function diff_bisect_(text1, text2) {
  // Cache the text lengths to prevent multiple calls.
  var text1_length = text1.length;
  var text2_length = text2.length;
  var max_d = Math.ceil((text1_length + text2_length) / 2);
  var v_offset = max_d;
  var v_length = 2 * max_d;
  var v1 = new Array(v_length);
  var v2 = new Array(v_length);
  // Setting all elements to -1 is faster in Chrome & Firefox than mixing
  // integers and undefined.
  for (var x = 0; x < v_length; x++) {
    v1[x] = -1;
    v2[x] = -1;
  }
  v1[v_offset + 1] = 0;
  v2[v_offset + 1] = 0;
  var delta = text1_length - text2_length;
  // If the total number of characters is odd, then the front path will collide
  // with the reverse path.
  var front = (delta % 2 != 0);
  // Offsets for start and end of k loop.
  // Prevents mapping of space beyond the grid.
  var k1start = 0;
  var k1end = 0;
  var k2start = 0;
  var k2end = 0;
  for (var d = 0; d < max_d; d++) {
    // Walk the front path one step.
    for (var k1 = -d + k1start; k1 <= d - k1end; k1 += 2) {
      var k1_offset = v_offset + k1;
      var x1;
      if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
        x1 = v1[k1_offset + 1];
      } else {
        x1 = v1[k1_offset - 1] + 1;
      }
      var y1 = x1 - k1;
      while (x1 < text1_length && y1 < text2_length &&
             text1.charAt(x1) == text2.charAt(y1)) {
        x1++;
        y1++;
      }
      v1[k1_offset] = x1;
      if (x1 > text1_length) {
        // Ran off the right of the graph.
        k1end += 2;
      } else if (y1 > text2_length) {
        // Ran off the bottom of the graph.
        k1start += 2;
      } else if (front) {
        var k2_offset = v_offset + delta - k1;
        if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
          // Mirror x2 onto top-left coordinate system.
          var x2 = text1_length - v2[k2_offset];
          if (x1 >= x2) {
            // Overlap detected.
            return diff_bisectSplit_(text1, text2, x1, y1);
          }
        }
      }
    }

    // Walk the reverse path one step.
    for (var k2 = -d + k2start; k2 <= d - k2end; k2 += 2) {
      var k2_offset = v_offset + k2;
      var x2;
      if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
        x2 = v2[k2_offset + 1];
      } else {
        x2 = v2[k2_offset - 1] + 1;
      }
      var y2 = x2 - k2;
      while (x2 < text1_length && y2 < text2_length &&
             text1.charAt(text1_length - x2 - 1) ==
             text2.charAt(text2_length - y2 - 1)) {
        x2++;
        y2++;
      }
      v2[k2_offset] = x2;
      if (x2 > text1_length) {
        // Ran off the left of the graph.
        k2end += 2;
      } else if (y2 > text2_length) {
        // Ran off the top of the graph.
        k2start += 2;
      } else if (!front) {
        var k1_offset = v_offset + delta - k2;
        if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
          var x1 = v1[k1_offset];
          var y1 = v_offset + x1 - k1_offset;
          // Mirror x2 onto top-left coordinate system.
          x2 = text1_length - x2;
          if (x1 >= x2) {
            // Overlap detected.
            return diff_bisectSplit_(text1, text2, x1, y1);
          }
        }
      }
    }
  }
  // Diff took too long and hit the deadline or
  // number of diffs equals number of characters, no commonality at all.
  return [[DIFF_DELETE, text1], [DIFF_INSERT, text2]];
}
Find the 'middle snake' of a diff, split the problem in two
and return the recursively constructed diff.
See Myers 1986 paper: An O(ND) Difference Algorithm and Its Variations.
@param {string} text1 Old string to be diffed.
@param {string} text2 New string to be diffed.
@return {Array} Array of diff tuples.
@private