Module: Suby::MovieHasher

Defined in:
lib/suby/movie_hasher.rb

Overview

from trac.opensubtitles.org/projects/opensubtitles/wiki/HashSourceCodes

Constant Summary collapse

CHUNK_SIZE =

in bytes

64 * 1024
MASK64 =

2^64 - 1

0xffffffffffffffff

Class Method Summary collapse

Class Method Details

.compute_hash(file) ⇒ Object 



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# File 'lib/suby/movie_hasher.rb', line 8

def self.compute_hash(file)
  filesize = file.size
  hash = filesize

  # Read 64 kbytes, divide up into 64 bits and add each
  # to hash. Do for beginning and end of file.
  file.open('rb') do |f|
    # Q = unsigned long long = 64 bit
    f.read(CHUNK_SIZE).unpack("Q*").each do |n|
      hash = (hash + n) & MASK64
    end

    f.seek([0, filesize - CHUNK_SIZE].max, IO::SEEK_SET)

    # And again for the end of the file
    f.read(CHUNK_SIZE).unpack("Q*").each do |n|
      hash = (hash + n) & MASK64
    end
  end

  "%016x" % hash
end