eLut.cpp

///////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2002, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
// 
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#include <iostream>
#include <iomanip>

using namespace std;

//-----------------------------------------------------
// Compute a lookup table for float-to-half conversion.
//
// When indexed with the combined sign and exponent of
// a float, the table either returns the combined sign
// and exponent of the corresponding half, or zero if
// the corresponding half may not be normalized (zero,
// denormalized, overflow).
//-----------------------------------------------------

void
initELut (unsigned short eLut[])
{
    for (int i = 0; i < 0x100; i++)
    {
	int e = (i & 0x0ff) - (127 - 15);

	if (e <= 0 || e >= 30)
	{
	    //
	    // Special case
	    //

	    eLut[i]         = 0;
	    eLut[i | 0x100] = 0;
	}
	else
	{
	    //
	    // Common case - normalized half, no exponent overflow possible
	    //

	    eLut[i]         =  (e << 10);
	    eLut[i | 0x100] = ((e << 10) | 0x8000);
	}
    }
}


//------------------------------------------------------------
// Main - prints the sign-and-exponent conversion lookup table
//------------------------------------------------------------

int
main ()
{
    const int tableSize = 1 << 9;
    unsigned short eLut[tableSize];
    initELut (eLut);

    cout << "//\n"
	    "// This is an automatically generated file.\n"
	    "// Do not edit.\n"
	    "//\n\n";

    cout << "{\n    ";

    for (int i = 0; i < tableSize; i++)
    {
	cout << setw (5) << eLut[i] << ", ";

	if (i % 8 == 7)
	{
	    cout << "\n";

	    if (i < tableSize - 1)
		cout << "    ";
	}
    }

    cout << "};\n";
    return 0;
}