On 13/08/2013 13:42, Chris Angelico wrote:
On Tue, Aug 13, 2013 at 1:12 PM, Anthony Papillion <papill...@gmail.com> wrote:
So I'm using the function below to test a large (617 digit) number for
primality. For some reason, when I execute the code, I get an error
telling me:
OverflowError: long int too large to convert to float
The error is being thrown on this line:
for x in range(3, int(n**0.5)+1, 2):
Python's integers are unbounded, storing arbitrary precision. Python's
floats are limited to the range of the underlying IEEE implementation.
You'll have a certain cutoff above which your system bombs.
float(1<<1023)
8.98846567431158e+307
float(1<<1024)
Traceback (most recent call last):
File "<pyshell#68>", line 1, in <module>
float(1<<1024)
OverflowError: long int too large to convert to float
(The exact cutoff may depend on how your Python is built, I think;
that was running on a 32-bit Python on Windows.)
[snip]
Here's a way to calculate the integer square root:
def int_sqrt(number):
root = 1
while True:
new_root = (root + number // root) // 2
if new_root == root:
break
root = new_root
return root
It's result is the largest integer whose square doesn't exceed the
original number.
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