bswap.rb

#!/usr/bin/env ruby

data = []
File.open(ARGV[0]).each_byte {|b| data.push(b) }

(0..(data.size - 1)).step(4) {|i|
    x0 = data[i + 0]
    x1 = data[i + 1]
    x2 = data[i + 2]
    x3 = data[i + 3]
    STDOUT.write([x3, x2, x1, x0].pack('c*'))
}