ni_nitdoc: added fast copy past utility to signatures.

[nit.git] / src / layout_builders.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Table layout builders
# Tables are used to implement objects mecanisms like:
#   * message sending
#       * attribute accessing
#       * typing
#       * resolution (for generic types)
# This module provides various layout for object tables:
#       * coloring
#       * binary matrix
#       * perfect hashing (and & mod operators)
module layout_builders

import abstract_compiler

# Layouts

# A layout is the result of computation by builders
# it contains necessary informations for basic table creation
class Layout[E: Object]
        # Ids or each element
        var ids: Map[E, Int] = new HashMap[E, Int]
        # Fixed positions of each element in all tables
        var pos: Map[E, Int] = new HashMap[E, Int]
end

# A PHLayout is used everywere the builder used perfect hashing
# it adds masks and hashes informations to std layout
class PHLayout[HOLDER: Object, E: Object]
        super Layout[E]
        # Masks used by hash function
        var masks: Map[HOLDER, Int] = new HashMap[HOLDER, Int]
        # Positions of each element for each tables
        var hashes: Map[HOLDER, Map[E, Int]] = new HashMap[HOLDER, Map[E, Int]]
end

# Builders

# TypingLayoutBuilder is used to build a layout for typing tables (by type or by class)
interface TypingLayoutBuilder[E: Object]
        # Build typing table layout
        # elements: the set of elements (classes or types) used in typing tables
        fun build_layout(elements: Set[E]): Layout[E] is abstract
end

# Layout builder dedicated to vft, attribute & VT tables
interface PropertyLayoutBuilder[E: MProperty]
        # Build table layout for attributes, methods and virtual types
        # elements: the set of classes containing the properties to use in table layout
        fun build_layout(elements: Set[MClass]): Layout[E] is abstract
end

# For resolution tables (generics)
interface ResolutionLayoutBuilder
        # Build resolution table layout
        # elements: association between classes and resolved types
        fun build_layout(elements: Map[MClassType, Set[MType]]): Layout[MType] is abstract
end

# Matrice computers

# Abstract layout builder for resolution tables using Binary Matrix (BM)
abstract class TypingBMizer[E: Object]
        super TypingLayoutBuilder[E]

        var mmodule: MModule

        init(mmodule: MModule) do
                self.mmodule = mmodule
        end

        # Compute mtypes ids and position using BM
        redef fun build_layout(elements: Set[E]): Layout[E] do
                var result = new Layout[E]
                var ids = new HashMap[E, Int]
                var lin = self.reverse_linearize(elements)
                for element in lin do
                        ids[element] = ids.length
                end
                result.ids = ids
                result.pos = ids
                return result
        end

        private fun reverse_linearize(elements: Set[E]): Array[E] is abstract
end

# Layout builder for typing tables based on classes using Binary Matrix (BM)
class MTypeBMizer
        super TypingBMizer[MType]

        init(mmodule: MModule) do super(mmodule)

        redef fun reverse_linearize(elements) do
                return self.mmodule.reverse_linearize_mtypes(elements)
        end
end

# Layout builder for typing tables based on types using Binary Matrix (BM)
class MClassBMizer
        super TypingBMizer[MClass]

        init(mmodule: MModule) do super(mmodule)

        redef fun reverse_linearize(elements) do
                return self.mmodule.reverse_linearize_mclasses(elements)
        end
end

# Layout builder for resolution tables using Binary Matrix (BM)
class ResolutionBMizer
        super ResolutionLayoutBuilder

        init do end

        redef fun build_layout(elements) do
                var result = new Layout[MType]
                var ids = new HashMap[MType, Int]
                var color = 0
                for mclasstype, mclasstypes in elements do
                        for element in mclasstypes do
                                if ids.has_key(element) then continue
                                ids[element] = color
                                color += 1
                        end
                end
                result.ids = ids
                result.pos = ids
                return result
        end
end

# Abstract Layout builder for mproperties using Binary Matrix (BM)
abstract class MPropertyBMizer[E: MProperty]
        super PropertyLayoutBuilder[E]

        type MPROP: MProperty

        var mmodule: MModule

        init(mmodule: MModule) do self.mmodule = mmodule

        redef fun build_layout(elements) do
                var result = new Layout[E]
                var ids = new HashMap[E, Int]
                var lin = linearize_mclasses(elements)
                for mclass in lin do
                        for mproperty in properties(mclass) do
                                if ids.has_key(mproperty) then continue
                                ids[mproperty] = ids.length
                        end
                end
                result.pos = ids
                return result
        end

