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Date: Fri, 15 Aug 2003 20:52:57 +0800
From: Adrian Hoe <mailbox@nospam.adrianhoe.com.my>
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Subject: Re: float with 24-bit resolution
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Date: 2003-08-15T20:52:57+08:00
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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
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