/// <summary>
/// Randomly permute the specified number of elements in the supplied
/// array starting at the specified index.
/// </summary>
public static void Randomize <T>(
this IRandomUniform rnd, T[] array, long start, long count)
{
for (long i = start, e = start + count; i < e; i++)
{
array.Swap(i, start + rnd.UniformLong(count));
}
}
/// <summary>
/// Returns a uniform long which is guaranteed not to be zero.
/// </summary>
public static long UniformLongNonZero(this IRandomUniform rnd)
{
long r;
do
{
r = rnd.UniformLong();
} while (r == 0);
return(r);
}
/// <summary>
/// Creates an unordered array of subsetCount long indices that
/// constitute a subset of all longs in the range [0, count-1].
/// O(subsetCount) for subsetCount << count.
/// NOTE: It is assumed that subsetCount is significantly smaller
/// than count. If this is not the case, use
/// CreateRandomSubsetOfSize instead.
/// WARNING: As subsetCount approaches count execution time
/// increases significantly.
/// </summary>
public static long[] CreateSmallRandomSubsetIndexArrayLong(
this IRandomUniform rnd, long subsetCount, long count)
{
Requires.That(subsetCount >= 0 && subsetCount <= count);
var subsetIndices = new LongSet(subsetCount);
for (int i = 0; i < subsetCount; i++)
{
long index;
do
{
index = rnd.UniformLong(count);
}while (!subsetIndices.TryAdd(index));
}
return(subsetIndices.ToArray());
}
/// <summary>
/// Randomly permute the first count elements of the
/// supplied array. This does work with counts of up
/// to about 2^50.
/// </summary>
public static void Randomize <T>(
this IRandomUniform rnd, T[] array, long count)
{
if (count <= (long)int.MaxValue)
{
int intCount = (int)count;
for (int i = 0; i < intCount; i++)
{
array.Swap(i, rnd.UniformInt(intCount));
}
}
else
{
for (long i = 0; i < count; i++)
{
array.Swap(i, rnd.UniformLong(count));
}
}
}
/// <summary>
/// Creates an unordered array of subsetCount long indices that
/// constitute a subset of all longs in the range [0, count-1].
/// O(subsetCount) for subsetCount << count.
/// NOTE: It is assumed that subsetCount is significantly smaller
/// than count. If this is not the case, use
/// CreateRandomSubsetOfSize instead.
/// WARNING: As subsetCount approaches count execution time
/// increases significantly.
/// </summary>
public static long[] CreateSmallRandomSubsetIndexArrayLong(
this IRandomUniform rnd, long subsetCount, long count)
{
if (!(subsetCount >= 0 && subsetCount <= count))
{
throw new ArgumentOutOfRangeException(nameof(subsetCount));
}
var subsetIndices = new LongSet(subsetCount);
for (int i = 0; i < subsetCount; i++)
{
long index;
do
{
index = rnd.UniformLong(count);
}while (!subsetIndices.TryAdd(index));
}
return(subsetIndices.ToArray());
}
