1 # This file is part of NIT ( http://www.nitlanguage.org ).
3 # Copyright 2014 Julien Pagès <julien.pages@lirmm.fr>
5 # Licensed under the Apache License, Version 2.0 (the "License");
6 # you may not use this file except in compliance with the License.
7 # You may obtain a copy of the License at
9 # http://www.apache.org/licenses/LICENSE-2.0
11 # Unless required by applicable law or agreed to in writing, software
12 # distributed under the License is distributed on an "AS IS" BASIS,
13 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 # See the License for the specific language governing permissions and
15 # limitations under the License.
17 # Implementation of the Nit virtual machine
20 import interpreter
::naive_interpreter
22 import perfect_hashing
24 redef class ModelBuilder
25 redef fun run_naive_interpreter
(mainmodule
: MModule, arguments
: Array[String])
28 self.toolcontext
.info
("*** NITVM STARTING ***", 1)
30 var interpreter
= new VirtualMachine(self, mainmodule
, arguments
)
31 interpreter
.start
(mainmodule
)
34 self.toolcontext
.info
("*** NITVM STOPPING : {time1-time0} ***", 2)
38 # A virtual machine based on the naive_interpreter
39 class VirtualMachine super NaiveInterpreter
41 # Perfect hashing and perfect numbering
42 var ph
: Perfecthashing = new Perfecthashing
44 # Handles memory allocated in C
45 var memory_manager
: MemoryManager = new MemoryManager
47 # The unique instance of the `MInit` value
48 var initialization_value
: Instance
50 init(modelbuilder
: ModelBuilder, mainmodule
: MModule, arguments
: Array[String])
52 var init_type
= new MInitType(mainmodule
.model
)
53 initialization_value
= new MutableInstance(init_type
)
57 # Subtyping test for the virtual machine
58 redef fun is_subtype
(sub
, sup
: MType): Bool
60 var anchor
= self.frame
.arguments
.first
.mtype
.as(MClassType)
61 var sup_accept_null
= false
62 if sup
isa MNullableType then
63 sup_accept_null
= true
65 else if sup
isa MNullType then
66 sup_accept_null
= true
69 # Can `sub` provides null or not?
70 # Thus we can match with `sup_accept_null`
71 # Also discard the nullable marker if it exists
72 if sub
isa MNullableType then
73 if not sup_accept_null
then return false
75 else if sub
isa MNullType then
76 return sup_accept_null
78 # Now the case of direct null and nullable is over
80 # An unfixed formal type can only accept itself
81 if sup
isa MParameterType or sup
isa MVirtualType then
85 if sub
isa MParameterType or sub
isa MVirtualType then
86 sub
= sub
.anchor_to
(mainmodule
, anchor
)
87 # Manage the second layer of null/nullable
88 if sub
isa MNullableType then
89 if not sup_accept_null
then return false
91 else if sub
isa MNullType then
92 return sup_accept_null
96 assert sub
isa MClassType
98 # `sup` accepts only null
99 if sup
isa MNullType then return false
101 assert sup
isa MClassType
103 # Create the sup vtable if not create
104 if not sup
.mclass
.loaded
then create_class
(sup
.mclass
)
106 # Sub can be discovered inside a Generic type during the subtyping test
107 if not sub
.mclass
.loaded
then create_class
(sub
.mclass
)
109 if sup
isa MGenericType then
110 var sub2
= sub
.supertype_to
(mainmodule
, anchor
, sup
.mclass
)
111 assert sub2
.mclass
== sup
.mclass
113 for i
in [0..sup
.mclass
.arity
[ do
114 var sub_arg
= sub2
.arguments
[i
]
115 var sup_arg
= sup
.arguments
[i
]
116 var res
= is_subtype
(sub_arg
, sup_arg
)
118 if res
== false then return false
123 var super_id
= sup
.mclass
.vtable
.id
124 var mask
= sub
.mclass
.vtable
.mask
126 return inter_is_subtype
(super_id
, mask
, sub
.mclass
.vtable
.internal_vtable
)
129 # Subtyping test with perfect hashing
130 private fun inter_is_subtype
(id
: Int, mask
:Int, vtable
