C++プログラミング日記

float wraparound( float Value, float Begin, float End )
{
	float dist = End - Begin;
	Value -= Begin;
	Value -= int( Value / dist ) * dist;
	long ofs = ( *(long*)&Value >> 31 ) & *(long*)&dist;
	return Value + *(float*)&ofs + Begin;
}

struct SINCOSCOEFFICIENT
{
	float	Value;
	float	Gradient;
};

SINCOSCOEFFICIENT	sincosLUT[ 0x100 ];
#define TWO_PI		6.2831853071795864

void init_sincosLUT( void )
{
	double t[ 0x100 ];
	for( int i = 0; i < 0x100; i++ )
		t[ i ] = sin( (double)i / 256 * TWO_PI );
	for( int i = 0; i < 0x100; i++ )
	{
		sincosLUT[ i ].Value    = (float)t[ i ];
		sincosLUT[ i ].Gradient = (float)( ( t[ ( i + 1 ) & 0xFF ] - t[ i ] ) / 65536 );
	}
}

inline float sinFast( float Angle )
{
	Angle /= TWO_PI;
	Angle -= (int)Angle;
	int index = int( Angle * 16777216.0f ) & 0x00FFFFFF;
	const SINCOSCOEFFICIENT& coef = sincosLUT[ index >> 16 ];
	return ( coef.Value + coef.Gradient * float( index & 0xFFFF ) );
}

inline float cosFast( float Angle )
{
	Angle /= TWO_PI;
	Angle -= (int)Angle;
	int index = int( Angle * 16777216.0f + 4194304.0f ) & 0x00FFFFFF;
	const SINCOSCOEFFICIENT& coef = sincosLUT[ index >> 16 ];
	return ( coef.Value + coef.Gradient * (float)( index & 0xFFFF ) );
}

inline void sincosFast( float Angle, float* pSin, float* pCos )
{
	Angle /= TWO_PI;
	Angle -= (int)Angle;
	int   index = int( Angle * 16777216.0f ) & 0x00FFFFFF;
	float delta = float( index & 0xFFFF );
	index >>= 16;
	const SINCOSCOEFFICIENT& sincoef = sincosLUT[ index ];
	const SINCOSCOEFFICIENT& coscoef = sincosLUT[ ( index + 0x40 ) & 0xFF ];
	*pSin = sincoef.Value + sincoef.Gradient * delta;
	*pCos = coscoef.Value + coscoef.Gradient * delta;
}

inline float modf( float X, float Y )
{
	return ( X - int( X / Y ) * Y );
}

#define PI	3.141592654f

struct vector3
{
	float	x;
	float	y;
	float	z;
};

void randUnitVector( vector3* pOut, random_generator & Rand )
{
	uint32_t value = Rand();
	uint32_t theta;
	float sin, cos;
	// pitch
	theta = ( value & 0xFFFF0000 );
	theta = ( theta >> 9 ) | ( theta >> 25 ) | 0x40000000;
	sincos( ( *(float*)&theta - 3.0f ) * PI, &sin, &cos );
	pOut->x = cos;
	pOut->y = cos;
	pOut->z = -sin;
	// yaw
	theta = ( value & 0x0000FFFF );
	theta = ( theta << 7 ) | ( theta >> 9 ) | 0x40000000;
	sincos( ( *(float*)&theta - 3.0f ) * PI, &sin, &cos );
	pOut->x *= cos;
	pOut->y *= sin;
}

inline void sincos( float Radian, float* pSin, float* pCos )
{
	float c, s;
	__asm
	{
		fld		Radian
		fsincos
		fstp	c
		fstp	s
	}
	*pSin = s;
	*pCos = c;
}