>> fixed_point::q::fxp_fract<8,4>**;
>> we could also name the namespace for fixed points fxp and use
>> fxp::q::fract<8,4>;
>> fxp::rr::uinteger<8,4>;
> Please, no cryptic abbreviations (and especially one letter names).

I've always felt that if floating point numbers are called float then
fixed point numbers should be called fixed.

fixed<24,8> representing a signed 24.8 fixed-point would be my preferred
naming convention.

It could be an alias for signed_fixed<24,8> much like int is for signed
int. Then naturally if you needed to support unsigned fixed point types
you could use unsigned_fixed<24,8>.

I could see an argument made for fixed<int32_t,4> specifying the storage
type and the radix, in this case 28.4. This handles the signed vs
unsigned naturally and doesn't allow you to have (in my view) strange
types like 8.4 which seems to require an odd 12bit integer type.

If you absolutely needed an 8.4 type then you need fixed-width integer
support beyond that provided by <cstdint>. You could provide an
implementation of integer<12> that is a 12 bit integer and then make
fixed<integer<12>,4>. In my opinion this is another library outside the
scope of a fixed-point library.

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