: Pointer): Bool `{
131 // hv is the position in hashtable
134 // Follow the pointer to somewhere in the vtable
135 long unsigned int *offset = (long unsigned int*)(((long int *)vtable)[-hv]);
137 // If the pointed value is corresponding to the identifier, the test is true, otherwise false
138 return *offset == id;
141 # Redef init_instance to simulate the loading of a class
142 redef fun init_instance
(recv
: Instance)
144 if not recv
.mtype
.as(MClassType).mclass
.loaded
then create_class
(recv
.mtype
.as(MClassType).mclass
)
146 recv
.vtable
= recv
.mtype
.as(MClassType).mclass
.vtable
148 assert recv
isa MutableInstance
150 recv
.internal_attributes
= init_internal_attributes
(initialization_value
, recv
.mtype
.as(MClassType).mclass
.all_mattributes
(mainmodule
, none_visibility
).length
)
154 # Associate a `PrimitiveInstance` to its `VTable`
155 redef fun init_instance_primitive
(recv
: Instance)
157 if not recv
.mtype
.as(MClassType).mclass
.loaded
then create_class
(recv
.mtype
.as(MClassType).mclass
)
159 recv
.vtable
= recv
.mtype
.as(MClassType).mclass
.vtable
162 # Create a virtual table for this `MClass` if not already done
163 redef fun get_primitive_class
(name
: String): MClass
167 if not mclass
.loaded
then create_class
(mclass
)
172 # Initialize the internal representation of an object (its attribute values)
173 # `init_instance` is the initial value of attributes
174 private fun init_internal_attributes
(init_instance
: Instance, size
: Int): Pointer
175 import Array[Instance].length
, Array[Instance].[] `{
177 Instance* attributes = malloc(sizeof(Instance) * size);
180 for(i=0; i<size; i++)
181 attributes[i] = init_instance;
183 Instance_incr_ref(init_instance);
187 # Creates the runtime structures for this class
188 fun create_class
(mclass
: MClass) do mclass
.make_vt
(self)
190 # Execute `mproperty` for a `args` (where `args[0]` is the receiver).
191 redef fun send
(mproperty
: MMethod, args
: Array[Instance]): nullable Instance
193 var recv
= args
.first
194 var mtype
= recv
.mtype
195 var ret
= send_commons
(mproperty
, args
, mtype
)
196 if ret
!= null then return ret
198 var propdef
= method_dispatch
(mproperty
, recv
.vtable
.as(not null))
200 return self.call
(propdef
, args
)
203 # Method dispatch, for a given global method `mproperty`
204 # returns the most specific local method in the class corresponding to `vtable`
205 private fun method_dispatch
(mproperty
: MMethod, vtable
: VTable): MMethodDef
207 return method_dispatch_ph
(vtable
.internal_vtable
, vtable
.mask
,
208 mproperty
.intro_mclassdef
.mclass
.vtable
.id
, mproperty
.offset
)
211 # Execute a method dispatch with perfect hashing
212 private fun method_dispatch_ph
(vtable
: Pointer, mask
: Int, id
: Int, offset
: Int): MMethodDef `{
213 // Perfect hashing position
215 long unsigned int *pointer = (long unsigned int*)(((long int *)vtable)[-hv]);
217 // pointer+2 is the position where methods are
218 // Add the offset of property and get the method implementation
219 MMethodDef propdef = (MMethodDef)*(pointer + 2 + offset);
224 # Return the value of the attribute `mproperty` for the object `recv`
225 redef fun read_attribute
(mproperty
: MAttribute, recv
: Instance): Instance
227 assert recv
isa MutableInstance
231 if mproperty
.intro_mclassdef
.mclass
.positions_attributes
[recv
.mtype
.as(MClassType).mclass
] != -1 then
232 # if this attribute class has an unique position for this receiver, then use direct access
233 i
= read_attribute_sst
(recv
.internal_attributes
, mproperty
.absolute_offset
)
235 # Otherwise, read the attribute value with perfect hashing
236 var id
= mproperty
.intro_mclassdef
.mclass
.vtable
.id
238 i
= read_attribute_ph
(recv
