Re: long double data type
Re: long double data type
- Subject: Re: long double data type
- From: Richard Dobson <email@hidden>
- Date: Tue, 15 Jun 2010 23:05:40 +0100
On 15/06/2010 22:42, Luigi Castelli wrote:
The fact that long double is 80 bits is an implementation detail,
not a predefined type. On PowerPC, long double = double unless you
force it to be bigger in which case it is emulated in software with
2 doubles (simplistic statement!).
Exactly. On my system, the size of a long double is 128 bits (16
bytes), not 80 bits. Why would it not be IEEE compliant?
there is a 128bit IEEE standard, summarised here:
http://en.wikipedia.org/wiki/Quadruple_precision_floating-point_format
Note that long double = 128bits is not universally supported yet, so
use of it is not as portable as you might wish. Also note it tends to
depend on software emulation, so if you ~can~ arrange your dsp to manage
with native 64bit types, it will clearly be advantageous to do so. There
will remain some curiosity on this list as to what you are doing for
which 64bits are insufficient.
The only explicit use of 80 bit floats I am aware of is, curiously
enough, in the AIFF spec where it is used, more than a little
extravagantly, for the sample rate.
Richard Dobson
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