        # extract properties of a mclass
        private fun properties(mclass: MClass): Set[E] do
                var properties = new HashSet[E]
                for mprop in self.mmodule.properties(mclass) do
                        if mprop isa MPROP then properties.add(mprop)
                end
                return properties
        end

        private fun linearize_mclasses(mclasses: Set[MClass]): Array[MClass] is abstract
end

# Layout builder for vft using Binary Matrix (BM)
class MMethodBMizer
        super MPropertyBMizer[MMethod]

        redef type MPROP: MMethod
        init(mmodule: MModule) do super(mmodule)
        # Less holes in tables with reverse linearization for method tables
        redef fun linearize_mclasses(mclasses) do return self.mmodule.reverse_linearize_mclasses(mclasses)
end

# Layout builder for attribute tables using Binary Matrix (BM)
class MAttributeBMizer
        super MPropertyBMizer[MAttribute]

        redef type MPROP: MAttribute
        init(mmodule: MModule) do super(mmodule)
        # Less holes in tables with linearization for attribute tables
        redef fun linearize_mclasses(mclasses) do return self.mmodule.linearize_mclasses_2(mclasses)
end

# BMizing for MVirtualTypeProps
class MVirtualTypePropBMizer
        super MPropertyBMizer[MVirtualTypeProp]

        redef type MPROP: MVirtualTypeProp
        init(mmodule: MModule) do super(mmodule)
        # Less holes in tables with reverse linearization for method tables
        redef fun linearize_mclasses(mclasses) do return self.mmodule.reverse_linearize_mclasses(mclasses)
end

# Colorers

# Abstract Layout builder for typing table using coloration (CL)
abstract class TypingColorer[E: Object]
        super TypingLayoutBuilder[E]

        private var core: Set[E] = new HashSet[E]
        private var crown: Set[E] = new HashSet[E]
        private var border: Set[E] = new HashSet[E]

        private var coloration_result: Map[E, Int] = new HashMap[E, Int]

        init do end

        # Compute the layout with coloring
        redef fun build_layout(elements: Set[E]): Layout[E] do
                var result = new Layout[E]
                result.ids = compute_ids(elements)
                result.pos = colorize(elements)
                return result
        end

        private fun compute_ids(elements: Set[E]): Map[E, Int] do
                var ids = new HashMap[E, Int]
                var lin = reverse_linearize(elements)
                for element in lin do
                        ids[element] = ids.length
                end
                return ids
        end

        private fun colorize(elements: Set[E]): Map[E, Int] do
                tag_elements(elements)
                build_conflicts_graph(elements)
                colorize_elements(core)
                colorize_elements(border)
                colorize_elements(crown)
                return coloration_result
        end

        # Colorize a collection of elements
        private fun colorize_elements(elements: Set[E]) do
                var min_color = 0

                var lin = reverse_linearize(elements)
                for element in lin do
                        var color = min_color
                        while not self.is_color_free(element, elements, color) do
                                color += 1
                        end
                        coloration_result[element] = color
                        color = min_color
                end
        end

        # Check if a related element to the element already use the color
        private fun is_color_free(element: E, elements: Set[E], color: Int): Bool do
                if conflicts_graph.has_key(element) then
                        for st in conflicts_graph[element] do
                                if coloration_result.has_key(st) and coloration_result[st] == color then return false
                        end
                end
                for st in self.super_elements(element, elements) do
                        if coloration_result.has_key(st) and coloration_result[st] == color then return false
                end
                return true
        end

        # Tag elements as core, crown or border
        private fun tag_elements(elements: Set[E]) do
                for element in elements do
                        # Check if sub elements are all in single inheritance
                        var all_subelements_si = true
                        for subelem in self.sub_elements(element, elements) do
                                if self.is_element_mi(subelem, elements) then
                                        all_subelements_si = false
                                        break
                                end
                        end

                        # Tag as core, crown or border
                        if self.is_element_mi(element, elements) then
                                core.add_all(self.super_elements(element, elements))
                                core.add(element)
                                if all_subelements_si then
                                        border.add(element)
                                end
                        else if not all_subelements_si then
                                core.add_all(self.super_elements(element, elements))
                                core.add(element)
                        else
                                crown.add(element)
                        end
                end
        end

