/**
 * Copyright (c) 2006-2016 LOVE Development Team
 *
 * This software is provided 'as-is', without any express or implied
 * warranty.  In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would be
 *    appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 **/

#include "halffloat.h"

namespace love
{

// Code from ftp://www.fox-toolkit.org/pub/fasthalffloatconversion.pdf

static bool initialized = false;

// tables for half -> float conversions
static uint32 mantissatable[2048];
static uint16 offsettable[64];
static uint32 exponenttable[64];

// tables for float -> half conversions
static uint16 basetable[512];
static uint8 shifttable[512];


static uint32 convertMantissa(uint32 i)
{
	uint32 m = i << 13; // Zero pad mantissa bits
	uint32 e = 0; // Zero exponent

	while (!(m & 0x00800000)) // While not normalized
	{
		e -= 0x00800000; // Decrement exponent (1<<23)
		m <<= 1; // Shift mantissa
	}

	m &= ~(0x00800000); // Clear leading 1 bit
	e += 0x38800000; // Adjust bias ((127-14)<<23)

	return m | e; // Return combined number
}

void halfInit()
{
	if (initialized)
		return;

	initialized = true;


	// tables for half -> float conversions.

	mantissatable[0] = 0;

	for (uint32 i = 1; i < 1024; i++)
		mantissatable[i] = convertMantissa(i);

	for (uint32 i = 1024; i < 2048; i++)
		mantissatable[i] = 0x38000000 + ((i - 1024) << 13);

	exponenttable[0] = 0;
	exponenttable[32] = 0x80000000;

	for (uint32 i = 0; i < 31; i++)
		exponenttable[i] = i << 23;

	for (uint32 i = 33; i < 63; i++)
		exponenttable[i] = 0x80000000 + ((i - 32) << 23);

	exponenttable[31] = 0x47800000;
	exponenttable[63] = 0xC7800000;

	for (int i = 0; i < 64; i++)
	{
		if (i == 0 || i == 32)
			offsettable[i] = 0;
		else
			offsettable[i] = 1024;
	}


	// tables for float -> half conversions.

	for (uint32 i = 0; i < 256; i++)
	{
		int e = (int) i - 127;

		if (e < -24) // Very small numbers map to zero
		{
			basetable[i | 0x000] = 0x0000;
			basetable[i | 0x100] = 0x8000;
			shifttable[i | 0x000] = 24;
			shifttable[i | 0x100] = 24;
		}
		else if (e < -14) // Small numbers map to denorms
		{
			basetable[i | 0x000] = (0x0400 >> (-e - 14));
			basetable[i | 0x100] = (0x0400 >> (-e - 14)) | 0x8000;
			shifttable[i | 0x000] = -e - 1;
			shifttable[i | 0x100] = -e - 1;
		}
		else if (e <= 15) // Normal numbers just lose precision
		{
			basetable[i | 0x000] = ((e + 15) << 10);
			basetable[i | 0x100] = ((e + 15) << 10) | 0x8000;
			shifttable[i | 0x000] = 13;
			shifttable[i | 0x100] = 13;
		}
		else if (e < 128) // Large numbers map to Infinity
		{
			basetable[i | 0x000] = 0x7C00;
			basetable[i | 0x100] = 0xFC00;
			shifttable[i | 0x000] = 24;
			shifttable[i | 0x100] = 24;
		}
		else // Infinity and NaN's stay Infinity and NaN's
		{
			basetable[i | 0x000] = 0x7C00;
			basetable[i | 0x100] = 0xFC00;
			shifttable[i | 0x000] = 13;
			shifttable[i | 0x100] = 13;
		}
	}
}

float halfToFloat(half h)
{
	union { float f; uint32 i; } conv;

	conv.i = mantissatable[offsettable[h >> 10] + (h & 0x3FF)] + exponenttable[h >> 10];
	return conv.f;
}

half floatToHalf(float f)
{
	union { float f; uint32 i; } conv;
	conv.f = f;

	return basetable[(conv.i >> 23) & 0x1FF] + ((conv.i & 0x007FFFFF) >> shifttable[(conv.i >> 23) & 0x1FF]);
}

} // love