From: Petr Kovar <pejuko@...>
Date: 2011-08-18T05:55:16+09:00
Subject: Strangely slow float to int and int to float conversion

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Hi,

I had feeling that ruby arrays are very slow after I'd run some simple
float operations on array containing only integers.
But after I've writen some tests it turns out that the problem is
probably in conversion int to float or float to int.

Strange behaviour 1)

3_000_000 times simple int to float conversion is more then 10 times
slower than float to int
float to int...0.404731428s
int to float...4.803439434s

30_000_000 times int to float is 100 times slower than float to int
float to int...4.057228206
int to float...405.354131022

so 10 times more operations but it's 100 times slower!


Strange behaviour 2)

with operation multiply it flips:

operation (i * 0.3452523523).to_i is 5 times slower than i * 0.3452523523
(i * 0.3452523523).to_i ... 5.187890146
i * 0.3452523523 ... 1.054155473

and with 30_000_000 cycles it's 40 times slower
(i * 0.3452523523).to_i ... 413.333509812
i * 0.3452523523 ... 9.762297816

(i is integer)

so there the float result conversion to int is now as slow as int to
float in case 1.


I'm confused about this. Could you someone explain me how the
conversion works in ruby and how it is possible?
The test script is attached.

Thanks!

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Petr Kovar

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