79 lines
3.3 KiB
C++
79 lines
3.3 KiB
C++
/****************************************************************************
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* VCGLib o o *
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* Visual and Computer Graphics Library o o *
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* _ O _ *
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* Copyright(C) 2004 \/)\/ *
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* Visual Computing Lab /\/| *
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* ISTI - Italian National Research Council | *
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* \ *
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* All rights reserved. *
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 2 of the License, or *
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* (at your option) any later version. *
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* *
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* This program is distributed in the hope that it will be useful, *
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* but WITHOUT ANY WARRANTY; without even the implied warranty of *
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
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* GNU General Public License (http://www.gnu.org/licenses/gpl.txt) *
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* for more details. *
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* *
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****************************************************************************/
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// RandomGenerator is derived from a STL extension of sgi:
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// it is based on the Subtractive Ring method.
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// See section 3.6 of Knuth for an implementation of the subtractive method in FORTRAN.
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// Section 3.2.2 of Knuth analyzes this class of algorithms.
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// (D. E. Knuth, The Art of Computer Programming. Volume 2: Seminumerical Algorithms, second edition. Addison-Wesley, 1981.) .
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// Note: this code assumes that int is 32 bits.
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#ifndef __VCG_RandomGenerator
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#define __VCG_RandomGenerator
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#include <functional>
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namespace vcg {
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namespace math {
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class RandomGenerator : public std::unary_function<unsigned int, unsigned int> {
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private:
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unsigned int _M_table[55];
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size_t _M_index1;
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size_t _M_index2;
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public:
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unsigned int operator()(unsigned int __limit) {
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_M_index1 = (_M_index1 + 1) % 55;
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_M_index2 = (_M_index2 + 1) % 55;
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_M_table[_M_index1] = _M_table[_M_index1] - _M_table[_M_index2];
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return _M_table[_M_index1] % __limit;
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}
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void _M_initialize(unsigned int __seed)
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{
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unsigned int __k = 1;
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_M_table[54] = __seed;
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size_t __i;
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for (__i = 0; __i < 54; __i++) {
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size_t __ii = (21 * (__i + 1) % 55) - 1;
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_M_table[__ii] = __k;
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__k = __seed - __k;
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__seed = _M_table[__ii];
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}
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for (int __loop = 0; __loop < 4; __loop++) {
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for (__i = 0; __i < 55; __i++)
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_M_table[__i] = _M_table[__i] - _M_table[(1 + __i + 30) % 55];
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}
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_M_index1 = 0;
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_M_index2 = 31;
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}
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RandomGenerator(unsigned int __seed) { _M_initialize(__seed); }
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RandomGenerator() { _M_initialize(161803398u); }
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};
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} // end namespace math
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} // end namespace vcg
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#endif
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