/// <summary>
/// Get a nondet choice.
/// This may replay a nondet choice or make (and record) a new nondet choice.
/// </summary>
/// <param name="isBoolChoice">If true, a boolean choice; otherwise, an int choice.</param>
/// <param name="rand">Random</param>
/// <param name="contract">IContract</param>
public int MakeOrReplayNondetChoice(bool isBoolChoice, IRandomNumberGenerator rand, IContract contract)
{
contract.Assert(
rand != null || isBoolChoice,
"A DFS DPOR exploration of int nondeterminstic choices " +
"is not currently supported because this won't scale.");
if (NondetChoices == null)
{
NondetChoices = new List <NonDetChoice>();
}
if (NextNondetChoiceIndex < NondetChoices.Count)
{
// Replay:
NonDetChoice choice = NondetChoices[NextNondetChoiceIndex];
++NextNondetChoiceIndex;
contract.Assert(choice.IsBoolChoice == isBoolChoice);
return(choice.Choice);
}
// Adding a choice.
contract.Assert(NextNondetChoiceIndex == NondetChoices.Count);
NonDetChoice ndc = new NonDetChoice
{
IsBoolChoice = isBoolChoice,
Choice = rand == null ? 0 : (isBoolChoice ? rand.Next(2) : rand.Next())
};
NondetChoices.Add(ndc);
++NextNondetChoiceIndex;
return(ndc.Choice);
}
/// <summary>
/// This method is used in a DFS exploration of nondet choice.
/// It will pop off bool choices that are 1 until
/// it reaches a 0 that will then be changed to a 1.
/// The NextNondetChoiceIndex will be reset ready for replay.
/// </summary>
/// <param name="contract">IContract</param>
/// <returns>false if there are no more nondet choices to explore</returns>
public bool BacktrackNondetChoices(IContract contract)
{
if (NondetChoices == null)
{
return(false);
}
contract.Assert(NextNondetChoiceIndex == NondetChoices.Count);
NextNondetChoiceIndex = 0;
while (NondetChoices.Count > 0)
{
NonDetChoice choice = NondetChoices[NondetChoices.Count - 1];
contract.Assert(choice.IsBoolChoice, "DFS DPOR only supports bool choices.");
if (choice.Choice == 0)
{
choice.Choice = 1;
NondetChoices[NondetChoices.Count - 1] = choice;
return(true);
}
contract.Assert(choice.Choice == 1, "Unexpected choice value.");
NondetChoices.RemoveAt(NondetChoices.Count - 1);
}
return(false);
}
