6e8fbca745
match the genesis editor version 1.3.0.653.
301 lines
11 KiB
C++
301 lines
11 KiB
C++
/* boost random/uniform_int.hpp header file
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*
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* Copyright Jens Maurer 2000-2001
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* Distributed under the Boost Software License, Version 1.0. (See
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* accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* See http://www.boost.org for most recent version including documentation.
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*
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* $Id: uniform_int.hpp 60755 2010-03-22 00:45:06Z steven_watanabe $
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*
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* Revision history
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* 2001-04-08 added min<max assertion (N. Becker)
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* 2001-02-18 moved to individual header files
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*/
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#ifndef BOOST_RANDOM_UNIFORM_INT_HPP
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#define BOOST_RANDOM_UNIFORM_INT_HPP
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#include <cassert>
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#include <iostream>
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#include <boost/config.hpp>
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#include <boost/limits.hpp>
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#include <boost/static_assert.hpp>
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#include <boost/detail/workaround.hpp>
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#include <boost/random/detail/config.hpp>
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#include <boost/random/detail/signed_unsigned_tools.hpp>
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#include <boost/type_traits/make_unsigned.hpp>
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namespace boost {
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/**
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* The distribution function uniform_int models a \random_distribution.
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* On each invocation, it returns a random integer value uniformly
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* distributed in the set of integer numbers {min, min+1, min+2, ..., max}.
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*
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* The template parameter IntType shall denote an integer-like value type.
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*/
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template<class IntType = int>
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class uniform_int
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{
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public:
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typedef IntType input_type;
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typedef IntType result_type;
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/// \cond hide_private_members
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typedef typename make_unsigned<result_type>::type range_type;
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/// \endcond
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/**
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* Constructs a uniform_int object. @c min and @c max are
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* the parameters of the distribution.
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*
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* Requires: min <= max
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*/
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explicit uniform_int(IntType min_arg = 0, IntType max_arg = 9)
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: _min(min_arg), _max(max_arg)
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{
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#ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
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// MSVC fails BOOST_STATIC_ASSERT with std::numeric_limits at class scope
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BOOST_STATIC_ASSERT(std::numeric_limits<IntType>::is_integer);
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#endif
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assert(min_arg <= max_arg);
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init();
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}
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/**
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* Returns: The "min" parameter of the distribution
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*/
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result_type min BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _min; }
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/**
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* Returns: The "max" parameter of the distribution
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*/
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result_type max BOOST_PREVENT_MACRO_SUBSTITUTION () const { return _max; }
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void reset() { }
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// can't have member function templates out-of-line due to MSVC bugs
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template<class Engine>
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result_type operator()(Engine& eng)
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{
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return generate(eng, _min, _max, _range);
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}
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template<class Engine>
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result_type operator()(Engine& eng, result_type n)
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{
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assert(n > 0);
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if (n == 1)
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{
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return 0;
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}
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return generate(eng, 0, n - 1, n - 1);
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}
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#ifndef BOOST_RANDOM_NO_STREAM_OPERATORS
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template<class CharT, class Traits>
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friend std::basic_ostream<CharT,Traits>&
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operator<<(std::basic_ostream<CharT,Traits>& os, const uniform_int& ud)
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{
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os << ud._min << " " << ud._max;
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return os;
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}
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template<class CharT, class Traits>
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friend std::basic_istream<CharT,Traits>&
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operator>>(std::basic_istream<CharT,Traits>& is, uniform_int& ud)
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{
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is >> std::ws >> ud._min >> std::ws >> ud._max;
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ud.init();
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return is;
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}
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#endif
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private:
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#ifdef BOOST_MSVC
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#pragma warning(push)
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// disable division by zero warning, since we can't
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// actually divide by zero.
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#pragma warning(disable:4723)
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#endif
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/// \cond hide_private_members
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template<class Engine>
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static result_type generate(Engine& eng, result_type min_value, result_type /*max_value*/, range_type range)
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{
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typedef typename Engine::result_type base_result;
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// ranges are always unsigned
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typedef typename make_unsigned<base_result>::type base_unsigned;
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const base_result bmin = (eng.min)();
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const base_unsigned brange =
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random::detail::subtract<base_result>()((eng.max)(), (eng.min)());
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if(range == 0) {
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return min_value;
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} else if(brange == range) {
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// this will probably never happen in real life
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// basically nothing to do; just take care we don't overflow / underflow
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base_unsigned v = random::detail::subtract<base_result>()(eng(), bmin);
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return random::detail::add<base_unsigned, result_type>()(v, min_value);
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} else if(brange < range) {
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// use rejection method to handle things like 0..3 --> 0..4
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for(;;) {
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// concatenate several invocations of the base RNG
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// take extra care to avoid overflows
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// limit == floor((range+1)/(brange+1))
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// Therefore limit*(brange+1) <= range+1
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range_type limit;
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if(range == (std::numeric_limits<range_type>::max)()) {
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limit = range/(range_type(brange)+1);
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if(range % (range_type(brange)+1) == range_type(brange))
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++limit;
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} else {
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limit = (range+1)/(range_type(brange)+1);
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}
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// We consider "result" as expressed to base (brange+1):
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// For every power of (brange+1), we determine a random factor
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range_type result = range_type(0);
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range_type mult = range_type(1);
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// loop invariants:
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// result < mult
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// mult <= range
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while(mult <= limit) {
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// Postcondition: result <= range, thus no overflow
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//
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// limit*(brange+1)<=range+1 def. of limit (1)
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// eng()-bmin<=brange eng() post. (2)
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// and mult<=limit. loop condition (3)
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// Therefore mult*(eng()-bmin+1)<=range+1 by (1),(2),(3) (4)
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// Therefore mult*(eng()-bmin)+mult<=range+1 rearranging (4) (5)
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// result<mult loop invariant (6)
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// Therefore result+mult*(eng()-bmin)<range+1 by (5), (6) (7)
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//
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// Postcondition: result < mult*(brange+1)
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//
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// result<mult loop invariant (1)
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// eng()-bmin<=brange eng() post. (2)
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// Therefore result+mult*(eng()-bmin) <
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// mult+mult*(eng()-bmin) by (1) (3)
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// Therefore result+(eng()-bmin)*mult <
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// mult+mult*brange by (2), (3) (4)
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// Therefore result+(eng()-bmin)*mult <
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// mult*(brange+1) by (4)
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result += static_cast<range_type>(random::detail::subtract<base_result>()(eng(), bmin) * mult);
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// equivalent to (mult * (brange+1)) == range+1, but avoids overflow.
