[Numpy-discussion] float96 on windows32 is float64?

Matthew Brett matthew.brett@gmail....
Thu Mar 15 23:10:03 CDT 2012


Hi,

Am I right in thinking that float96 on windows 32 bit is a float64
padded to 96 bits?  If so, is it useful?  Has anyone got a windows64
box to check float128 ?

Python 2.7.1 (r271:86832, Nov 27 2010, 18:30:46) [MSC v.1500 32 bit
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy as np
>>> np.__version__
'1.6.1'
>>> info = np.finfo(np.float96)
>>> print info
Machine parameters for float96
---------------------------------------------------------------------
precision= 15   resolution= 1e-15
machep=   -52   eps=        2.22044604925e-16
negep =   -53   epsneg=     1.11022302463e-16
minexp=-16382   tiny=       0.0
maxexp= 16384   max=        1.#INF
nexp  =    15   min=        -max
---------------------------------------------------------------------

>>> info.nmant
52

Confirming 52 (+1 implicit) significand digits

>>> np.float96(2**52)+1
4503599627370497.0
>>> np.float96(2**53)+1
9007199254740992.0

float96 claims 15 exponent digits (nexp above), but in fact it appears
to have 11, as does float64

>>> np.float64(2**1022) * 2
8.9884656743115795e+307
>>> np.float64(2**1022) * 4
__main__:1: RuntimeWarning: overflow encountered in double_scalars
inf
>>> np.float96(2**1022) * 2
8.9884656743115795e+307
>>> np.float96(2**1022) * 4
1.#INF

It does take up 12 bytes (96 bits)

>>> np.dtype(np.float96).itemsize
12

Thanks,

Matthew


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