[fpc-devel] real, float, double specs

[Ralf Quint]

On 2/11/2014 4:53 PM, Martin Frb wrote:
> I am trying to figure out the internal representation of these. (So 
> they can be converted, including conversion form sizes not present in fpc)
>
> They are all floating point? Pascal has no fixed point? (nevertheless, 
> rules for fixed point may also be of interest)
>
> dwarf2 says it is specified in each platforms ABI, but I have not 
> found that (not even found the ABI yet).
> Only found: 
> http://en.wikipedia.org/wiki/Computer_number_format#Representing_fractions_in_binary
>
> And http://www.freepascal.org/docs-html/ref/refsu6.html#x28-310003.1.2
>
>> Type 	Range 	Significant digits 	Size
>> ------------------------------------------------------------------------
>> 	
>> ------------------------------------------------------------------------
>> 	
>> ------------------------------------------------------------------------
>> 	
>> ------------------------------------------------------------------------
>> Real 	platform dependant 	??? 	4 or 8
>> Single 	1.5E-45 .. 3.4E38 	7-8 	4
>> Double 	5.0E-324 .. 1.7E308 	15-16 	8
>> Extended 	1.9E-4932 .. 1.1E4932 	19-20 	10
>> Comp 	-2E64+1 .. 2E63-1 	19-20 	8
>> Currency 	-922337203685477.5808 .. 922337203685477.5807 	19-20 	8
>>
> apparently there also is real46 (never heard of real16)
>
> The size will actually be in the dwarf, so that I got.
>
> But from that how do I know how many bits are in the exponent? (and 
> how many in the number). Apparently it depends on the CPU? But where 
> to get the info?
For all but Real48 (not Real46 or Real16), those are conformant with 
IEEE 754 (http://grouper.ieee.org/groups/754/)

Real48 is the non-IEEE754 (predating it) floating point format that was 
used in the early Borland Turbo Pascal...

Ralf


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