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///////////////////////////////////////////////////////////////
// Copyright 2012 John Maddock. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/random.hpp>
#include <boost/functional/hash.hpp>
#include <unordered_set>
#include <city.h>
//[hash1
/*`
All of the types in this library support hashing via boost::hash or std::hash.
That means we can use multiprecision types directly in hashed containers such as std::unordered_set:
*/
//]
void t1()
{
//[hash2
using namespace boost::multiprecision;
using namespace boost::random;
mt19937 mt;
uniform_int_distribution<uint256_t> ui;
std::unordered_set<uint256_t> set;
// Put 1000 random values into the container:
for(unsigned i = 0; i < 1000; ++i)
set.insert(ui(mt));
//]
}
//[hash3
/*`
Or we can define our own hash function, for example in this case based on
Google's CityHash:
*/
struct cityhash
{
std::size_t operator()(const boost::multiprecision::uint256_t& val)const
{
// create a hash from all the limbs of the argument, this function is probably x64 specific,
// and requires that we access the internals of the data type:
std::size_t result = CityHash64(reinterpret_cast<const char*>(val.backend().limbs()), val.backend().size() * sizeof(val.backend().limbs()[0]));
// modify the returned hash based on sign:
return val < 0 ? ~result : result;
}
};
//]
void t2()
{
//[hash4
/*`As before insert some values into a container, this time using our custom hasher:*/
std::unordered_set<uint256_t, cityhash> set2;
for(unsigned i = 0; i < 1000; ++i)
set2.insert(ui(mt));
//]
}
int main()
{
t1();
t2();
return 0;
}
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