float128 are 16 bytes wide but have the structure of x87 80-bits + extra 6 bytes for alignment:
From "http://lwn.net/2001/features/OLS/pdf/pdf/x86-64.pdf": "... The x87 stack with 80-bit precision is only used for long double."
And:
e47 = float128(1e-47) e30 = float128(1e-30) e50 = float128(1e-50) (e30-e50) == e30 True (e30-e47) == e30 False
This shows that float128 has no more then 19 digits precision
Nadav.
-----הודעה מקורית-----
מאת: numpy-discussion-bounces@scipy.org בשם Robert Kern
נשלח: ג 09-דצמבר-08 22:40
אל: Discussion of Numerical Python
נושא: Re: [Numpy-discussion] Importance of order when summing values inanarray
On Tue, Dec 9, 2008 at 09:51, Nadav Horesh
As much as I know float128 are in fact 80 bits (64 mantissa + 16 exponent) so the precision is 18-19 digits (not 34)
float128 should be 128 bits wide. If it's not on your platform, please let us know as that is a bug in your build. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion