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module.exports = function(haystack, needle, comparator, low, high) {
  var mid, cmp;

  if(low === undefined)
    low = 0;

  else {
    low = low|0;
    if(low < 0 || low >= haystack.length)
      throw new RangeError("invalid lower bound");
  }

  if(high === undefined)
    high = haystack.length - 1;

  else {
    high = high|0;
    if(high < low || high >= haystack.length)
      throw new RangeError("invalid upper bound");
  }

  while(low <= high) {
    // The naive `low + high >>> 1` could fail for array lengths > 2**31
    // because `>>>` converts its operands to int32. `low + (high - low >>> 1)`
    // works for array lengths <= 2**32-1 which is also Javascript's max array
    // length.
    mid = low + ((high - low) >>> 1);
    cmp = +comparator(haystack[mid], needle, mid, haystack);

    // Too low.
    if(cmp < 0.0)
      low  = mid + 1;

    // Too high.
    else if(cmp > 0.0)
      high = mid - 1;

    // Key found.
    else
      return mid;
  }

  // Key not found.
  return ~low;
}