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From: =?iso-8859-1?b?RnLpZOlyaWM=?= Praca <frederic.praca@free.fr>
Subject: Re: Representation clauses and side-efects on STM32F411 ravenscar
 runtime
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Date: 02 Aug 2015 20:27:51 GMT
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Date: 2015-08-02T22:27:51+02:00
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Le Sun, 02 Aug 2015 16:13:52 -0400, Bob Duff a écrit :

> Frédéric Praca <frederic.praca@free.fr> writes:
> 
>> Le Sun, 02 Aug 2015 15:54:50 -0400, Bob Duff a écrit :
>>
>>> "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:
>>> 
>>>> On 08/02/2015 01:59 AM, Frédéric Praca wrote:
>>>>> 
>>>>>    type Mantissa is range 0 .. 2**12 - 1 with Size => 12;
>>>>>    type Fraction is range 0 .. 2**4 - 1 with Size => 4;
>>> 
>>> Note that the Sizes will be 12 and 4 by default.
>>> 
>>>> Wouldn't modular types be better for these?
>>> 
>>> Why would you want wraparound arithmetic for these?  Seems like it
>>> would just hide bugs.
>>
>> I fully agree. Mantissa and Fraction don't have to use wraparound
>> arithmetic. In fact, these two variables together represent a fixed
>> point type and the magic must be inside the functions which calculates
>> these variables according to the bus frequency and by the way must take
>> care of the carry and possible overflow.
> 
> Then would a fixed-point type work?
> 
>     type Baud_Rate is delta 1.0/16 range ...;
>     for Baud_Rate'Small use 1.0/16;
Maybe. I have to try this but this is tightly coupled to my example and 
don't explain the side effects I also have on other records with 
representation clauses :)
Anyway, it could be a better way to represent things I need to 
investigate.

> - Bob
Fred