On Sun, Nov 13, 2011 at 12:57 AM, Matthew Brett <matthew.br...@gmail.com>wrote:
> Hi, > > On Sat, Nov 12, 2011 at 11:35 PM, Matthew Brett <matthew.br...@gmail.com> > wrote: > > Hi, > > > > Sorry for my continued confusion here. This is numpy 1.6.1 on windows > > XP 32 bit. > > > > In [2]: np.finfo(np.float96).nmant > > Out[2]: 52 > > > > In [3]: np.finfo(np.float96).nexp > > Out[3]: 15 > > > > In [4]: np.finfo(np.float64).nmant > > Out[4]: 52 > > > > In [5]: np.finfo(np.float64).nexp > > Out[5]: 11 > > > > If there are 52 bits of precision, 2**53+1 should not be > > representable, and sure enough: > > > > In [6]: np.float96(2**53)+1 > > Out[6]: 9007199254740992.0 > > > > In [7]: np.float64(2**53)+1 > > Out[7]: 9007199254740992.0 > > > > If the nexp is right, the max should be higher for the float96 type: > > > > In [9]: np.finfo(np.float64).max > > Out[9]: 1.7976931348623157e+308 > > > > In [10]: np.finfo(np.float96).max > > Out[10]: 1.#INF > > > > I see that long double in C is 12 bytes wide, and double is the usual 8 > bytes. > > Sorry - sizeof(long double) is 12 using mingw. I see that long double > is the same as double in MS Visual C++. > > http://en.wikipedia.org/wiki/Long_double > > but, as expected from the name: > > In [11]: np.dtype(np.float96).itemsize > Out[11]: 12 > > Hmm, good point. There should not be a float96 on Windows using the MSVC compiler, and the longdouble types 'gG' should return float64 and complex128 respectively. OTOH, I believe the mingw compiler has real float96 types but I wonder about library support. This is really a build issue and it would be good to have some feedback on what different platforms are doing so that we know if we are doing things right. Chuck
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