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# Copyright 2013 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
from mojom.generate import module as mojom
# This module provides a mechanism for determining the packed order and offsets
# of a mojom.Struct.
#
# ps = pack.PackedStruct(struct)
# ps.packed_fields will access a list of PackedField objects, each of which
# will have an offset, a size and a bit (for mojom.BOOLs).
# Size of struct header in bytes: num_bytes [4B] + version [4B].
HEADER_SIZE = 8
class PackedField(object):
kind_to_size = {
mojom.BOOL: 1,
mojom.INT8: 1,
mojom.UINT8: 1,
mojom.INT16: 2,
mojom.UINT16: 2,
mojom.INT32: 4,
mojom.UINT32: 4,
mojom.FLOAT: 4,
mojom.HANDLE: 4,
mojom.MSGPIPE: 4,
mojom.SHAREDBUFFER: 4,
mojom.PLATFORMHANDLE: 4,
mojom.DCPIPE: 4,
mojom.DPPIPE: 4,
mojom.NULLABLE_HANDLE: 4,
mojom.NULLABLE_MSGPIPE: 4,
mojom.NULLABLE_SHAREDBUFFER: 4,
mojom.NULLABLE_PLATFORMHANDLE: 4,
mojom.NULLABLE_DCPIPE: 4,
mojom.NULLABLE_DPPIPE: 4,
mojom.INT64: 8,
mojom.UINT64: 8,
mojom.DOUBLE: 8,
mojom.STRING: 8,
mojom.NULLABLE_STRING: 8
}
@classmethod
def GetSizeForKind(cls, kind):
if isinstance(kind, (mojom.Array, mojom.Map, mojom.Struct, mojom.Interface,
mojom.AssociatedInterface, mojom.PendingRemote,
mojom.PendingAssociatedRemote)):
return 8
if isinstance(kind, mojom.Union):
return 16
if isinstance(kind, (mojom.InterfaceRequest, mojom.PendingReceiver)):
kind = mojom.MSGPIPE
if isinstance(
kind,
(mojom.AssociatedInterfaceRequest, mojom.PendingAssociatedReceiver)):
return 4
if isinstance(kind, mojom.Enum):
# TODO(mpcomplete): what about big enums?
return cls.kind_to_size[mojom.INT32]
if not kind in cls.kind_to_size:
raise Exception("Undefined type: %s. Did you forget to import the file "
"containing the definition?" % kind.spec)
return cls.kind_to_size[kind]
@classmethod
def GetAlignmentForKind(cls, kind):
if isinstance(kind, (mojom.Interface, mojom.AssociatedInterface,
mojom.PendingRemote, mojom.PendingAssociatedRemote)):
return 4
if isinstance(kind, mojom.Union):
return 8
return cls.GetSizeForKind(kind)
def __init__(self, field, index, ordinal):
"""
Args:
field: the original field.
index: the position of the original field in the struct.
ordinal: the ordinal of the field for serialization.
"""
self.field = field
self.index = index
self.ordinal = ordinal
self.size = self.GetSizeForKind(field.kind)
self.alignment = self.GetAlignmentForKind(field.kind)
self.offset = None
self.bit = None
self.min_version = None
def GetPad(offset, alignment):
"""Returns the pad necessary to reserve space so that |offset + pad| equals to
some multiple of |alignment|."""
return (alignment - (offset % alignment)) % alignment
def GetFieldOffset(field, last_field):
"""Returns a 2-tuple of the field offset and bit (for BOOLs)."""
if (field.field.kind == mojom.BOOL and last_field.field.kind == mojom.BOOL
and last_field.bit < 7):
return (last_field.offset, last_field.bit + 1)
offset = last_field.offset + last_field.size
pad = GetPad(offset, field.alignment)
return (offset + pad, 0)
def GetPayloadSizeUpToField(field):
"""Returns the payload size (not including struct header) if |field| is the
last field.
