d3.svg.arc = function() {
  var innerRadius = d3_svg_arcInnerRadius,
      outerRadius = d3_svg_arcOuterRadius,
      startAngle = d3_svg_arcStartAngle,
      endAngle = d3_svg_arcEndAngle;

  function arc() {
    var r0 = innerRadius.apply(this, arguments),
        r1 = outerRadius.apply(this, arguments),
        a0 = startAngle.apply(this, arguments) + d3_svg_arcOffset,
        a1 = endAngle.apply(this, arguments) + d3_svg_arcOffset,
        da = (a1 < a0 && (da = a0, a0 = a1, a1 = da), a1 - a0),
        df = da < π ? "0" : "1",
        c0 = Math.cos(a0),
        s0 = Math.sin(a0),
        c1 = Math.cos(a1),
        s1 = Math.sin(a1);
    return da >= d3_svg_arcMax
      ? (r0
      ? "M0," + r1
      + "A" + r1 + "," + r1 + " 0 1,1 0," + (-r1)
      + "A" + r1 + "," + r1 + " 0 1,1 0," + r1
      + "M0," + r0
      + "A" + r0 + "," + r0 + " 0 1,0 0," + (-r0)
      + "A" + r0 + "," + r0 + " 0 1,0 0," + r0
      + "Z"
      : "M0," + r1
      + "A" + r1 + "," + r1 + " 0 1,1 0," + (-r1)
      + "A" + r1 + "," + r1 + " 0 1,1 0," + r1
      + "Z")
      : (r0
      ? "M" + r1 * c0 + "," + r1 * s0
      + "A" + r1 + "," + r1 + " 0 " + df + ",1 " + r1 * c1 + "," + r1 * s1
      + "L" + r0 * c1 + "," + r0 * s1
      + "A" + r0 + "," + r0 + " 0 " + df + ",0 " + r0 * c0 + "," + r0 * s0
      + "Z"
      : "M" + r1 * c0 + "," + r1 * s0
      + "A" + r1 + "," + r1 + " 0 " + df + ",1 " + r1 * c1 + "," + r1 * s1
      + "L0,0"
      + "Z");
  }

  arc.innerRadius = function(v) {
    if (!arguments.length) return innerRadius;
    innerRadius = d3_functor(v);
    return arc;
  };

  arc.outerRadius = function(v) {
    if (!arguments.length) return outerRadius;
    outerRadius = d3_functor(v);
    return arc;
  };

  arc.startAngle = function(v) {
    if (!arguments.length) return startAngle;
    startAngle = d3_functor(v);
    return arc;
  };

  arc.endAngle = function(v) {
    if (!arguments.length) return endAngle;
    endAngle = d3_functor(v);
    return arc;
  };

  arc.centroid = function() {
    var r = (innerRadius.apply(this, arguments)
        + outerRadius.apply(this, arguments)) / 2,
        a = (startAngle.apply(this, arguments)
        + endAngle.apply(this, arguments)) / 2 + d3_svg_arcOffset;
    return [Math.cos(a) * r, Math.sin(a) * r];
  };

  return arc;
};

var d3_svg_arcOffset = -π / 2,
    d3_svg_arcMax = 2 * π - 1e-6;

function d3_svg_arcInnerRadius(d) {
  return d.innerRadius;
}

function d3_svg_arcOuterRadius(d) {
  return d.outerRadius;
}

function d3_svg_arcStartAngle(d) {
  return d.startAngle;
}

function d3_svg_arcEndAngle(d) {
  return d.endAngle;
}
