/// <summary>
/// Uses the frame to simplify Constraints. See section 3.3.1.2 of Cousot and Halbwachs.
///
/// Note: This code does not necessarily eliminate all irrelevant equalities; Cousot and
/// Halbwachs only claim that the technique eliminates all irrelevant inequalities.
/// </summary>
void SimplifyConstraints() {
if (Constraints == null) {
return;
}
Contract.Assume(this.FrameVertices != null);
Contract.Assume(this.FrameRays != null);
SimplificationStatus[] status = new SimplificationStatus[Constraints.Count];
/*readonly*/
int feCount = FrameVertices.Count + FrameRays.Count;
// Create a table that keeps track of which constraints are satisfied by which vertices and rays
bool[,] sat = new bool[Constraints.Count, FrameVertices.Count + FrameRays.Count];
for (int i = 0; i < Constraints.Count; i++) {
status[i] = SimplificationStatus.Relevant;
LinearConstraint lc = (LinearConstraint/*!*/)cce.NonNull(Constraints[i]);
int cnt = 0; // number of vertices and rays that saturate lc
for (int j = 0; j < FrameVertices.Count; j++) {
FrameElement vertex = (FrameElement/*!*/)cce.NonNull(FrameVertices[j]);
if (lc.IsSaturatedBy(vertex, true)) {
sat[i, j] = true;
cnt++;
}
}
if (cnt == 0) {
// no vertex saturates the constraint, so the constraint is irrelevant
status[i] = SimplificationStatus.Irrelevant;
continue;
}
for (int j = 0; j < FrameRays.Count; j++) {
FrameElement ray = (FrameElement/*!*/)cce.NonNull(FrameRays[j]);
if (lc.IsSaturatedBy(ray, false)) {
sat[i, FrameVertices.Count + j] = true;
cnt++;
}
}
if (cnt == feCount) {
status[i] = SimplificationStatus.More;
} else {
// Cousot and Halbwachs says that all equalities are found in the way we just tested.
// If I understand that right, then we should not get here if the constraint is an
// equality constraint. The following assertion tests my understanding. --KRML
System.Diagnostics.Debug.Assert(lc.Relation == LinearConstraint.ConstraintRelation.LE);
}
}
CheckPairSimplifications(sat, status);
// Finally, make the changes to the list of constraints
for (int i = Constraints.Count - 1; 0 <= i; i--) {
switch (status[i]) {
case SimplificationStatus.Relevant:
break;
case SimplificationStatus.Irrelevant:
#if DEBUG_PRINT
Console.WriteLine("Removing irrelevant constraint: {0}", Constraints[i]);
#endif
Constraints.RemoveAt(i);
break;
case SimplificationStatus.More:
LinearConstraint lc = (LinearConstraint/*!*/)cce.NonNull(Constraints[i]);
if (lc.Relation == LinearConstraint.ConstraintRelation.LE) {
#if DEBUG_PRINT
Console.WriteLine("Converting the following constraint into an equality: {0}", lc);
#endif
LinearConstraint lcEq = lc.ChangeRelation(LinearConstraint.ConstraintRelation.EQ);
Constraints[i] = lcEq;
}
break;
}
}
foreach (LinearConstraint/*!*/ lc in Constraints) {
Contract.Assert(lc != null);
lc.Normalize();
}
}
/// <summary>
/// Requires sat.GetLength(0) == status.Length.
