sinPi function

double sinPi(double x)

Implementation

double sinPi(double x) {
  final double Two52 = 4.5036e+15; // 0x4330000000000000 ~4.5036e+15
  final double Two53 = 9.0072e+15; // 0x4340000000000000 ~9.0072e+15

  if (x < 0.25) {
    return -math.sin(math.pi * x);
  }

// argument reduction
  double z = x.floorToDouble();
  int n = 0;
  if (z != x) {
    // inexact
    x = x.remainder(2);
    n = (x * 4).toInt();
  } else {
    if (x >= Two53) {
      // x must be even
      x = 0.0;
      n = 0;
    } else {
      if (x < Two52) {
        z = x + Two52; // exact
      }
      n = Double.bit0(z);
      x = n.toDouble();
      n <<= 2;
    }
  }
  switch (n) {
    case 0:
      x = math.sin(math.pi * x);
      break;
    case 1:
    case 2:
      x = math.cos(math.pi * (0.5 - x));
      break;
    case 3:
    case 4:
      x = math.sin(math.pi * (1 - x));
      break;
    case 5:
    case 6:
      x = -math.cos(math.pi * (x - 1.5));
      break;
    default:
      x = math.sin(math.pi * (x - 2));
      break;
  }
  return -x;
}