Disabled external gits
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cs440-acg/ext/openexr/IlmBase/Imath/ImathRandom.cpp
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194
cs440-acg/ext/openexr/IlmBase/Imath/ImathRandom.cpp
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///////////////////////////////////////////////////////////////////////////
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//
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// Copyright (c) 2002-2012, 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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//-----------------------------------------------------------------------------
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//
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// Routines that generate pseudo-random numbers compatible
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// with the standard erand48(), nrand48(), etc. functions.
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//
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//-----------------------------------------------------------------------------
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#include "ImathRandom.h"
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#include "ImathInt64.h"
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IMATH_INTERNAL_NAMESPACE_SOURCE_ENTER
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namespace {
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//
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// Static state used by Imath::drand48(), Imath::lrand48() and Imath::srand48()
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//
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unsigned short staticState[3] = {0, 0, 0};
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void
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rand48Next (unsigned short state[3])
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{
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//
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// drand48() and friends are all based on a linear congruential
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// sequence,
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//
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// x[n+1] = (a * x[n] + c) % m,
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//
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// where a and c are as specified below, and m == (1 << 48)
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//
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static const Int64 a = Int64 (0x5deece66dLL);
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static const Int64 c = Int64 (0xbLL);
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//
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// Assemble the 48-bit value x[n] from the
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// three 16-bit values stored in state.
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//
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Int64 x = (Int64 (state[2]) << 32) |
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(Int64 (state[1]) << 16) |
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Int64 (state[0]);
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//
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// Compute x[n+1], except for the "modulo m" part.
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//
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x = a * x + c;
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//
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// Disassemble the 48 least significant bits of x[n+1] into
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// three 16-bit values. Discard the 16 most significant bits;
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// this takes care of the "modulo m" operation.
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//
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// We assume that sizeof (unsigned short) == 2.
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//
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state[2] = (unsigned short)(x >> 32);
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state[1] = (unsigned short)(x >> 16);
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state[0] = (unsigned short)(x);
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}
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} // namespace
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double
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erand48 (unsigned short state[3])
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{
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//
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// Generate double-precision floating-point values between 0.0 and 1.0:
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//
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// The exponent is set to 0x3ff, which indicates a value greater
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// than or equal to 1.0, and less than 2.0. The 48 most significant
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// bits of the significand (mantissa) are filled with pseudo-random
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// bits generated by rand48Next(). The remaining 4 bits are a copy
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// of the 4 most significant bits of the significand. This results
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// in bit patterns between 0x3ff0000000000000 and 0x3fffffffffffffff,
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// which correspond to uniformly distributed floating-point values
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// between 1.0 and 1.99999999999999978. Subtracting 1.0 from those
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// values produces numbers between 0.0 and 0.99999999999999978, that
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// is, between 0.0 and 1.0-DBL_EPSILON.
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//
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rand48Next (state);
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union {double d; Int64 i;} u;
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u.i = (Int64 (0x3ff) << 52) | // sign and exponent
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(Int64 (state[2]) << 36) | // significand
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(Int64 (state[1]) << 20) |
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(Int64 (state[0]) << 4) |
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(Int64 (state[2]) >> 12);
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return u.d - 1;
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}
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double
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drand48 ()
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{
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return IMATH_INTERNAL_NAMESPACE::erand48 (staticState);
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}
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long int
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nrand48 (unsigned short state[3])
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{
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//
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// Generate uniformly distributed integers between 0 and 0x7fffffff.
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//
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rand48Next (state);
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return ((long int) (state[2]) << 15) |
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((long int) (state[1]) >> 1);
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}
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long int
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lrand48 ()
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{
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return IMATH_INTERNAL_NAMESPACE::nrand48 (staticState);
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}
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void
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srand48 (long int seed)
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{
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staticState[2] = (unsigned short)(seed >> 16);
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staticState[1] = (unsigned short)(seed);
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staticState[0] = 0x330e;
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}
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float
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Rand32::nextf ()
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{
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//
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// Generate single-precision floating-point values between 0.0 and 1.0:
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//
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// The exponent is set to 0x7f, which indicates a value greater than
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// or equal to 1.0, and less than 2.0. The 23 bits of the significand
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// (mantissa) are filled with pseudo-random bits generated by
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// Rand32::next(). This results in in bit patterns between 0x3f800000
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// and 0x3fffffff, which correspond to uniformly distributed floating-
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// point values between 1.0 and 1.99999988. Subtracting 1.0 from
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// those values produces numbers between 0.0 and 0.99999988, that is,
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// between 0.0 and 1.0-FLT_EPSILON.
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//
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next ();
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union {float f; unsigned int i;} u;
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u.i = 0x3f800000 | (_state & 0x7fffff);
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return u.f - 1;
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}
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IMATH_INTERNAL_NAMESPACE_SOURCE_EXIT
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