On Sat, Oct 29, 2011 at 8:49 PM, Matthew Brett <matthew.brett@gmail.com>wrote:
Hi,
On Sat, Oct 29, 2011 at 3:55 PM, Matthew Brett <matthew.brett@gmail.com> wrote:
Hi,
Can anyone think of a good way to set a float128 value to an arbitrarily large number?
As in
v = int_to_float128(some_value)
?
I'm trying things like
v = np.float128(2**64+2)
but, because (in other threads) the float128 seems to be going through float64 on assignment, this loses precision, so although 2**64+2 is representable in float128, in fact I get:
In [35]: np.float128(2**64+2) Out[35]: 18446744073709551616.0
In [36]: 2**64+2 Out[36]: 18446744073709551618L
So - can anyone think of another way to assign values to float128 that will keep the precision?
To answer my own question - I found an unpleasant way of doing this.
Basically it is this:
def int_to_float128(val): f64 = np.float64(val) res = val - int(f64) return np.float128(f64) + np.float128(res)
Used in various places here:
https://github.com/matthew-brett/nibabel/blob/e18e94c5b0f54775c46b1c690491b8...
Best,
It might be useful to look into mpmath. I didn't see any way to export mp values into long double, but they do offer a number of resources for working with arbitrary precision. We could maybe even borrow some of their stuff for parsing values from strings Chuck