Re: float with 24-bit resolution

[Adrian Hoe <mailbox@nospam.adrianhoe.com.my>]

Adrian Hoe wrote:
> Jeffrey Creem wrote:
> 
>> <mailbox@adrianhoe.nospam.com.my> wrote in message
>> news:3F3CCB0F.543478AF@adrianhoe.nospam.com.my...
>>
>>> Hi,
>>>
>>> I looked through the LRM and searched CLA but I could not find any
>>> solution. Perhaps I've overlook somewhere.
>>>
>>> I need a float with 24-bit resolution. My data needs to be encoded into
>>> 24 bits at a scaling of 720 degrees / 2^24 bits with the most
>>> significant bit being the sign bit. This results in a value that ranges
>>> from +359.9999571 degrees (0x7FFFFF) to -360.0000000 degrees (0x800000)
>>> at increments of approximately 4.291534424e-5 degrees per bit.
>>
>>
>>
>> This does not sound anything like a float at all. It sounds much more 
>> like a
>> typical implementation of a fixed point type. Something along the 
>> lines of
>>
>> package My_Pack is
>>
>> The_Delta : constant := 4.291534424e-5;
>>
>>   type Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type is 
>> delta
>> The_Delta range - 360.0 .. 359.9999571;
>>   for  
>> Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type'Small use
>> The_Delta;
>>   for Probably_Gonna_Work_But_Language_Lawyers_Will_Complain_Type'Size 
>> use
>> 24;
>>
>>
>> end My_Pack;
>>
>> There are all sorts of things you can get bitten by here...especially 
>> with
>> the 24 bit requirement but when looking for
>>
>> a specific representation the details can be tricky.
>>
>>
>>
>> What are you really trying to achieve at a higher level (e.g. talking to
>> some hardware, sending some message to a device, etc?)
>>
>>
>>
>>
> 
> 
> Consider I have another data type which is to be encoded into 24 bits at 
> a scaling of 3600 degrees/sec / 2^24 bits with the most significant bit 
> being the sign bit. This results in a value that ranges from 
> +1799.999785 degrees per second (0x7FFFFF) to -1800.000 degrees per 
> second (0x800000) at increments of approximately 2.14576721e-4 degrees 
> per second per bit.
> 
> Can I declare just one 24-bit resolution float with a 24 bit storage 
> size for both problems? How?
> 
> Thanks.
> 
> -- 
> Adrian Hoe
> To email, remove "nospam" and "my"
> 


Sorry, I missed this.

Yes, I am trying to talk to some hardware.

--
Adrian Hoe
To email, remove "nospam" and "my"