Strange result with timeit execution time measurment

[Peter Pearson]

On Sat, 15 Nov 2014 18:07:30 +0100, ast wrote:
>
> I needed a function f(x) which looks like sinus(2pi.x) but faster.
> I wrote this one:
>
> --------------------------
> from math import floor
>
> def sinusLite(x):
>     x = x - floor(x)
>     return -16*(x-0.25)**2 + 1 if x < 0.5 else 16*(x-0.75)**2 - 1
> --------------------------
>
> then i used module timeit to compare its execution time with math.sin()
> I put the sinusLite() function in a module named test.
>
> then:
>
>>>> import timeit
>>>> t1 = timeit.Timer("y=test.sinusLite(0.7)", "import test")
>>>> t2 = timeit.Timer("y=math.sin(4.39)", "import math")   ## 4.39 = 2*pi*0.7
>
>>>>  t1.repeat(3, 1000000)
> [1.9994622221539373, 1.9020670224846867, 1.9191573230675942]
>
>>>> t2.repeat(3, 1000000)
> [0.2913627989031511, 0.2755561810230347, 0.2755186762562971]
>
> so the genuine sinus is much faster than my so simple sinLite() !
> Amazing isnt it ? Do you have an explanation ?

I suppose math.sin is implemented in C.  Compiled languages (like C) are
much faster than interpreted languages like Python.

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