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Subject: Re: [boost] [fixed_point] Request for interest in a binary fixed point library
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-04-11 18:21:02

Le 11/04/12 23:21, Christopher Kormanyos a écrit :
>>> Yes! Absolutely interested!
>>> I use fixed-point extensively with hard real-time microcontroller systems.
>>> I am particularly interested in stuff like a 7.8 and 15.16 signed split.
>> What 7.8 stands for? 7 bits for the integer part and 8 for the fractional part?
> I use 7.8, for example, for a signed 16-bit type with one sign bit,
> seven mantissa binary digits and eight binary fractional digits.
I see so, it corresponds to the i_f format.
>> I guess you prefer a specific class for signed fixed_points and not a template parameter.
>> sfp<7,8>
>> versus
>> fp<int16_t, 7,8>
>> Do you mind if the library propose some meta-function to specify different formats, e.g.
>> format_i_f<7,8>::type and format_i_f<15,16>::type
>> An alternative design is to have a format parameter, so for example the user could use specific formats
> <snip>
>> where i_f has as parameters the number of integral and fractional bits and r_r
>> has as parameters the range and resolution. Currently my prototype and the C++
>> proposal uses this r_r format. Others use the total number of bits
>> (width including the sign) and the fractional w_f
> I can use anything. The great advantage of your selected
> convention is that it is absolutely clear how many digits
> there are in mantissa and fraction. I like it.
I will try introducing the format as a parameter on my prototype soon.
>> Do you mind if the rounding strategy is a template parameter?
>> An enumeration or and open policy?
> Do we even really need a rounding policy? I honestly don't know.
> I thought the whole deal with fixed-point was to free us from the
> burdens of formal floating-point representation and obtain efficiency
> and exactness via near-integer representation. Maybe others have a
> clear, or more formal, suggestion here.
Converting from fixed_point numbers with different resolution needs
rounding. Divide request also a resolution to which round.


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