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: Christopher Kormanyos (e_float_at_[hidden])
Date: 2012-04-11 17:21:01

>> 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 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.

> 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.

> Do you have any preferences for the namespace and class names?
Yes, in other post, "boost/fixed_point".

> Any comment is welcome.
I'll try on the weekend.

Best regards, Chris.