.internal_attributes
, recv
.vtable
.internal_vtable
,
239 recv
.vtable
.mask
, id
, mproperty
.offset
)
242 # If we get a `MInit` value, throw an error
243 if i
== initialization_value
then
244 fatal
("Uninitialized attribute {mproperty.name}")
251 # Return the attribute value in `instance` with a sequence of perfect_hashing
252 # * `instance` is the attributes array of the receiver
253 # * `vtable` is the pointer to the virtual table of the class (of the receiver)
254 # * `mask` is the perfect hashing mask of the class
255 # * `id` is the identifier of the class
256 # * `offset` is the relative offset of this attribute
257 private fun read_attribute_ph
(instance
: Pointer, vtable
: Pointer, mask
: Int, id
: Int, offset
: Int): Instance `{
258 // Perfect hashing position
260 long unsigned int *pointer = (long unsigned int*)(((long int *)vtable)[-hv]);
262 // pointer+1 is the position where the delta of the class is
263 int absolute_offset = *(pointer + 1);
265 Instance res = ((Instance *)instance)[absolute_offset + offset];
270 # Return the attribute value in `instance` with a direct access (SST)
271 # * `instance` is the attributes array of the receiver
272 # * `offset` is the absolute offset of this attribute
273 private fun read_attribute_sst
(instance
: Pointer, offset
: Int): Instance `{
274 /* We can make a direct access to the attribute value
275 because this attribute is always at the same position
276 for the class of this receiver */
277 Instance res = ((Instance *)instance)[offset];
282 # Replace in `recv` the value of the attribute `mproperty` by `value`
283 redef fun write_attribute
(mproperty
: MAttribute, recv
: Instance, value
: Instance)
285 assert recv
isa MutableInstance
287 # Replace the old value of mproperty in recv
288 if mproperty
.intro_mclassdef
.mclass
.positions_attributes
[recv
.mtype
.as(MClassType).mclass
] != -1 then
289 # if this attribute class has an unique position for this receiver, then use direct access
290 write_attribute_sst
(recv
.internal_attributes
, mproperty
.absolute_offset
, value
)
292 # Otherwise, use perfect hashing to replace the old value
293 var id
= mproperty
.intro_mclassdef
.mclass
.vtable
.id
295 write_attribute_ph
(recv
.internal_attributes
, recv
.vtable
.internal_vtable
,
296 recv
.vtable
.mask
, id
, mproperty
.offset
, value
)
300 # Replace the value of an attribute in an instance
301 # * `instance` is the attributes array of the receiver
302 # * `vtable` is the pointer to the virtual table of the class (of the receiver)
303 # * `mask` is the perfect hashing mask of the class
304 # * `id` is the identifier of the class
305 # * `offset` is the relative offset of this attribute
306 # * `value` is the new value for this attribute
307 private fun write_attribute_ph
(instance
: Pointer, vtable
: Pointer, mask
: Int, id
: Int, offset
: Int, value
: Instance) `{
308 // Perfect hashing position
310 long unsigned int *pointer = (long unsigned int*)(((long int *)vtable)[-hv]);
312 // pointer+1 is the position where the delta of the class is
313 int absolute_offset = *(pointer + 1);
315 ((Instance *)instance)[absolute_offset + offset] = value;
316 Instance_incr_ref(value);
319 # Replace the value of an attribute in an instance with direct access
320 # * `instance` is the attributes array of the receiver
321 # * `offset` is the absolute offset of this attribute
322 # * `value` is the new value for this attribute
323 private fun write_attribute_sst
(instance
: Pointer, offset
: Int, value
: Instance) `{
324 // Direct access to the position with the absolute offset
325 ((Instance *)instance)[offset] = value;
326 Instance_incr_ref(value);
329 # Is the attribute `mproperty` initialized in the instance `recv`?
