src/arrays/bisect.js

d3.bisector = function(f) {
  return {
    left: function(a, x, lo, hi) {
      if (arguments.length < 3) lo = 0;
      if (arguments.length < 4) hi = a.length;
      while (lo < hi) {
        var mid = lo + hi >>> 1;
        if (f.call(a, a[mid], mid) < x) lo = mid + 1;
        else hi = mid;
      }
      return lo;
    },
    right: function(a, x, lo, hi) {
      if (arguments.length < 3) lo = 0;
      if (arguments.length < 4) hi = a.length;
      while (lo < hi) {
        var mid = lo + hi >>> 1;
        if (x < f.call(a, a[mid], mid)) hi = mid;
        else lo = mid + 1;
      }
      return lo;
    }
  };
};

var d3_bisector = d3.bisector(function(d) { return d; });
d3.bisectLeft = d3_bisector.left;
d3.bisect = d3.bisectRight = d3_bisector.right;