toFloat.cpp

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//
// Copyright (c) 2002, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
// 
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// in the documentation and/or other materials provided with the
// distribution.
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// its contributors may be used to endorse or promote products derived
// from this software without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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//
 
 
 
 
//---------------------------------------------------------------------------
//
//      toFloat
//
//      A program to generate the lookup table for half-to-float
//      conversion needed by class half.
//      The program loops over all 65536 possible half numbers,
//      converts each of them to a float, and prints the result.
//
//---------------------------------------------------------------------------
 
 
#include <iostream>
#include <iomanip>
 
using namespace std;
 
//---------------------------------------------------
// Interpret an unsigned short bit pattern as a half,
// and convert that half to the corresponding float's
// bit pattern.
//---------------------------------------------------
 
unsigned int
halfToFloat (unsigned short y)
{
 
    int s = (y >> 15) & 0x00000001;
    int e = (y >> 10) & 0x0000001f;
    int m =  y        & 0x000003ff;
 
    if (e == 0)
    {
        if (m == 0)
        {
            //
            // Plus or minus zero
            //
 
            return s << 31;
        }
        else
        {
            //
            // Denormalized number -- renormalize it
            //
 
            while (!(m & 0x00000400))
            {
                m <<= 1;
                e -=  1;
            }
 
            e += 1;
            m &= ~0x00000400;
        }
    }
    else if (e == 31)
    {
        if (m == 0)
        {
            //
            // Positive or negative infinity
            //
 
            return (s << 31) | 0x7f800000;
        }
        else
        {
            //
            // Nan -- preserve sign and significand bits
            //
 
            return (s << 31) | 0x7f800000 | (m << 13);
        }
    }
 
    //
    // Normalized number
    //
 
    e = e + (127 - 15);
    m = m << 13;
 
    //
    // Assemble s, e and m.
    //
 
    return (s << 31) | (e << 23) | m;
}
 
 
//---------------------------------------------
// Main - prints the half-to-float lookup table
//---------------------------------------------
 
int
main ()
{
    cout.precision (9);
    cout.setf (ios_base::hex, ios_base::basefield);
 
    cout << "//\n"
            "// This is an automatically generated file.\n"
            "// Do not edit.\n"
            "//\n\n";
 
    cout << "{\n    ";
 
    const int iMax = (1 << 16);
 
    for (int i = 0; i < iMax; i++)
    {
        cout << "{0x" << setfill ('0') << setw (8) << halfToFloat (i) << "}, ";
 
        if (i % 4 == 3)
        {
            cout << "\n";
 
            if (i < iMax - 1)
                cout << "    ";
        }
    }
 
    cout << "};\n";
    return 0;
}