330 redef fun isset_attribute
(mproperty
: MAttribute, recv
: Instance): Bool
332 assert recv
isa MutableInstance
334 # Read the attribute value with internal perfect hashing read
335 # because we do not want to throw an error if the value is `initialization_value`
336 var id
= mproperty
.intro_mclassdef
.mclass
.vtable
.id
338 var i
= read_attribute_ph
(recv
.internal_attributes
, recv
.vtable
.internal_vtable
,
339 recv
.vtable
.mask
, id
, mproperty
.offset
)
341 return i
!= initialization_value
346 # A reference to the virtual table of this class
347 var vtable
: nullable VTable
349 # True when the class is effectively loaded by the vm, false otherwise
350 var loaded
: Bool = false
352 # For each loaded subclass, keep the position of the group of attributes
353 # introduced by self class in the object
354 var positions_attributes
: HashMap[MClass, Int] = new HashMap[MClass, Int]
356 # For each loaded subclass, keep the position of the group of methods
357 # introduced by self class in the vtable
358 var positions_methods
: HashMap[MClass, Int] = new HashMap[MClass, Int]
360 # Allocates a VTable for this class and gives it an id
361 private fun make_vt
(v
: VirtualMachine)
363 if loaded
then return
365 # `superclasses` contains the order of superclasses for virtual tables
366 var superclasses
= superclasses_ordering
(v
)
367 superclasses
.remove
(self)
369 # Make_vt for super-classes
370 var ids
= new Array[Int]
371 var nb_methods
= new Array[Int]
372 var nb_attributes
= new Array[Int]
374 # Absolute offset of attribute from the beginning of the attributes table
375 var offset_attributes
= 0
376 # Absolute offset of method from the beginning of the methods table
377 var offset_methods
= 0
379 # The previous element in `superclasses`
380 var previous_parent
: nullable MClass = null
381 if superclasses
.length
> 0 then previous_parent
= superclasses
[0]
382 for parent
in superclasses
do
383 if not parent
.loaded
then parent
.make_vt
(v
)
385 # Get the number of introduced methods and attributes for this class
389 for p
in parent
.intro_mproperties
(none_visibility
) do
390 if p
isa MMethod then methods
+= 1
391 if p
isa MAttribute then attributes
+= 1
394 ids
.push
(parent
.vtable
.id
)
395 nb_methods
.push
(methods
)
396 nb_attributes
.push
(attributes
)
398 # Update `positions_attributes` and `positions_methods` in `parent`.
399 # If the position is invariant for this parent, store this position
400 # else store a special value (-1)
404 if previous_parent
.as(not null).positions_attributes
[parent
] == offset_attributes
then pos_attr
= offset_attributes
405 if previous_parent
.as(not null).positions_methods
[parent
] == offset_methods
then pos_meth
= offset_methods
407 parent
.update_positions
(pos_attr
, pos_meth
, self)
409 offset_attributes
+= attributes
410 offset_methods
+= methods
413 # When all super-classes have their identifiers and vtables, allocate current one
414 allocate_vtable
(v
, ids
, nb_methods
, nb_attributes
, offset_attributes
, offset_methods
)
417 # The virtual table now needs to be filled with pointer to methods
418 superclasses
.add
(self)
419 for cl
in superclasses
do
420 fill_vtable
(v
, vtable
.as(not null), cl
)
424 # Allocate a single vtable
425 # * `ids : Array of superclasses identifiers
426 # * `nb_methods : Array which contain the number of introduced methods for each class in ids
427 # * `nb_attributes : Array which contain the number of introduced attributes for each class in ids
428 # * `offset_attributes : Offset from the beginning of the table of the group of attributes
429 # * `offset_methods : Offset from the beginning of the table of the group of methods
430 private fun allocate_vtable
(v
: VirtualMachine, ids
: Array[Int], nb_methods
: Array[Int], nb_attributes
: Array[Int],
431 offset_attributes
: Int, offset_methods
: Int)
434 var idc
= new Array[Int]
436 vtable
.mask
= v
.ph
.pnand
(ids
, 1, idc
) - 1
438 vtable
.classname
= name
440 # Add current id to Array of super-ids
441 var ids_total
= new Array[Int]
442 ids_total
.add_all
(ids
)
443 ids_total
.push
(vtable
.id
)
445 var nb_methods_total
= new Array[Int]
446 var nb_attributes_total
= new Array[Int]
449 var nb_introduced_attributes
= 0
451 # Fixing offsets for self attributes and methods
452 var relative_offset_attr
= 0
453 var relative_offset_meth
= 0
454 for p
in intro_mproperties
(none_visibility
) do
455 if p
isa MMethod then
457 p
.offset
= relative_offset_meth
