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 < Math.PI ? "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 = -Math.PI / 2,

    d3_svg_arcMax = 2 * Math.PI - 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;

}