"""
if not field:
return 0
offset = field.offset + field.size
pad = GetPad(offset, 8)
return offset + pad
class PackedStruct(object):
def __init__(self, struct):
self.struct = struct
# |packed_fields| contains all the fields, in increasing offset order.
self.packed_fields = []
# |packed_fields_in_ordinal_order| refers to the same fields as
# |packed_fields|, but in ordinal order.
self.packed_fields_in_ordinal_order = []
# No fields.
if (len(struct.fields) == 0):
return
# Start by sorting by ordinal.
src_fields = self.packed_fields_in_ordinal_order
ordinal = 0
for index, field in enumerate(struct.fields):
if field.ordinal is not None:
ordinal = field.ordinal
src_fields.append(PackedField(field, index, ordinal))
ordinal += 1
src_fields.sort(key=lambda field: field.ordinal)
# Set |min_version| for each field.
next_min_version = 0
for packed_field in src_fields:
if packed_field.field.min_version is None:
assert next_min_version == 0
else:
assert packed_field.field.min_version >= next_min_version
next_min_version = packed_field.field.min_version
packed_field.min_version = next_min_version
if (packed_field.min_version != 0
and mojom.IsReferenceKind(packed_field.field.kind)
and not packed_field.field.kind.is_nullable):
raise Exception("Non-nullable fields are only allowed in version 0 of "
"a struct. %s.%s is defined with [MinVersion=%d]." %
(self.struct.name, packed_field.field.name,
packed_field.min_version))
src_field = src_fields[0]
src_field.offset = 0
src_field.bit = 0
dst_fields = self.packed_fields
dst_fields.append(src_field)
# Then find first slot that each field will fit.
for src_field in src_fields[1:]:
last_field = dst_fields[0]
for i in range(1, len(dst_fields)):
next_field = dst_fields[i]
offset, bit = GetFieldOffset(src_field, last_field)
if offset + src_field.size <= next_field.offset:
# Found hole.
src_field.offset = offset
src_field.bit = bit
dst_fields.insert(i, src_field)
break
last_field = next_field
if src_field.offset is None:
# Add to end
src_field.offset, src_field.bit = GetFieldOffset(src_field, last_field)
dst_fields.append(src_field)
class ByteInfo(object):
def __init__(self):
self.is_padding = False
self.packed_fields = []
def GetByteLayout(packed_struct):
total_payload_size = GetPayloadSizeUpToField(
packed_struct.packed_fields[-1] if packed_struct.packed_fields else None)
byte_info = [ByteInfo() for i in range(total_payload_size)]
limit_of_previous_field = 0
for packed_field in packed_struct.packed_fields:
for i in range(limit_of_previous_field, packed_field.offset):
byte_info[i].is_padding = True
byte_info[packed_field.offset].packed_fields.append(packed_field)
limit_of_previous_field = packed_field.offset + packed_field.size
for i in range(limit_of_previous_field, len(byte_info)):
byte_info[i].is_padding = True
for byte in byte_info:
# A given byte cannot both be padding and have a fields packed into it.
assert not (byte.is_padding and byte.packed_fields)
return byte_info
class VersionInfo(object):
def __init__(self, version, num_fields, num_bytes):
self.version = version
self.num_fields = num_fields
self.num_bytes = num_bytes
def GetVersionInfo(packed_struct):
"""Get version information for a struct.
Args:
packed_struct: A PackedStruct instance.
Returns:
A non-empty list of VersionInfo instances, sorted by version in increasing
order.
Note: The version numbers may not be consecutive.
"""
versions = []
last_version = 0
last_num_fields = 0
last_payload_size = 0
for packed_field in packed_struct.packed_fields_in_ordinal_order:
if packed_field.min_version != last_version:
versions.append(
VersionInfo(last_version, last_num_fields,
last_payload_size + HEADER_SIZE))
last_version = packed_field.min_version
last_num_fields += 1
# The fields are iterated in ordinal order here. However, the size of a
# version is determined by the last field of that version in pack order,
# instead of ordinal order. Therefore, we need to calculate the max value.
last_payload_size = max(
GetPayloadSizeUpToField(packed_field), last_payload_size)
assert len(versions) == 0 or last_num_fields != versions[-1].num_fields
versions.append(
VersionInfo(last_version, last_num_fields,
last_payload_size + HEADER_SIZE))
return versions
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