312 lines
7.6 KiB
C++
312 lines
7.6 KiB
C++
///////////////////////////////////////////////////////////////////////////
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//
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// Copyright (c) 2002, Industrial Light & Magic, a division of Lucas
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// Digital Ltd. LLC
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Industrial Light & Magic nor the names of
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// its contributors may be used to endorse or promote products derived
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// from this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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///////////////////////////////////////////////////////////////////////////
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// Primary authors:
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// Florian Kainz <kainz@ilm.com>
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// Rod Bogart <rgb@ilm.com>
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//---------------------------------------------------------------------------
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//
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// class half --
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// implementation of non-inline members
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//
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//---------------------------------------------------------------------------
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#include <assert.h>
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#include "half.h"
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using namespace std;
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//-------------------------------------------------------------
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// Lookup tables for half-to-float and float-to-half conversion
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//-------------------------------------------------------------
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HALF_EXPORT_CONST half::uif half::_toFloat[1 << 16] =
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#include "toFloat.h"
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HALF_EXPORT_CONST unsigned short half::_eLut[1 << 9] =
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#include "eLut.h"
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//-----------------------------------------------
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// Overflow handler for float-to-half conversion;
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// generates a hardware floating-point overflow,
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// which may be trapped by the operating system.
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//-----------------------------------------------
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float
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half::overflow ()
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{
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volatile float f = 1e10;
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for (int i = 0; i < 10; i++)
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f *= f; // this will overflow before
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// the for<6F>loop terminates
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return f;
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}
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//-----------------------------------------------------
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// Float-to-half conversion -- general case, including
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// zeroes, denormalized numbers and exponent overflows.
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//-----------------------------------------------------
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short
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half::convert (int i)
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{
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//
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// Our floating point number, f, is represented by the bit
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// pattern in integer i. Disassemble that bit pattern into
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// the sign, s, the exponent, e, and the significand, m.
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// Shift s into the position where it will go in in the
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// resulting half number.
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// Adjust e, accounting for the different exponent bias
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// of float and half (127 versus 15).
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//
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register int s = (i >> 16) & 0x00008000;
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register int e = ((i >> 23) & 0x000000ff) - (127 - 15);
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register int m = i & 0x007fffff;
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//
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// Now reassemble s, e and m into a half:
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//
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if (e <= 0)
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{
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if (e < -10)
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{
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//
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// E is less than -10. The absolute value of f is
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// less than HALF_MIN (f may be a small normalized
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// float, a denormalized float or a zero).
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//
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// We convert f to a half zero with the same sign as f.
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//
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return s;
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}
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//
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// E is between -10 and 0. F is a normalized float
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// whose magnitude is less than HALF_NRM_MIN.
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//
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// We convert f to a denormalized half.
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//
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//
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// Add an explicit leading 1 to the significand.
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//
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m = m | 0x00800000;
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//
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// Round to m to the nearest (10+e)-bit value (with e between
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// -10 and 0); in case of a tie, round to the nearest even value.
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//
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// Rounding may cause the significand to overflow and make
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// our number normalized. Because of the way a half's bits
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// are laid out, we don't have to treat this case separately;
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// the code below will handle it correctly.
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//
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int t = 14 - e;
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int a = (1 << (t - 1)) - 1;
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int b = (m >> t) & 1;
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m = (m + a + b) >> t;
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//
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// Assemble the half from s, e (zero) and m.
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//
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return s | m;
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}
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else if (e == 0xff - (127 - 15))
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{
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if (m == 0)
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{
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//
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// F is an infinity; convert f to a half
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// infinity with the same sign as f.
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//
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return s | 0x7c00;
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}
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else
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{
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//
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// F is a NAN; we produce a half NAN that preserves
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// the sign bit and the 10 leftmost bits of the
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// significand of f, with one exception: If the 10
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// leftmost bits are all zero, the NAN would turn
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// into an infinity, so we have to set at least one
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// bit in the significand.
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//
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m >>= 13;
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return s | 0x7c00 | m | (m == 0);
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}
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}
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else
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{
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//
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// E is greater than zero. F is a normalized float.
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// We try to convert f to a normalized half.
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//
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//
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// Round to m to the nearest 10-bit value. In case of
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// a tie, round to the nearest even value.
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//
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m = m + 0x00000fff + ((m >> 13) & 1);
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if (m & 0x00800000)
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{
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m = 0; // overflow in significand,
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e += 1; // adjust exponent
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}
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//
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// Handle exponent overflow
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//
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if (e > 30)
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{
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overflow (); // Cause a hardware floating point overflow;
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return s | 0x7c00; // if this returns, the half becomes an
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} // infinity with the same sign as f.
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//
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// Assemble the half from s, e and m.
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//
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return s | (e << 10) | (m >> 13);
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}
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}
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//---------------------
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// Stream I/O operators
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//---------------------
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ostream &
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operator << (ostream &os, half h)
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{
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os << float (h);
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return os;
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}
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istream &
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operator >> (istream &is, half &h)
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{
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float f;
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is >> f;
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h = half (f);
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return is;
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}
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//---------------------------------------
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// Functions to print the bit-layout of
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// floats and halfs, mostly for debugging
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//---------------------------------------
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void
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printBits (ostream &os, half h)
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{
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unsigned short b = h.bits();
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for (int i = 15; i >= 0; i--)
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{
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os << (((b >> i) & 1)? '1': '0');
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if (i == 15 || i == 10)
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os << ' ';
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}
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}
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void
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printBits (ostream &os, float f)
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{
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half::uif x;
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x.f = f;
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for (int i = 31; i >= 0; i--)
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{
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os << (((x.i >> i) & 1)? '1': '0');
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if (i == 31 || i == 23)
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os << ' ';
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}
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}
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void
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printBits (char c[19], half h)
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{
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unsigned short b = h.bits();
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for (int i = 15, j = 0; i >= 0; i--, j++)
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{
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c[j] = (((b >> i) & 1)? '1': '0');
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if (i == 15 || i == 10)
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c[++j] = ' ';
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}
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c[18] = 0;
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}
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void
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printBits (char c[35], float f)
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{
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half::uif x;
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x.f = f;
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for (int i = 31, j = 0; i >= 0; i--, j++)
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{
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c[j] = (((x.i >> i) & 1)? '1': '0');
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if (i == 31 || i == 23)
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c[++j] = ' ';
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}
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c[34] = 0;
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}
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