458 p
.absolute_offset
= offset_methods
+ relative_offset_meth
459 relative_offset_meth
+= 1
461 if p
isa MAttribute then
462 nb_introduced_attributes
+= 1
463 p
.offset
= relative_offset_attr
464 p
.absolute_offset
= offset_attributes
+ relative_offset_attr
465 relative_offset_attr
+= 1
469 nb_methods_total
.add_all
(nb_methods
)
470 nb_methods_total
.push
(self_methods
)
472 nb_attributes_total
.add_all
(nb_attributes
)
473 nb_attributes_total
.push
(nb_introduced_attributes
)
475 # Save the offsets of self class
476 update_positions
(offset_attributes
, offset_methods
, self)
478 # Since we have the number of attributes for each class, calculate the delta
479 var deltas
= calculate_delta
(nb_attributes_total
)
480 vtable
.internal_vtable
= v
.memory_manager
.init_vtable
(ids_total
, nb_methods_total
, deltas
, vtable
.mask
)
483 # Fill the vtable with methods of `self` class
484 # * `v` : Current instance of the VirtualMachine
485 # * `table` : the table of self class, will be filled with its methods
486 private fun fill_vtable
(v
:VirtualMachine, table
: VTable, cl
: MClass)
488 var methods
= new Array[MMethodDef]
489 for m
in cl
.intro_mproperties
(none_visibility
) do
490 if m
isa MMethod then
491 # `propdef` is the most specific implementation for this MMethod
492 var propdef
= m
.lookup_first_definition
(v
.mainmodule
, self.intro
.bound_mtype
)
493 methods
.push
(propdef
)
497 # Call a method in C to put propdefs of self methods in the vtables
498 v
.memory_manager
.put_methods
(vtable
.internal_vtable
, vtable
.mask
, cl
.vtable
.id
, methods
)
501 # Computes delta for each class
502 # A delta represents the offset for this group of attributes in the object
503 # *`nb_attributes` : number of attributes for each class (classes are linearized from Object to current)
504 # * return deltas for each class
505 private fun calculate_delta
(nb_attributes
: Array[Int]): Array[Int]
507 var deltas
= new Array[Int]
510 for nb
in nb_attributes
do
518 # Order superclasses of self
519 # Return the order of superclasses in runtime structures of this class
520 private fun superclasses_ordering
(v
: VirtualMachine): Array[MClass]
522 var superclasses
= new Array[MClass]
523 superclasses
.add_all
(ancestors
)
525 var res
= new Array[MClass]
526 if superclasses
.length
> 1 then
528 var ordering
= self.dfs
(v
, res
)
532 # There is no super-class, self is Object
537 # A kind of Depth-First-Search for superclasses ordering
538 # *`v` : the current executed instance of VirtualMachine
539 # * `res` : Result Array, ie current superclasses ordering
540 private fun dfs
(v
: VirtualMachine, res
: Array[MClass]): Array[MClass]
542 # Add this class at the beginning
545 var direct_parents
= self.in_hierarchy
(v
.mainmodule
).direct_greaters
.to_a
547 if direct_parents
.length
> 1 then
548 # Prefix represents the class which has the most properties
549 # we try to choose it in first to reduce the number of potential recompilations
552 for cl
in direct_parents
do
553 # If we never have visited this class
554 if not res
.has
(cl
) then
555 var properties_length
= cl
.all_mproperties
(v
.mainmodule
, none_visibility
).length
556 if properties_length
> max
then
557 max
= properties_length
563 if prefix
!= null then
564 # Add the prefix class ordering at the beginning of our sequence
565 var prefix_res
= new Array[MClass]
566 prefix_res
= prefix
.dfs
(v
, prefix_res
)
568 # Then we recurse on other classes
569 for cl
in direct_parents
do
571 res
= new Array[MClass]
575 if not prefix_res
.has
(cl_res
) then prefix_res
.push
(cl_res
)
584 if direct_parents
.length
> 0 then
585 res
= direct_parents
.first
.dfs
(v
, res
)
589 if not res
.has
(self) then res
.push
(self)
594 # Update positions of the class `cl`
595 # * `attributes_offset`: absolute offset of introduced attributes
596 # * `methods_offset`: absolute offset of introduced methods
597 private fun update_positions
(attributes_offsets
: Int, methods_offset
:Int, cl
: MClass)
599 positions_attributes
[cl
] = attributes_offsets
600 positions_methods
[cl
] = methods_offset
604 redef class MAttribute
605 # Relative offset of this attribute in the runtime instance
606 # (beginning of the block of its introducing class)
609 # Absolute offset of this attribute in the runtime instance (beginning of the attribute table)
610 var absolute_offset
: Int
614 # Relative offset of this method in the virtual table (from the beginning of the block)
