Search code examples
pythonfloating-pointmodulo

Check if Large Float is Even or Odd

I have tried using the modulo operator for small floats and it works perfectly fine. For example: 5 % 2 returns 1.

But for other large floats that are read as exponential in python it just returns 0 every time even if the number is odd. Like this:

295147905179352825855 % 2 returns 0 even though that number is clearly odd.

Is there anything I can do to check large floats without python reading it as exponential?

Solution

  • What you said is not true. 295147905179352825855 % 2 should work because Python does arbitrary precision math on integers. There's no floating-point values in your question

    OTOH if you use a float like 295147905179352825855.0 then it obviously won't work because on most modern platforms Python uses IEEE-754 binary64 format which has only 53 bits of precision and can't store values such as 295147905179352825855.0. The closest value is 295147905179352825856.0 which is clearly an even number

    >>> 295147905179352825855 % 2
1
>>> 295147905179352825855.0 % 2
0.0
>>> format(295147905179352825855.0, '.20f')
'295147905179352825856.00000000000000000000'
>>> 295147905179352825856.0 == 295147905179352825855.0
True