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108 lines
3.1 KiB
108 lines
3.1 KiB
11 years ago
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/*
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* Copyright 2008-2012 NVIDIA Corporation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <thrust/detail/cstdint.h>
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#include <thrust/random/detail/mod.h>
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namespace thrust
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{
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namespace random
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{
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namespace detail
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{
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template<typename UIntType, UIntType a, unsigned long long c, UIntType m>
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struct linear_congruential_engine_discard_implementation
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{
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__host__ __device__
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static void discard(UIntType &state, unsigned long long z)
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{
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for(; z > 0; --z)
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{
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state = detail::mod<UIntType,a,c,m>(state);
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}
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}
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}; // end linear_congruential_engine_discard
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// specialize for small integers and c == 0
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// XXX figure out a robust implemenation of this for any unsigned integer type later
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template<thrust::detail::uint32_t a, thrust::detail::uint32_t m>
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struct linear_congruential_engine_discard_implementation<thrust::detail::uint32_t,a,0,m>
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{
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__host__ __device__
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static void discard(thrust::detail::uint32_t &state, unsigned long long z)
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{
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const thrust::detail::uint32_t modulus = m;
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// XXX we need to use unsigned long long here or we will encounter overflow in the
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// multiplies below
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// figure out a robust implementation of this later
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unsigned long long multiplier = a;
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unsigned long long multiplier_to_z = 1;
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// see http://en.wikipedia.org/wiki/Modular_exponentiation
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while(z > 0)
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{
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if(z & 1)
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{
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// multiply in this bit's contribution while using modulus to keep result small
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multiplier_to_z = (multiplier_to_z * multiplier) % modulus;
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}
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// move to the next bit of the exponent, square (and mod) the base accordingly
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z >>= 1;
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multiplier = (multiplier * multiplier) % modulus;
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}
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state = static_cast<thrust::detail::uint32_t>((multiplier_to_z * state) % modulus);
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}
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}; // end linear_congruential_engine_discard
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struct linear_congruential_engine_discard
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{
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template<typename LinearCongruentialEngine>
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__host__ __device__
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static void discard(LinearCongruentialEngine &lcg, unsigned long long z)
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{
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typedef typename LinearCongruentialEngine::result_type result_type;
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const result_type c = LinearCongruentialEngine::increment;
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const result_type a = LinearCongruentialEngine::multiplier;
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const result_type m = LinearCongruentialEngine::modulus;
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// XXX WAR unused variable warnings
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(void) c;
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(void) a;
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(void) m;
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linear_congruential_engine_discard_implementation<result_type,a,c,m>::discard(lcg.m_x, z);
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}
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}; // end linear_congruential_engine_discard
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} // end detail
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} // end random
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} // end thrust
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