Webcam/include/engine/gpu/gpu_half_float.cpp

/* -----------------------------------------------------------------------------
	GSFramework
	Copyright 2001-2013 Emmanuel Julien. All Rights Reserved.
------------------------------------------------------------------------------*/


		#include "gpu/gpu_types.h"
		#include "gpu/gpu_renderer.h"

		using namespace GS::GPU;


//------------------------------------------------------------------------------
#ifdef	EGL_HALF_FLOAT_SUPPORT

// -15 stored using a single precision bias of 127
static	const unsigned int	HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP = 0x38000000;
// max exponent value in single precision that will be converted
// to Inf or Nan when stored as a half-float
static	const unsigned int	HALF_FLOAT_MAX_BIASED_EXP_AS_SINGLE_FP_EXP = 0x47800000;
// 255 is the max exponent biased value
static	const unsigned int	FLOAT_MAX_BIASED_EXP = (0xFF << 23);
static	const unsigned int	HALF_FLOAT_MAX_BIASED_EXP = (0x1F << 10);

hfloat				Types::FloatToHFloat(float f)
{
	unsigned int x = *(unsigned int *)&f;
	unsigned int sign = (unsigned short)(x >> 31);
	unsigned int mantissa;
	unsigned int exp;

	hfloat hf;

	// get mantissa
	mantissa = x & ((1 << 23) - 1);

	// get exponent bits
	exp = x & FLOAT_MAX_BIASED_EXP;

	if	(exp >= HALF_FLOAT_MAX_BIASED_EXP_AS_SINGLE_FP_EXP)
	{
		// check if the original single precision float number is a NaN
		if	(mantissa && (exp == FLOAT_MAX_BIASED_EXP))
		{
			// we have a single precision NaN
			mantissa = (1 << 23) - 1;
		}
		else
		{
			// 16-bit half-float representation stores number as Inf
			mantissa = 0;
		}

		hf = (((hfloat)sign) << 15) | (hfloat)(HALF_FLOAT_MAX_BIASED_EXP) | (hfloat)(mantissa >> 13);
	}
	// check if exponent is <= -15
	else	if	(exp <= HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP)
	{
		// store a denorm half-float value or zero.
		exp = (HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP - exp) >> 23;
		mantissa >>= (14 + exp);
		hf = (((hfloat)sign) << 15) | (hfloat)(mantissa);
	}
	else
		hf = (((hfloat)sign) << 15) | (hfloat)((exp - HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP) >> 13) | (hfloat)(mantissa >> 13);

	return hf;
}
float				Types::HFloatToFloat(hfloat hf)
{
	unsigned int sign = (unsigned int)(hf >> 15);
	unsigned int mantissa = (unsigned int)(hf & ((1 << 10) - 1));
	unsigned int exp = (unsigned int)(hf & HALF_FLOAT_MAX_BIASED_EXP);
	unsigned int f;

	if	(exp == HALF_FLOAT_MAX_BIASED_EXP)
	{
		// we have a half-float NaN or Inf
		// half-float NaNs will be converted to a single precision NaN
		// half-float Infs will be converted to a single precision Inf
		exp = FLOAT_MAX_BIASED_EXP;

		if	(mantissa)
			mantissa = (1 << 23) - 1;	// set all bits to indicate a NaN
	}
	else	if (exp == 0x0)
	{
		// convert half-float zero/denorm to single precision value
		if	(mantissa)
		{
			mantissa <<= 1;
			exp = HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;

			// check for leading 1 in denorm mantissa
			while ((mantissa & (1 << 10)) == 0)
			{
				// for every leading 0, decrement single precision exponent by 1
				// and shift half-float mantissa value to the left
				mantissa <<= 1;
				exp -= (1 << 23);
			}

			// clamp the mantissa to 10-bits
			mantissa &= ((1 << 10) - 1);
			// shift left to generate single-precision mantissa of 23-bits
			mantissa <<= 13;
		}
	}
	else
	{
		// shift left to generate single-precision mantissa of 23-bits
		mantissa <<= 13;

		// generate single precision biased exponent value
		exp = (exp << 13) + HALF_FLOAT_MIN_BIASED_EXP_AS_SINGLE_FP_EXP;
	}

	f = (sign << 31) | exp | mantissa;
	return *((float *)&f);
}

#else	// No half-float support.

hfloat		Types::FloatToHFloat(float f)		{	return f;	}
float		Types::HFloatToFloat(hfloat hf)		{	return hf;	}

#endif
//------------------------------------------------------------------------------