Why is time difference on calculating this so big?

python

Solution

>>> import dis
>>> method1 = lambda: (127 / 60) * 60
>>> method2 = lambda: 127 - 127 % 60
>>> dis.dis(method1)
  1           0 LOAD_CONST               1 (127)
              3 LOAD_CONST               2 (60)
              6 BINARY_DIVIDE       
              7 LOAD_CONST               2 (60)
             10 BINARY_MULTIPLY     
             11 RETURN_VALUE        
>>> dis.dis(method2)
  1           0 LOAD_CONST               1 (127)
              3 LOAD_CONST               3 (7)
              6 BINARY_SUBTRACT     
              7 RETURN_VALUE

In the second case, the modulo operation is simply optimized away.

Problem

I need to round lots of UNIX timestamps down to their respective minutes (expressed as timestamp again). Out of pure curiosity I timed two methods: ``` %timeit (127/60)*60 10000000 loops, best of 3: 76.2 ns per loop %timeit 127 - 127%60 10000000 loops, best of 3: 34.1 ns per loop ``` I ran this several times and second method is consistently around twice as fast as first one. Why is the difference so big?

Original source