Unreadable Array inversion counter!

array_inversion.js

/*
 * Count inversions in an array using JavaScript
 * Friday fun writing algorithms as UNREADABLE CODE WITH FEW LINEZ FTW :D::D
 */

var array_inversions = function (A) {
  var I = 0, 
      R = function (A) { return (A.length < 2) ? A : M(R(A.splice(0, A.length/2)), R(A)) },
      M = function (B, C) {
        var D = []    
        while (B.length && C.length) {
            if (B[0] <= C[0]) D.push(B.shift())
            else {
              D.push(C.shift())
              I += B.length
            }
        }
        return B.length ? D.concat(B) : D.concat(C)
      }
  return R(A) ? I : null
}

console.log(array_inversions([1,3,5,2,4,6])) // 3
console.log(array_inversions([1,5,3,2,4,6])) // 4
console.log(array_inversions([6,5,4,3,2,1])) // 15