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if(mult * range_type(brange) == range - mult + 1) {
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// The destination range is an integer power of
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// the generator's range.
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return(result);
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}
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// Postcondition: mult <= range
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//
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// limit*(brange+1)<=range+1 def. of limit (1)
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// mult<=limit loop condition (2)
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// Therefore mult*(brange+1)<=range+1 by (1), (2) (3)
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// mult*(brange+1)!=range+1 preceding if (4)
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// Therefore mult*(brange+1)<range+1 by (3), (4) (5)
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//
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// Postcondition: result < mult
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//
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// See the second postcondition on the change to result.
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mult *= range_type(brange)+range_type(1);
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}
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// loop postcondition: range/mult < brange+1
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//
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// mult > limit loop condition (1)
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// Suppose range/mult >= brange+1 Assumption (2)
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// range >= mult*(brange+1) by (2) (3)
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// range+1 > mult*(brange+1) by (3) (4)
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// range+1 > (limit+1)*(brange+1) by (1), (4) (5)
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// (range+1)/(brange+1) > limit+1 by (5) (6)
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// limit < floor((range+1)/(brange+1)) by (6) (7)
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// limit==floor((range+1)/(brange+1)) def. of limit (8)
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// not (2) reductio (9)
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//
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// loop postcondition: (range/mult)*mult+(mult-1) >= range
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//
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// (range/mult)*mult + range%mult == range identity (1)
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// range%mult < mult def. of % (2)
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// (range/mult)*mult+mult > range by (1), (2) (3)
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// (range/mult)*mult+(mult-1) >= range by (3) (4)
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//
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// Note that the maximum value of result at this point is (mult-1),
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// so after this final step, we generate numbers that can be
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// at least as large as range. We have to really careful to avoid
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// overflow in this final addition and in the rejection. Anything
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// that overflows is larger than range and can thus be rejected.
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// range/mult < brange+1 -> no endless loop
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range_type result_increment = uniform_int<range_type>(0, range/mult)(eng);
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if((std::numeric_limits<range_type>::max)() / mult < result_increment) {
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// The multiplcation would overflow. Reject immediately.
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continue;
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}
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result_increment *= mult;
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// unsigned integers are guaranteed to wrap on overflow.
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result += result_increment;
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if(result < result_increment) {
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// The addition overflowed. Reject.
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continue;
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}
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if(result > range) {
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// Too big. Reject.
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continue;
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}
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return random::detail::add<range_type, result_type>()(result, min_value);
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}
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} else { // brange > range
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base_unsigned bucket_size;
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// it's safe to add 1 to range, as long as we cast it first,
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// because we know that it is less than brange. However,
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// we do need to be careful not to cause overflow by adding 1
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// to brange.
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if(brange == (std::numeric_limits<base_unsigned>::max)()) {
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bucket_size = brange / (static_cast<base_unsigned>(range)+1);
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if(brange % (static_cast<base_unsigned>(range)+1) == static_cast<base_unsigned>(range)) {
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++bucket_size;
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}
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} else {
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bucket_size = (brange+1) / (static_cast<base_unsigned>(range)+1);
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}
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for(;;) {
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base_unsigned result =
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random::detail::subtract<base_result>()(eng(), bmin);
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result /= bucket_size;
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// result and range are non-negative, and result is possibly larger
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// than range, so the cast is safe
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if(result <= static_cast<base_unsigned>(range))
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return random::detail::add<base_unsigned, result_type>()(result, min_value);
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}
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}
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}
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#ifdef BOOST_MSVC
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#pragma warning(pop)
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#endif
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void init()
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{
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_range = random::detail::subtract<result_type>()(_max, _min);
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}
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/// \endcond
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// The result_type may be signed or unsigned, but the _range is always
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// unsigned.
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result_type _min, _max;
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range_type _range;
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};
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} // namespace boost
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#endif // BOOST_RANDOM_UNIFORM_INT_HPP
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