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//---------------------------------------------------------------------
// <copyright file="ConversionContext.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//
// @owner Microsoft
// @backupOwner Microsoft
//---------------------------------------------------------------------
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
namespace System.Data.Common.Utils.Boolean
{
/// <summary>
/// Manages state used to translate BoolExpr to decision diagram vertices and back again.
/// Specializations exist for generic and DomainConstraint expressions.
/// </summary>
internal abstract class ConversionContext<T_Identifier>
{
/// <summary>
/// Gets the solver instance associated with this conversion context. Used to reterieve
/// canonical Decision Diagram vertices for this context.
/// </summary>
internal readonly Solver Solver = new Solver();
/// <summary>
/// Given a term in BoolExpr, returns the corresponding decision diagram vertex.
/// </summary>
internal abstract Vertex TranslateTermToVertex(TermExpr<T_Identifier> term);
/// <summary>
/// Describes a vertex as a series of literal->vertex successors such that the literal
/// logically implies the given vertex successor.
/// </summary>
internal abstract IEnumerable<LiteralVertexPair<T_Identifier>> GetSuccessors(Vertex vertex);
}
/// <summary>
/// VertexLiteral pair, used for ConversionContext.GetSuccessors
/// </summary>
internal sealed class LiteralVertexPair<T_Identifier>
{
internal readonly Vertex Vertex;
internal readonly Literal<T_Identifier> Literal;
internal LiteralVertexPair(Vertex vertex, Literal<T_Identifier> literal)
{
this.Vertex = vertex;
this.Literal = literal;
}
}
/// <summary>
/// Generic implementation of a ConversionContext
/// </summary>
internal sealed class GenericConversionContext<T_Identifier> : ConversionContext<T_Identifier>
{
readonly Dictionary<TermExpr<T_Identifier>, int> _variableMap = new Dictionary<TermExpr<T_Identifier>, int>();
Dictionary<int, TermExpr<T_Identifier>> _inverseVariableMap;
internal override Vertex TranslateTermToVertex(TermExpr<T_Identifier> term)
{
int variable;
if (!_variableMap.TryGetValue(term, out variable))
{
variable = Solver.CreateVariable();
_variableMap.Add(term, variable);
}
return Solver.CreateLeafVertex(variable, Solver.BooleanVariableChildren);
}
internal override IEnumerable<LiteralVertexPair<T_Identifier>> GetSuccessors(Vertex vertex)
{
LiteralVertexPair<T_Identifier>[] successors = new LiteralVertexPair<T_Identifier>[2];
Debug.Assert(2 == vertex.Children.Length);
Vertex then = vertex.Children[0];
Vertex @else = vertex.Children[1];
// get corresponding term expression
InitializeInverseVariableMap();
TermExpr<T_Identifier> term = _inverseVariableMap[vertex.Variable];
// add positive successor (then)
Literal<T_Identifier> literal = new Literal<T_Identifier>(term, true);
successors[0] = new LiteralVertexPair<T_Identifier>(then, literal);
// add negative successor (else)
literal = literal.MakeNegated();
successors[1] = new LiteralVertexPair<T_Identifier>(@else, literal);
return successors;
}
private void InitializeInverseVariableMap()
{
if (null == _inverseVariableMap)
{
_inverseVariableMap = _variableMap.ToDictionary(kvp => kvp.Value, kvp => kvp.Key);
}
}
}
/// <summary>
/// Specialization of ConversionContext for DomainConstraint BoolExpr
/// </summary>
internal sealed class DomainConstraintConversionContext<T_Variable, T_Element> : ConversionContext<DomainConstraint<T_Variable, T_Element>>
{
/// <summary>
/// A map from domain variables to decision diagram variables.
/// </summary>
readonly Dictionary<DomainVariable<T_Variable, T_Element>, int> _domainVariableToRobddVariableMap =
new Dictionary<DomainVariable<T_Variable, T_Element>, int>();
Dictionary<int, DomainVariable<T_Variable, T_Element>> _inverseMap;
/// <summary>
/// Translates a domain constraint term to an N-ary DD vertex.
/// </summary>
internal override Vertex TranslateTermToVertex(TermExpr<DomainConstraint<T_Variable, T_Element>> term)
{
var range = term.Identifier.Range;
var domainVariable = term.Identifier.Variable;
var domain = domainVariable.Domain;
if (range.All(element => !domain.Contains(element)))
{
// trivially false
return Vertex.Zero;
}
if (domain.All(element => range.Contains(element)))
{
// trivially true
return Vertex.One;
}
// determine assignments for this constraints (if the range contains a value in the domain, '1', else '0')
Vertex[] children = domain.Select(element => range.Contains(element) ? Vertex.One : Vertex.Zero).ToArray();
// see if we know this variable
int robddVariable;
if (!_domainVariableToRobddVariableMap.TryGetValue(domainVariable, out robddVariable))
{
robddVariable = Solver.CreateVariable();
_domainVariableToRobddVariableMap[domainVariable] = robddVariable;
}
// create a new vertex with the given assignments
return Solver.CreateLeafVertex(robddVariable, children);
}
internal override IEnumerable<LiteralVertexPair<DomainConstraint<T_Variable, T_Element>>> GetSuccessors(Vertex vertex)
{
InitializeInverseMap();
var domainVariable = _inverseMap[vertex.Variable];
// since vertex children are ordinally aligned with domain, handle domain as array
var domain = domainVariable.Domain.ToArray();
// foreach unique successor vertex, build up range
Dictionary<Vertex, Set<T_Element>> vertexToRange = new Dictionary<Vertex, Set<T_Element>>();
for (int i = 0; i < vertex.Children.Length; i++)
{
Vertex successorVertex = vertex.Children[i];
Set<T_Element> range;
if (!vertexToRange.TryGetValue(successorVertex, out range))
{
range = new Set<T_Element>(domainVariable.Domain.Comparer);
vertexToRange.Add(successorVertex, range);
}
range.Add(domain[i]);
}
foreach (var vertexRange in vertexToRange)
{
var successorVertex = vertexRange.Key;
var range = vertexRange.Value;
// construct a DomainConstraint including the given range
var constraint = new DomainConstraint<T_Variable, T_Element>(domainVariable, range.MakeReadOnly());
var literal = new Literal<DomainConstraint<T_Variable, T_Element>>(
new TermExpr<DomainConstraint<T_Variable, T_Element>>(constraint), true);
yield return new LiteralVertexPair<DomainConstraint<T_Variable, T_Element>>(successorVertex, literal);
}
}
private void InitializeInverseMap()
{
if (null == _inverseMap)
{
_inverseMap = _domainVariableToRobddVariableMap.ToDictionary(kvp => kvp.Value, kvp => kvp.Key);
}
}
}
}
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