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January 18, 2011 about float & double  

 
Hello, Is there somewhere a (clear) doc about float/double internals? Some more particuliar questions: What is the internal bit layout? (mantissa, sign, exponent) Can I assume the "integral range" is [2^(m1) .. 2^⁽m1)1], where m is the number of mantissa bits? What are the values used to represent thingies like NaNs, inf, error? (Or are there not represented as values?) How would you get a float's integral and fractional parts without performing arithmetic? (I think at bit ops, indeed) Denis _________________ vita es estrany spir.wikidot.com 
January 18, 2011 Re: about float & double  

 
Posted in reply to spir  spir wrote: > Is there somewhere a (clear) doc about float/double internals? A very good read is: http://digitalmars.com/d/2.0/dfloatingpoint.html > Some more particuliar questions: > > What is the internal bit layout? (mantissa, sign, exponent) IEEE floating point format. This page has links to different representations: http://en.wikipedia.org/wiki/Ieee_floating_point Specifically: http://en.wikipedia.org/wiki/Single_precision_floatingpoint_format http://en.wikipedia.org/wiki/Double_precision_floatingpoint_format > What are the values used to represent thingies like NaNs, inf, error? > (Or are there not represented as values?) They are available on the documents above. > How would you get a float's integral and fractional parts without > performing arithmetic? (I think at bit ops, indeed) Here is a function with endianness "issues" that I had used with different types: import std.stdio; void display_bytes(T)(ref T variable) { const ubyte * begin = cast(ubyte*)&variable; writefln("type : %s", T.stringof); writefln("value : %s", variable); writefln("address : %s", begin); writef( "representation: "); foreach (p; begin .. begin + T.sizeof) { writef("%02x ", *p); } writeln(); writeln(); } void main() { auto d_nan = double.nan; auto d_inf = double.infinity; display_bytes(d_nan); display_bytes(d_inf); } Ali 
January 19, 2011 Re: about float & double  

 
Posted in reply to spir  spir:
> Is there somewhere a (clear) doc about float/double internals?
> Some more particuliar questions:
>
> What is the internal bit layout? (mantissa, sign, exponent)
There is the real type too (>= 10 bytes).
Bye,
bearophile

January 19, 2011 Re: about float & double  

 
Posted in reply to spir  > Is there somewhere a (clear) doc about float/double internals? > Some more particuliar questions: > > What is the internal bit layout? (mantissa, sign, exponent) > > Can I assume the "integral range" is [2^(m1) .. 2^â�œm1)1], where m is > the number of mantissa bits? > > What are the values used to represent thingies like NaNs, inf, error? > (Or are there not represented as values?) > > How would you get a float's integral and fractional parts without > performing arithmetic? (I think at bit ops, indeed) Wikipedia is very informative and the phobos math implementation is a very good source for the bit ops stuff http://www.dsource.org/projects/phobos/browser/trunk/phobos/std/math.d 
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