/// <summary>
/// used by random table generators to select random number of columns and rows. This method will return very low numbers with high probability,
/// </summary>
public void NextTableDimentions(int maxRows, int maxColumns, int maxTotalSize, out int randRows, out int randColumns)
{
// prefer really low values to ensure table size will not go up way too much too frequently
const LowValueEnforcementLevel level = LowValueEnforcementLevel.Medium;
if (NextBit())
{
// select rows first, then columns
randColumns = NextAllocationUnit(1, maxColumns, level);
randRows = NextAllocationUnit(1, Math.Min(maxRows, maxTotalSize / randColumns), level);
}
else
{
randRows = NextAllocationUnit(1, maxRows, level);
randColumns = NextAllocationUnit(1, Math.Min(maxColumns, maxTotalSize / randRows), level);
}
}
/// <summary>
/// generates size value with low probability of large size values within the given range
/// </summary>
/// <param name="lowValuesEnforcementLevel">
/// lowValuesEnforcementLevel is value between 0 and 31;
/// 0 means uniform distribution in the min/max range;
/// 31 means very low chances for high values
/// </param>
private int NextAllocationUnit(int minSize, int maxSize, LowValueEnforcementLevel lowValuesLevel)
{
if (minSize < 0 || maxSize < 0 || minSize > maxSize)
{
throw new ArgumentOutOfRangeException("minSize or maxSize are out of range");
}
if (lowValuesLevel < LowValueEnforcementLevel.VeryStrong || lowValuesLevel > LowValueEnforcementLevel.Uniform)
{
throw new ArgumentOutOfRangeException("lowValuesLevel");
}
if (minSize == maxSize)
{
return(minSize); // shortcut for fixed size
}
long longRange = (long)maxSize - (long)minSize + 1;
// create a sample in range [0, 1) (it is never 1)
double sample = base.NextDouble();
// decrease chances of large size values based on the how many bits digits are set in the maxValue
int bitsPerLevel = (int)lowValuesLevel;
long maxBitsLeft = longRange >> bitsPerLevel;
while (maxBitsLeft > 0)
{
sample *= base.NextDouble();
maxBitsLeft >>= bitsPerLevel;
}
int res = minSize + (int)(sample * longRange);
Debug.Assert(res >= minSize && res <= maxSize);
return(res);
}
