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107 lines
3.1 KiB
107 lines
3.1 KiB
/* |
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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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