Microbenchmark for integer power of floating point numbers in Ruby

What is this?

After reading Ruby 3.0 makes x ** 2 faster, I wanted to microbenchmark, so I microbenchmarked.

It doesn't stand from the viewpoint of practicality.

What to measure

ruby is 2.7.2 and 3.0.0-preview1. The environment is macOS Catalina 10.15.6. 2.2 GHz quad core Intel Core i7.

What to measure

For example, suppose you want to calculate the 11th power of x. There are the following methods.

name Method of calculation
x**n x**11
x*x*...*x x*x*x*x*x*x*x*x*x*x*x
use variables z=x*x;y=x*z*z;x*y*y
use '**2' ((x**2)**2*x)**2*x

The first two are good. ʻUse variables makes a decent amount of effort to reduce the number of multiplications. I didn't make every effort to reduce it, so for example, in the case of 27, " z = x * x * x; y = z * z; z = x * y * y; x * z * z "7 times It has become. If I try my best, it will probably be " z = x * x * x; y = z * z * z; y * y * y` "6 times, but I skipped it.

The last one is calculated using a lot of ** 2.

x is set to 3.0. I tried the index from 2 to 32. If the exponent value is small, x ** n and ʻuse'** 2' are the same, and x * x * ... * x and ʻuse variables are also the same.


All the graphs are Iteration per second, so the top is fast. Note the semi-log graph.


ʻUse variables seems to be fast up to the 10th power. Up to about 16th power, ʻuse variables and x ** n are pulled out. More than that, x ** n is faster.

Looking at the graph, it seems better to treat up to x ** 3 or x ** 4 specially, but what about it?


If you look at x ** n, you can see that 3.0.0-preview1 treats ** 2 specially.

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