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using System.Numerics;
namespace Ryujinx.HLE.HOS.Kernel.Common
{
class MersenneTwister
{
private int _index;
private uint[] _mt;
public MersenneTwister(uint seed)
{
_mt = new uint[624];
_mt[0] = seed;
for (int mtIdx = 1; mtIdx < _mt.Length; mtIdx++)
{
uint prev = _mt[mtIdx - 1];
_mt[mtIdx] = (uint)(0x6c078965 * (prev ^ (prev >> 30)) + mtIdx);
}
_index = _mt.Length;
}
public long GenRandomNumber(long min, long max)
{
long range = max - min;
if (min == max)
{
return min;
}
if (range == -1)
{
// Increment would cause a overflow, special case.
return GenRandomNumber(2, 2, 32, 0xffffffffu, 0xffffffffu);
}
range++;
// This is log2(Range) plus one.
int nextRangeLog2 = 64 - BitOperations.LeadingZeroCount((ulong)range);
// If Range is already power of 2, subtract one to use log2(Range) directly.
int rangeLog2 = nextRangeLog2 - (BitOperations.IsPow2(range) ? 1 : 0);
int parts = rangeLog2 > 32 ? 2 : 1;
int bitsPerPart = rangeLog2 / parts;
int fullParts = parts - (rangeLog2 - parts * bitsPerPart);
uint mask = 0xffffffffu >> (32 - bitsPerPart);
uint maskPlus1 = 0xffffffffu >> (31 - bitsPerPart);
long randomNumber;
do
{
randomNumber = GenRandomNumber(parts, fullParts, bitsPerPart, mask, maskPlus1);
}
while ((ulong)randomNumber >= (ulong)range);
return min + randomNumber;
}
private long GenRandomNumber(
int parts,
int fullParts,
int bitsPerPart,
uint mask,
uint maskPlus1)
{
long randomNumber = 0;
int part = 0;
for (; part < fullParts; part++)
{
randomNumber <<= bitsPerPart;
randomNumber |= GenRandomNumber() & mask;
}
for (; part < parts; part++)
{
randomNumber <<= bitsPerPart + 1;
randomNumber |= GenRandomNumber() & maskPlus1;
}
return randomNumber;
}
private uint GenRandomNumber()
{
if (_index >= _mt.Length)
{
Twist();
}
uint value = _mt[_index++];
value ^= value >> 11;
value ^= (value << 7) & 0x9d2c5680;
value ^= (value << 15) & 0xefc60000;
value ^= value >> 18;
return value;
}
private void Twist()
{
for (int mtIdx = 0; mtIdx < _mt.Length; mtIdx++)
{
uint value = (_mt[mtIdx] & 0x80000000) + (_mt[(mtIdx + 1) % _mt.Length] & 0x7fffffff);
_mt[mtIdx] = _mt[(mtIdx + 397) % _mt.Length] ^ (value >> 1);
if ((value & 1) != 0)
{
_mt[mtIdx] ^= 0x9908b0df;
}
}
_index = 0;
}
}
}
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