How to simulate C style integer division?

[Steven D'Aprano]

On Fri, 22 Jan 2016 12:59 pm, Grobu wrote:

> On 21/01/16 09:39, Shiyao Ma wrote:
>> Hi,
>>
>> I wanna simulate C style integer division in Python3.
>>
>> So far what I've got is:
>> # a, b = 3, 4
>>
>> import math
>> result = float(a) / b
>> if result > 0:
>>    result = math.floor(result)
>> else:
>>    result = math.ceil(result)
>>
>>
>> I found it's too laborious. Any quick way?
>>
> 
> math.trunc( float(a) / b )


That fails for sufficiently big numbers:


py> a = 3**1000 * 2
py> b = 3**1000
py> float(a)/b  # Exact answer should be 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OverflowError: long int too large to convert to float


Note that Python gets the integer division correct:

py> a//b
2L


And even gets true division correct:

py> from __future__ import division
py> a/b
2.0


so it's just the intermediate conversion to float that fails.



-- 
Steven