Tim Peters added the comment:
It sounds like you need to read an introduction (any!) to computer
floating-point formats. The relevant part in the output you showed is this:
mant_dig=53
As on almost other current machines, your platform's floating point format is
restricted to 53 bits of
Farhan Sajjad added the comment:
Maybe I need to go back and understand why this loss of precision is taking
place for the int->float conversion, and why for certain numbers.
Also, it does not work in Python 2. Please disregard the previous message.
--
resolution: -> not a bug
Farhan Sajjad added the comment:
Thanks for your input Tim. Here is what I understand:
1. In Python 3, int can be arbitrarily large.
2. C double data type can hold very large numbers, and the number tested here
is quite small compared to the max. It even fits fine in a long long int.
3. Quite
Tim Peters added the comment:
Note that this pure Python gives the same result:
>>> "%.0f" % float(1639873214337061279)
'1639873214337061376'
That's not surprising: int -> float conversion is limited to the precision of
a Python float, which is a C double, which is almost certainly just 53
New submission from Farhan Sajjad :
Found this rather obscure behavior where certain 64 bit numbers are changing
(probably losing precision somewhere down the call chain) if converted from
PyLong to double using the PyLong_AsDouble C API function.
TO REPRODUCE:
#define __SIZEOF_STRS__ 512