/// </summary>
/// <param name="sat"></param>
/// <param name="status"></param>
static void CheckPairSimplifications(bool[,]/*!*/ sat, SimplificationStatus[]/*!*/ status) {
Contract.Requires(status != null);
Contract.Requires(sat != null);
Contract.Requires(sat.GetLength(0) == status.Length);
int M = sat.GetLength(0);
int N = sat.GetLength(1);
for (int i = 0; i < M - 1; i++) {
if (status[i] != SimplificationStatus.Relevant) {
continue;
}
for (int j = i + 1; j < M; j++) {
if (status[j] != SimplificationStatus.Relevant) {
continue;
}
// check (sat[i,*] <= sat[j,*]) and (sat[i,*] >= sat[j,*])
int cmp = 0; // -1: (sat[i,*] <= sat[j,*]), 0: equal, 1: (sat[i,*] >= sat[j,*])
for (int c = 0; c < N; c++) {
if (cmp < 0) {
if (sat[i, c] && !sat[j, c]) {
// incomparable
goto NEXT_PAIR;
}
} else if (0 < cmp) {
if (!sat[i, c] && sat[j, c]) {
// incomparable
goto NEXT_PAIR;
}
} else if (sat[i, c] != sat[j, c]) {
if (!sat[i, c]) {
cmp = -1;
} else {
cmp = 1;
}
}
}
if (cmp <= 0) {
// sat[i,*] <= sat[j,*] holds, so mark i as irrelevant
status[i] = SimplificationStatus.Irrelevant;
goto NEXT_OUTER;
} else {
// sat[i,*] >= sat[j,*] holds, so mark j as irrelevant
status[j] = SimplificationStatus.Irrelevant;
}
NEXT_PAIR: {
}
}
NEXT_OUTER: {
}
}
}
static void RemoveIrrelevantFrameElements(ArrayList/*!*/ /*FrameElement*/ ff, SimplificationStatus[]/*!*/ status,
/*maybe null*/ ArrayList /*FrameElement*/ lines) {
Contract.Requires(ff != null);
Contract.Requires(status != null);
Contract.Requires(ff.Count == status.Length);
for (int j = ff.Count - 1; 0 <= j; j--) {
switch (status[j]) {
case SimplificationStatus.Relevant:
break;
case SimplificationStatus.Irrelevant:
#if DEBUG_PRINT
Console.WriteLine("Removing irrelevant {0}: {1}", lines == null ? "vertex" : "ray", ff[j]);
#endif
ff.RemoveAt(j);
break;
case SimplificationStatus.More:
System.Diagnostics.Debug.Assert(lines != null);
FrameElement f = (FrameElement)ff[j];
#if DEBUG_PRINT
Console.WriteLine("Changing ray into line: {0}", f);
#endif
ff.RemoveAt(j);
Contract.Assert(lines != null);
lines.Add(f);
break;
}
}
}
/// <summary>
/// For each i, sets status[i] to:
/// <ul>
/// <li>Irrelevant if ff[i] is irrelevant</li>
/// <li>Relevant if ff[i] is irrelevant</li>
/// <li>More if vertices is true and ray ff[i] can be replaced by a line ff[i]</li>
/// </ul>
/// </summary>
/// <param name="ff"></param>
/// <param name="vertices">true if "ff" contains vertices; false if "ff" contains rays</param>
/// <param name="constraints"></param>
/// <param name="status"></param>
static void SimplifyFrameElements(ArrayList/*!*/ /*FrameElement*/ ff, bool vertices, ArrayList/*!*/ /*LinearConstraint*/ constraints, out SimplificationStatus[]/*!*/ status) {
Contract.Requires(ff != null);
Contract.Requires(constraints != null);
Contract.Ensures(Contract.ValueAtReturn(out status) != null);
status = new SimplificationStatus[ff.Count];
bool[,] sat = new bool[ff.Count, constraints.Count];
for (int i = 0; i < ff.Count; i++) {
FrameElement f = (FrameElement/*!*/)cce.NonNull(ff[i]);
int cnt = 0;
for (int c = 0; c < constraints.Count; c++) {
LinearConstraint lc = (LinearConstraint/*!*/)cce.NonNull(constraints[c]);
bool s = lc.IsSaturatedBy(f, vertices);
if (s) {
sat[i, c] = true;
cnt++;
}
}
if (!vertices && cnt == constraints.Count) {
status[i] = SimplificationStatus.More;
} else {
status[i] = SimplificationStatus.Relevant;
}
}
CheckPairSimplifications(sat, status);
}
