Most efficient way to calculate hamming distance in ruby?

Question

In ruby, what is the most efficient way to calculate the bit difference between two unsigned integers (e.g. the hamming distance)?

Eg, I have integer a = 2323409845

Answer 1

Per the suggestion of mu is too short, I wrote a simple C extension to use __builtin_popcount , and using benchmark verified that it is at least 3X faster than ruby's optimized string functions..

I looked at the following two tutorials:

• Extending Ruby With C
• Ruby Extension in C in 5 min

In my program:

require './FastPopcount/fastpopcount.so'
include FastPopcount

def hamming(a,b)
  popcount(a^b)
end

Then in the dir containing my program, I create a folder "PopCount" with the following files.

extconf.rb:

# Loads mkmf which is used to make makefiles for Ruby extensions
require 'mkmf'

# Give it a name
extension_name = 'fastpopcount'

# The destination
dir_config(extension_name)

# Do the work
create_makefile(extension_name)

popcount.c:

// Include the Ruby headers and goodies
#include "ruby.h"

// Defining a space for information and references about the module to be stored internally
VALUE FastPopcount = Qnil;

// Prototype for the initialization method - Ruby calls this, not you
void Init_fastpopcount();

// Prototype for our method 'popcount' - methods are prefixed by 'method_' here
VALUE method_popcount(int argc, VALUE *argv, VALUE self);

// The initialization method for this module
void Init_fastpopcount() {
    FastPopcount = rb_define_module("FastPopcount");
    rb_define_method(FastPopcount, "popcount", method_popcount, 1); 
}

// Our 'popcount' method.. it uses the builtin popcount
VALUE method_popcount(int argc, VALUE *argv, VALUE self) {
    return INT2NUM(__builtin_popcount(NUM2UINT(argv)));
}

Then in the popcount directory run:

ruby extconf.rb make

Then run the program, and there you have it....fastest way to do hamming distance in ruby.