Tool Native Library Generator (C/C++ to B4A)

//LibFastMath 1.00 - Native Library Example

//FastSin() and FastCos() by Allen Chou
//http://allenchou.net/2014/02/game-math-faster-sine-cosine-with-polynomial-curves

//FastSqrt() adapted from Quake 3's Fast Inverse Square Root algorithm
//https://en.wikipedia.org/wiki/Fast_inverse_square_root

#define PI         (3.1415926535f)
#define HALF_PI    (0.5f * PI)
#define TWO_PI     (2.0f * PI)
#define TWO_PI_INV (1.0f / TWO_PI)

float FastSin(float x);
float FastCos(float x);
float FastSqrt(float x);

inline float Hill(float x)
{
  const float a0 = 1.0f;
  const float a2 = 2.0f / PI - 12.0f / (PI * PI);
  const float a3 = 16.0f / (PI * PI * PI) - 4.0f / (PI * PI);
  const float xx = x * x;
  const float xxx = xx * x;

  return a0 + a2 * xx + a3 * xxx;
}

float FastSin(float x)
{
  // wrap x within [0, TWO_PI)
  const float a = x * TWO_PI_INV;
  x -= static_cast<int>(a) * TWO_PI;
  if (x < 0.0f)
    x += TWO_PI;

  // 4 pieces of hills
  if (x < HALF_PI)
    return Hill(HALF_PI - x);
  else if (x < PI)
    return Hill(x - HALF_PI);
  else if (x < 3.0f * HALF_PI)
    return -Hill(3.0f * HALF_PI - x);
  else
    return -Hill(x - 3.0f * HALF_PI);
}

float FastCos(float x)
{
  return FastSin(x + HALF_PI);
}

float FastSqrt(float x)
{
    //This is the method used in Quake3
    const float xhalf = 0.5f*x;

    //Get bits for floating value
    union
    {
        float x;
        int i;
    } u;
    u.x = x;

    //Give initial guess y0
    u.i = 0x5f3759df - (u.i >> 1);

    //Newton step, repeating increases accuracy
    return (x*u.x*(1.5f - xhalf*u.x*u.x));
}