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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <cstdlib>
#include <cstdint>
namespace vespalib {
/*
* Simple random generator based on lrand48() spec.
*/
class Rand48
{
private:
uint64_t _state;
public:
void srand48(long seed) {
_state = ((static_cast<uint64_t>(seed & 0xffffffffu)) << 16) + 0x330e;
}
Rand48()
: Rand48(0x1234abcd)
{ }
explicit Rand48(long seed)
: _state(0)
{
srand48(seed);
}
void iterate() {
_state = (UINT64_C(0x5DEECE66D) * _state + 0xb) &
UINT64_C(0xFFFFFFFFFFFF);
}
/*
* Return value from 0 to 2^31 - 1
*/
long lrand48() {
iterate();
return static_cast<long>(_state >> 17);
}
};
}
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