///////////////////////////////////////////////////////////////////////////

//

// Copyright (c) 2002, Industrial Light & Magic, a division of Lucas

// Digital Ltd. LLC

// 

// All rights reserved.

// 

// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions are

// met:

// *       Redistributions of source code must retain the above copyright

// notice, this list of conditions and the following disclaimer.

// *       Redistributions in binary form must reproduce the above

// copyright notice, this list of conditions and the following disclaimer

// in the documentation and/or other materials provided with the

// distribution.

// *       Neither the name of Industrial Light & Magic nor the names of

// 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

// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR

// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT

// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,

// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT

// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

//

///////////////////////////////////////////////////////////////////////////

// Primary authors:

//     Florian Kainz <kainz@ilm.com>

//     Rod Bogart <rgb@ilm.com>

//---------------------------------------------------------------------------

//

//  class half --

//  implementation of non-inline members

//

//---------------------------------------------------------------------------

#include <assert.h>

#include "half.h"

using namespace std;

//-------------------------------------------------------------

// Lookup tables for half-to-float and float-to-half conversion

//-------------------------------------------------------------

HALF_EXPORT const half::uif half::_toFloat[1 << 16] =

    #include "toFloat.h"

HALF_EXPORT const unsigned short half::_eLut[1 << 9] =

    #include "eLut.h"

//-----------------------------------------------

// Overflow handler for float-to-half conversion;

// generates a hardware floating-point overflow,

// which may be trapped by the operating system.

//-----------------------------------------------

HALF_EXPORT float

half::overflow ()

{

    volatile float f = 1e10;

    for (int i = 0; i < 10; i++) 

  f *= f;       // this will overflow before

          // the for­loop terminates

    return f;

}

//-----------------------------------------------------

// Float-to-half conversion -- general case, including

// zeroes, denormalized numbers and exponent overflows.

//-----------------------------------------------------

HALF_EXPORT short

half::convert (int i)

{

    //

    // Our floating point number, f, is represented by the bit

    // pattern in integer i.  Disassemble that bit pattern into

    // the sign, s, the exponent, e, and the significand, m.

    // Shift s into the position where it will go in in the

    // resulting half number.

    // Adjust e, accounting for the different exponent bias

    // of float and half (127 versus 15).

    //

    register int s =  (i >> 16) & 0x00008000;

    register int e = ((i >> 23) & 0x000000ff) - (127 - 15);

    register int m =   i        & 0x007fffff;

    //

    // Now reassemble s, e and m into a half:

    //

    if (e <= 0)

    {

  if (e < -10)

  {

      //

      // E is less than -10.  The absolute value of f is

      // less than HALF_MIN (f may be a small normalized

      // float, a denormalized float or a zero).

      //

      // We convert f to a half zero with the same sign as f.

      //

      return s;

  }

  //

  // E is between -10 and 0.  F is a normalized float

  // whose magnitude is less than HALF_NRM_MIN.

  //

  // We convert f to a denormalized half.

  //

  //

  // Add an explicit leading 1 to the significand.

  // 

  m = m | 0x00800000;

  //

  // Round to m to the nearest (10+e)-bit value (with e between

  // -10 and 0); in case of a tie, round to the nearest even value.

  //

  // Rounding may cause the significand to overflow and make

  // our number normalized.  Because of the way a half's bits

  // are laid out, we don't have to treat this case separately;

  // the code below will handle it correctly.

  // 

  int t = 14 - e;

  int a = (1 << (t - 1)) - 1;

  int b = (m >> t) & 1;

  m = (m + a + b) >> t;

  //

  // Assemble the half from s, e (zero) and m.

  //

  return s | m;

    }

    else if (e == 0xff - (127 - 15))

    {

  if (m == 0)

  {

      //

      // F is an infinity; convert f to a half

      // infinity with the same sign as f.

      //

      return s | 0x7c00;

  }

  else

  {

      //

      // F is a NAN; we produce a half NAN that preserves

      // the sign bit and the 10 leftmost bits of the

      // significand of f, with one exception: If the 10

      // leftmost bits are all zero, the NAN would turn 

      // into an infinity, so we have to set at least one

      // bit in the significand.

      //

      m >>= 13;

      return s | 0x7c00 | m | (m == 0);

  }

    }

    else

    {

  //

  // E is greater than zero.  F is a normalized float.

  // We try to convert f to a normalized half.

  //

  //

  // Round to m to the nearest 10-bit value.  In case of

  // a tie, round to the nearest even value.

  //

  m = m + 0x00000fff + ((m >> 13) & 1);

  if (m & 0x00800000)

  {

      m =  0;   // overflow in significand,

      e += 1;   // adjust exponent

  }

  //

  // Handle exponent overflow

  //

  if (e > 30)

  {

      overflow ();  // Cause a hardware floating point overflow;

      return s | 0x7c00;  // if this returns, the half becomes an

  }        // infinity with the same sign as f.

  //

  // Assemble the half from s, e and m.

  //

  return s | (e << 10) | (m >> 13);

    }

}

//---------------------

// Stream I/O operators

//---------------------

HALF_EXPORT ostream &

operator << (ostream &os, half h)

{

    os << float (h);

    return os;

}

HALF_EXPORT istream &

operator >> (istream &is, half &h)

{

    float f;

    is >> f;

    h = half (f);

    return is;

}

//---------------------------------------

// Functions to print the bit-layout of

// floats and halfs, mostly for debugging

//---------------------------------------

HALF_EXPORT void

printBits (ostream &os, half h)

{

    unsigned short b = h.bits();

    for (int i = 15; i >= 0; i--)

    {

  os << (((b >> i) & 1)? '1': '0');

  if (i == 15 || i == 10)

      os << ' ';

    }

}

HALF_EXPORT void

printBits (ostream &os, float f)

{

    half::uif x;

    x.f = f;

    for (int i = 31; i >= 0; i--)

    {

  os << (((x.i >> i) & 1)? '1': '0');

  if (i == 31 || i == 23)

      os << ' ';

    }

}

HALF_EXPORT void

printBits (char c[19], half h)

{

    unsigned short b = h.bits();

    for (int i = 15, j = 0; i >= 0; i--, j++)

    {

  c[j] = (((b >> i) & 1)? '1': '0');

  if (i == 15 || i == 10)

      c[++j] = ' ';

    }

    c[18] = 0;

}

HALF_EXPORT void

printBits (char c[35], float f)

{

    half::uif x;

    x.f = f;

    for (int i = 31, j = 0; i >= 0; i--, j++)

    {

  c[j] = (((x.i >> i) & 1)? '1': '0');

  if (i == 31 || i == 23)

      c[++j] = ' ';

    }

    c[34] = 0;

}