## digitalmars.D.learn - about float & double

- spir <denis.spir gmail.com> Jan 18 2011
- =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> Jan 18 2011
- bearophile <bearophileHUGS lycos.com> Jan 19 2011
- dennis luehring <dl.soluz gmx.net> Jan 19 2011

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^(m-1) .. 2^⁽m-1)-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

Jan 18 2011

spir wrote:Is there somewhere a (clear) doc about float/double internals?

A very good read is: http://digitalmars.com/d/2.0/d-floating-point.htmlSome 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_floating-point_format http://en.wikipedia.org/wiki/Double_precision_floating-point_formatWhat 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

Jan 18 2011

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

Jan 19 2011

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^(m-1) .. 2^â�œm-1)-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

Jan 19 2011