617 # Absolute offset of this method in the virtual table (from the beginning of the vtable)
618 var absolute_offset
: Int
621 # Redef MutableInstance to improve implementation of attributes in objects
622 redef class MutableInstance
624 # C-array to store pointers to attributes of this Object
625 var internal_attributes
: Pointer
628 # Redef to associate an `Instance` to its `VTable`
630 var vtable
: nullable VTable
633 # Is the type of the initial value inside attributes
637 redef var model
: Model
638 protected init(model
: Model)
643 redef fun to_s
do return "InitType"
644 redef fun as_nullable
do return self
645 redef fun need_anchor
do return false
646 redef fun resolve_for
(mtype
, anchor
, mmodule
, cleanup_virtual
) do return self
647 redef fun can_resolve_for
(mtype
, anchor
, mmodule
) do return true
649 redef fun collect_mclassdefs
(mmodule
) do return new HashSet[MClassDef]
651 redef fun collect_mclasses
(mmodule
) do return new HashSet[MClass]
653 redef fun collect_mtypes
(mmodule
) do return new HashSet[MClassType]
656 # A VTable contains the virtual method table for the dispatch
657 # and informations to perform subtyping tests
659 # The mask to perform perfect hashing
660 var mask
: Int is noinit
662 # Unique identifier given by perfect hashing
663 var id
: Int is noinit
665 # Pointer to the c-allocated area, represents the virtual table
666 var internal_vtable
: Pointer is noinit
668 # The short classname of this class
669 var classname
: String is noinit
672 # Handle memory, used for allocate virtual table and associated structures
675 # Allocate and fill a virtual table
676 fun init_vtable
(ids
: Array[Int], nb_methods
: Array[Int], nb_attributes
: Array[Int], mask
: Int): Pointer
678 # Allocate in C current virtual table
679 var res
= intern_init_vtable
(ids
, nb_methods
, nb_attributes
, mask
)
684 # Construct virtual tables with a bi-dimensional layout
685 private fun intern_init_vtable
(ids
: Array[Int], nb_methods
: Array[Int], deltas
: Array[Int], mask
: Int): Pointer
686 import Array[Int].length
, Array[Int].[] `{
688 // Allocate and fill current virtual table
690 int total_size = 0; // total size of this virtual table
691 int nb_classes = Array_of_Int_length(nb_methods);
692 for(i = 0; i<nb_classes; i++) {
693 /* - One for each method of this class
694 * - One for the delta (offset of this group of attributes in objects)
697 total_size += Array_of_Int__index(nb_methods, i);
701 // Add the size of the perfect hashtable (mask +1)
702 // Add one because we start to fill the vtable at position 1 (0 is the init position)
703 total_size += mask+2;
704 long unsigned int* vtable = malloc(sizeof(long unsigned int)*total_size);
706 // Initialisation to the first position of the virtual table (ie : Object)
707 long unsigned int *init = vtable + mask + 2;
708 for(i=0; i<total_size; i++)
709 vtable[i] = (long unsigned int)init;
711 // Set the virtual table to its position 0
712 // ie: after the hashtable
713 vtable = vtable + mask + 1;
715 int current_size = 1;
716 for(i = 0; i < nb_classes; i++) {
718 vtable[hv] contains a pointer to the group of introduced methods
719 For each superclasse we have in virtual table :
720 (id | delta | introduced methods)
722 int hv = mask & Array_of_Int__index(ids, i);
724 vtable[current_size] = Array_of_Int__index(ids, i);
725 vtable[current_size + 1] = Array_of_Int__index(deltas, i);
726 vtable[-hv] = (long unsigned int)&(vtable[current_size]);
729 current_size += Array_of_Int__index(nb_methods, i);
735 # Put implementation of methods of a class in `vtable`
736 # * `vtable` : Pointer to the C-virtual table
737 # * `mask` : perfect-hashing mask of the class corresponding to the vtable
738 # * `id` : id of the target class
739 # * `methods` : array of MMethodDef of the target class
740 fun put_methods
(vtable
: Pointer, mask
: Int, id
: Int, methods
: Array[MMethodDef])
741 import Array[MMethodDef].length
, Array[MMethodDef].[] `{
743 // Get the area to fill with methods by a sequence of perfect hashing
745 long unsigned int *pointer = (long unsigned int*)(((long unsigned int *)vtable)[-hv]);
747 // pointer+2 is the beginning of the area for methods implementation
748 int length = Array_of_MMethodDef_length(methods);
749 long unsigned int *area = (pointer + 2);
752 for(i=0; i<length; i++)
754 MMethodDef method = Array_of_MMethodDef__index(methods, i);
755 area[i] = (long unsigned int)method;
756 MMethodDef_incr_ref(method);