        # Conflicts graph of elements hierarchy (two types are in conflict if they have common subelements)
        private fun build_conflicts_graph(elements: Set[E]) do
                self.conflicts_graph = new HashMap[E, HashSet[E]]
                var core = reverse_linearize(self.core)
                for t in core do
                        for i in self.linear_extension(t, elements) do
                                if t == i then continue

                                var lin_i = self.linear_extension(i, elements)

                                for j in self.linear_extension(t, elements) do
                                        if i == j or j == t then continue
                                        var lin_j = self.linear_extension(j, elements)

                                        var d_ij = lin_i - lin_j
                                        var d_ji = lin_j - lin_i

                                        for ed1 in d_ij do
                                                if not conflicts_graph.has_key(ed1) then conflicts_graph[ed1] = new HashSet[E]
                                                # add ed1 x ed2 to conflicts graph
                                                for ed2 in d_ji do conflicts_graph[ed1].add(ed2)
                                        end
                                        for ed1 in d_ij do
                                                if not conflicts_graph.has_key(ed1) then conflicts_graph[ed1] = new HashSet[E]
                                                # add ed1 x ed2 to conflicts graph
                                                for ed2 in d_ji do conflicts_graph[ed1].add(ed2)
                                        end
                                end
                        end
                end
        end

        private var conflicts_graph: nullable HashMap[E, Set[E]]

        # cache for linear_extensions
        private var linear_extensions_cache: Map[E, Array[E]] = new HashMap[E, Array[E]]

        # Return a linear_extension of super_elements of the element
        private fun linear_extension(element: E, elements: Set[E]): Array[E] do
                if not self.linear_extensions_cache.has_key(element) then
                        var supers = new HashSet[E]
                        supers.add(element)
                        supers.add_all(self.super_elements(element, elements))
                        self.linear_extensions_cache[element] = self.linearize(supers)
                end
                return self.linear_extensions_cache[element]
        end

        private fun super_elements(element: E, elements: Set[E]): Set[E] is abstract
        private fun sub_elements(element: E, elements: Set[E]): Set[E] is abstract
        private fun is_element_mi(element: E, elements: Set[E]): Bool is abstract
        private fun linearize(elements: Set[E]): Array[E] is abstract
        private fun reverse_linearize(elements: Set[E]): Array[E] is abstract
end

# Layout builder for typing tables based on types using coloration (CL)
class MTypeColorer
        super TypingColorer[MType]

        var mmodule: MModule

        init(mmodule: MModule) do self.mmodule = mmodule

        redef fun super_elements(element, elements) do return self.mmodule.super_mtypes(element, elements)
        redef fun is_element_mi(element, elements) do return self.super_elements(element, elements).length > 1
        redef fun sub_elements(element, elements) do do return self.mmodule.sub_mtypes(element, elements)
        redef fun linearize(elements) do return self.mmodule.linearize_mtypes(elements)
        redef fun reverse_linearize(elements) do return self.mmodule.reverse_linearize_mtypes(elements)
end

# Layout builder for typing tables based on classes using coloration (CL)
class MClassColorer
        super TypingColorer[MClass]

        private var mmodule: MModule

        init(mmodule: MModule) do self.mmodule = mmodule

        redef fun super_elements(element, elements) do return self.mmodule.super_mclasses(element)
        fun parent_elements(element: MClass): Set[MClass] do return self.mmodule.parent_mclasses(element)
        redef fun is_element_mi(element, elements) do return self.parent_elements(element).length > 1
        redef fun sub_elements(element, elements) do do return self.mmodule.sub_mclasses(element)
        redef fun linearize(elements) do return self.mmodule.linearize_mclasses_2(elements)
        redef fun reverse_linearize(elements) do return self.mmodule.reverse_linearize_mclasses(elements)
end

# Abstract Layout builder for properties tables using coloration (CL)
abstract class MPropertyColorer[E: MProperty]
        super PropertyLayoutBuilder[E]

        type MPROP: MProperty

        private var mmodule: MModule
        private var class_colorer: MClassColorer
        private var coloration_result: Map[E, Int] = new HashMap[E, Int]

        init(mmodule: MModule) do
                self.mmodule = mmodule
                self.class_colorer = new MClassColorer(mmodule)
        end

        # Compute mclasses ids and position using BM
        redef fun build_layout(mclasses: Set[MClass]): Layout[E] do
                var result = new Layout[E]
                result.pos = self.colorize(mclasses)
                return result
        end

        private fun colorize(mclasses: Set[MClass]): Map[E, Int] do
                self.class_colorer.tag_elements(mclasses)
                self.class_colorer.build_conflicts_graph(mclasses)
                self.colorize_core(self.class_colorer.core)
                self.colorize_crown(self.class_colorer.crown)
                return self.coloration_result
        end

        # Colorize properties of the core hierarchy
        private fun colorize_core(mclasses: Set[MClass]) do
                var min_color = 0
                for mclass in mclasses do
                        var color = min_color

                        # if the class is root, get the minimal color
                        if self.mmodule.parent_mclasses(mclass).length == 0 then
                                colorize_elements(self.properties(mclass), color)
                        else
                                # check last color used by parents
                                color = max_color(color, self.mmodule.parent_mclasses(mclass))
                                # check max color used in conflicts
                                if self.class_colorer.conflicts_graph.has_key(mclass) then
                                        color = max_color(color, self.class_colorer.conflicts_graph[mclass])
                                end
                                colorize_elements(self.properties(mclass), color)
                        end
                end
        end

        # Colorize properties of the crown hierarchy
        private fun colorize_crown(mclasses: Set[MClass]) do
                for mclass in mclasses do
                        colorize_elements(self.properties(mclass), max_color(0, self.mmodule.parent_mclasses(mclass)))
                end
        end

        # Colorize a collection of mproperties given a starting color
        private fun colorize_elements(elements: Collection[E], start_color: Int) do
                for element in elements do
                        if self.coloration_result.has_key(element) then continue
                        self.coloration_result[element] = start_color
                        start_color += 1
                end
        end

        private fun max_color(min_color: Int, mclasses: Collection[MClass]): Int do
                var max_color = min_color

                for mclass in mclasses do
                        for mproperty in self.properties(mclass) do
                                var color = min_color
                                if self.coloration_result.has_key(mproperty) then
                                        color = self.coloration_result[mproperty]
                                        if color >= max_color then max_color = color + 1
                                end
                        end
                end
                return max_color
        end

        # Filter properties
        private fun properties(mclass: MClass): Set[E] do
                var properties = new HashSet[E]
                for mprop in self.mmodule.properties(mclass) do
                        if mprop isa MPROP then properties.add(mprop)
                end
                return properties
        end
end

# Layout builder for vft using coloration (CL)
class MMethodColorer
        super MPropertyColorer[MMethod]

        redef type MPROP: MMethod
        init(mmodule: MModule) do super
end

# Layout builder for attributes using coloration (CL)
class MAttributeColorer
        super MPropertyColorer[MAttribute]

        redef type MPROP: MAttribute
        init(mmodule: MModule) do super
end

# Layout builder for virtual types using coloration (CL)
class MVirtualTypePropColorer
        super MPropertyColorer[MVirtualTypeProp]

        redef type MPROP: MVirtualTypeProp
        init(mmodule: MModule) do super
end

# Layout builder for resolution tables using coloration (CL)
class ResolutionColorer
        super ResolutionLayoutBuilder

        private var coloration_result: Map[MType, Int] = new HashMap[MType, Int]

        init do end

        # Compute resolved types colors
        redef fun build_layout(elements) do
                self.build_conflicts_graph(elements)
                var result = new Layout[MType]
                result.ids = self.compute_ids(elements)
                result.pos = self.colorize_elements(elements)
                return result
        end

        private fun compute_ids(elements: Map[MClassType, Set[MType]]): Map[MType, Int] do
                var ids = new HashMap[MType, Int]
                var color = 0
                for mclasstype, mclasstypes in elements do
                        for element in mclasstypes do
                                if ids.has_key(element) then continue
                                ids[element] = color
                                color += 1
                        end
                end
                return ids
        end

        # Colorize a collection of elements
        private fun colorize_elements(elements: Map[MClassType, Set[MType]]): Map[MType, Int] do
                var min_color = 0
                for mclasstype, mclasstypes in elements do
                        for element in mclasstypes do
                                if self.coloration_result.has_key(element) then continue
                                var color = min_color
                                while not self.is_color_free(element, color) do
                                        color += 1
                                end
                                coloration_result[element] = color
                                color = min_color
                        end
                end
                return self.coloration_result
        end

        # Check if a related element to the element already use the color
        private fun is_color_free(element: MType, color: Int): Bool do
                if conflicts_graph.has_key(element) then
                        for st in conflicts_graph[element] do
                                if coloration_result.has_key(st) and coloration_result[st] == color then return false
                        end
                end
                return true
        end

        # look for unanchored types generated by the same type
        private fun build_conflicts_graph(elements: Map[MClassType, Set[MType]]) do
                for mclasstype, mtypes in elements do
                        for mtype in mtypes do
                                for otype in mtypes do
                                        if otype == mtype then continue
                                        self.add_conflict(mtype, otype)
                                end
                        end
                end
        end

        private var conflicts_graph: Map[MType, Set[MType]] = new HashMap[MType, Set[MType]]

        private fun add_conflict(mtype: MType, otype: MType) do
                if mtype == otype then return
                if not self.conflicts_graph.has_key(mtype) then  self.conflicts_graph[mtype] = new HashSet[MType]
                self.conflicts_graph[mtype].add(otype)
                if not self.conflicts_graph.has_key(otype) then  self.conflicts_graph[otype] = new HashSet[MType]
                self.conflicts_graph[otype].add(mtype)
        end
end

# Perfect Hashing (PH)
# T = type of holder
# U = type of elements to hash
private class PerfectHasher[T: Object, U: Object]

        var operator: PHOperator

        init(operator: PHOperator) do self.operator = operator

        # Compute mask for each holders
        fun compute_masks(conflicts: Map[T, Set[U]], ids: Map[U, Int]): Map[T, Int] do
                var masks = new HashMap[T, Int]
                for mclasstype, mtypes in conflicts do
                        masks[mclasstype] = compute_mask(mtypes, ids)
                end
                return masks
        end

        private fun compute_mask(mtypes: Set[U], ids: Map[U, Int]): Int do
                var mask = 0
                loop
                        var used = new List[Int]
                        for mtype in mtypes do
                                var res = operator.op(mask, ids[mtype])
                                if used.has(res) then
                                        break
                                else
                                        used.add(res)
                                end
                        end
                        if used.length == mtypes.length then break
                        mask += 1
                end
                return mask
        end

        # Compute hash for each element in each holder
        fun compute_hashes(elements: Map[T, Set[U]], ids: Map[U, Int], masks: Map[T, Int]): Map[T, Map[U, Int]] do
                var hashes = new HashMap[T, Map[U, Int]]
                for mclasstype, mtypes in elements do
                        var mask = masks[mclasstype]
                        var inhashes = new HashMap[U, Int]
                        for mtype in mtypes do
                                inhashes[mtype] = operator.op(mask, ids[mtype])
                        end
                        hashes[mclasstype] = inhashes
                end
                return hashes
        end
end

# Abstract operator used for perfect hashing
abstract class PHOperator
        # hash `id` using `mask`
        fun op(mask: Int, id:Int): Int is abstract
end

# Hashing using modulo (MOD) operator
# slower but compact
class PHModOperator
        super PHOperator
        init do end
        redef fun op(mask, id) do return mask % id
end

# Hashing using binary and (AND) operator
# faster but sparse
class PHAndOperator
        super PHOperator
        init do end
        redef fun op(mask, id) do return mask.bin_and(id)
end

# Layout builder for typing tables using perfect hashing (PH)
class TypingHasher[E: Object]
        super PerfectHasher[E, E]
        super TypingLayoutBuilder[E]

        var mmodule: MModule

        init(operator: PHOperator, mmodule: MModule) do
                super(operator)
                self.mmodule = mmodule
        end

        redef fun build_layout(elements: Set[E]): PHLayout[E, E] do
                var result = new PHLayout[E, E]
                var conflicts = self.build_conflicts(elements)
                result.ids = self.compute_ids(elements)
                result.masks = self.compute_masks(conflicts, result.ids)
                result.hashes = self.compute_hashes(conflicts, result.ids, result.masks)
                return result
        end

        # Ids start from 1 instead of 0
        private fun compute_ids(elements: Set[E]): Map[E, Int] do
                var ids = new HashMap[E, Int]
                var lin = self.reverse_linearize(elements)
                for e in lin do
                        ids[e] = ids.length + 1
                end
                return ids
        end

        private fun build_conflicts(elements: Set[E]): Map[E, Set[E]] do
                var conflicts = new HashMap[E, Set[E]]
                for e in elements do
                        var supers = self.super_elements(e, elements)
                        supers.add(e)
                        conflicts[e] = supers
                end
                return conflicts
        end

        private fun super_elements(element: E, elements: Set[E]): Set[E] is abstract
        private fun reverse_linearize(elements: Set[E]): Array[E] is abstract
end

# Layout builder for typing tables with types using perfect hashing (PH)
class MTypeHasher
        super TypingHasher[MType]

        init(operator: PHOperator, mmodule: MModule) do super(operator, mmodule)

        redef fun super_elements(element, elements) do
                return self.mmodule.super_mtypes(element, elements)
        end

        redef fun reverse_linearize(elements) do
                return self.mmodule.reverse_linearize_mtypes(elements)
        end
end

# Layout builder for typing tables with classes using perfect hashing (PH)
class MClassHasher
        super TypingHasher[MClass]

        init(operator: PHOperator, mmodule: MModule) do super(operator, mmodule)

        redef fun super_elements(element, elements) do
                return self.mmodule.super_mclasses(element)
        end

        redef fun reverse_linearize(elements) do
                return self.mmodule.reverse_linearize_mclasses(elements)
        end
end

# Abstract layout builder for properties tables using perfect hashing (PH)
class MPropertyHasher[E: MProperty]
        super PerfectHasher[MClass, E]
        super PropertyLayoutBuilder[E]

        type MPROP: MProperty

        var mmodule: MModule

        init(operator: PHOperator, mmodule: MModule) do
                super(operator)
                self.mmodule = mmodule
        end

        redef fun build_layout(mclasses) do
                var result = new PHLayout[MClass, E]
                var ids = new HashMap[E, Int]
                var elements = new HashMap[MClass, Set[E]]
                var lin = linearize_mclasses(mclasses)
                for mclass in lin do
                        var mproperties = properties(mclass)
                        for mproperty in mproperties do
                                if ids.has_key(mproperty) then continue
                                ids[mproperty] = ids.length + 1
                        end
                        elements[mclass] = mproperties
                end
                result.ids = ids
                result.pos = ids
                result.masks = self.compute_masks(elements, ids)
                result.hashes = self.compute_hashes(elements, ids, result.masks)
                return result
        end

        # extract set of properties from mclass
        private fun properties(mclass: MClass): Set[E] do
                var properties = new HashSet[E]
                for mprop in self.mmodule.properties(mclass) do
                        if mprop isa MPROP then properties.add(mprop)
                end
                return properties
        end

        private fun linearize_mclasses(mclasses: Set[MClass]): Array[MClass] is abstract
end

# Layout builder for vft using perfect hashing (PH)
class MMethodHasher
        super MPropertyHasher[MMethod]

        redef type MPROP: MMethod
        init(operator: PHOperator, mmodule: MModule) do super(operator, mmodule)
        redef fun linearize_mclasses(mclasses) do return self.mmodule.reverse_linearize_mclasses(mclasses)
end

# Layout builder for attributes tables using perfect hashing (PH)
class MAttributeHasher
        super MPropertyHasher[MAttribute]

        redef type MPROP: MAttribute
        init(operator: PHOperator, mmodule: MModule) do super(operator, mmodule)
        redef fun linearize_mclasses(mclasses) do return self.mmodule.linearize_mclasses_2(mclasses)
end

# Layout builder for virtual types tables using perfect hashing (PH)
class MVirtualTypePropHasher
        super MPropertyHasher[MVirtualTypeProp]

        redef type MPROP: MVirtualTypeProp
        init(operator: PHOperator, mmodule: MModule) do super(operator, mmodule)
        redef fun linearize_mclasses(mclasses) do return self.mmodule.reverse_linearize_mclasses(mclasses)
end

# Layout builder for resolution tables using perfect hashing (PH)
class ResolutionHasher
        super PerfectHasher[MClassType, MType]
        super ResolutionLayoutBuilder

        init(operator: PHOperator) do super(operator)

        # Compute resolved types masks and hashes
        redef fun build_layout(elements) do
                var result = new PHLayout[MClassType, MType]
                var ids = new HashMap[MType, Int]
                var color = 1
                for mclasstype, mclasstypes in elements do
                        for element in mclasstypes do
                                if ids.has_key(element) then continue
                                ids[element] = color
                                color += 1
                        end
                end
                result.ids = ids
                result.pos = ids
                result.masks = self.compute_masks(elements, ids)
                result.hashes = self.compute_hashes(elements, ids, result.masks)
                return result
        end
end