Hi, On Wed, Feb 29, 2012 at 12:13 PM, Jonathan Rocher <jroc...@enthought.com> wrote: > Thanks to your question, I discovered that there is a float128 dtype in > numpy > > In[5]: np.__version__ > Out[5]: '1.6.1' > > In[6]: np.float128? > Type: type > Base Class: <type 'type'> > String Form:<type 'numpy.float128'> > Namespace: Interactive > File: > /Library/Frameworks/Python.framework/Versions/7.2/lib/python2.7/site-packages/numpy/__init__.py > Docstring: > 128-bit floating-point number. Character code: 'g'. C long float > compatible.
Right - but remember that numpy float128 is different on different platforms. In particular, float128 is any C longdouble type that needs 128 bits of memory, regardless of precision or implementation. See [1] for background on C longdouble type. The numpy platforms I know about are: Intel : 80 bit float padded to 128 bits [2] PPC : pair of float64 values [3] Debian IBM s390 : real quadruple precision [4] [5] I see that some Sun machines implement real quadruple precision in software but I haven't run numpy on a Sun machine [6] [1] http://en.wikipedia.org/wiki/Long_double [2] http://en.wikipedia.org/wiki/Extended_precision#x86_Architecture_Extended_Precision_Format [3] http://en.wikipedia.org/wiki/Double-double_%28arithmetic%29#Double-double_arithmetic [4] http://en.wikipedia.org/wiki/Double-double_%28arithmetic%29#IEEE_754_quadruple-precision_binary_floating-point_format:_binary128 [5] https://github.com/nipy/nibabel/issues/76 [6] http://en.wikipedia.org/wiki/Double-double_%28arithmetic%29#Implementations > Based on some reported issues, it seems like there are issues though with > this and its mapping to python long integer... > http://mail.scipy.org/pipermail/numpy-discussion/2011-October/058784.html I tried to summarize the problems I knew about here: http://mail.scipy.org/pipermail/numpy-discussion/2011-November/059087.html There are some routines to deal with some of the problems here: https://github.com/nipy/nibabel/blob/master/nibabel/casting.py After spending some time with the various longdoubles in numpy, I have learned to stare at my code for a long time considering how it might run into the various problems above. Best, Matthew _______________________________________________ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion