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| 1 # Copyright 2013 The Chromium Authors. All rights reserved. | |
| 2 # Use of this source code is governed by a BSD-style license that can be | |
| 3 # found in the LICENSE file. | |
| 4 | |
| 5 import mojom | |
| 6 | |
| 7 # mojom_pack provides a mechanism for determining the packed order and offsets | |
| 8 # of a mojom.Struct. | |
| 9 # | |
| 10 # ps = mojom_pack.PackedStruct(struct) | |
| 11 # ps.packed_fields will access a list of PackedField objects, each of which | |
| 12 # will have an offset, a size and a bit (for mojom.BOOLs). | |
| 13 | |
| 14 class PackedField(object): | |
| 15 kind_to_size = { | |
| 16 mojom.BOOL: 1, | |
| 17 mojom.INT8: 1, | |
| 18 mojom.UINT8: 1, | |
| 19 mojom.INT16: 2, | |
| 20 mojom.UINT16: 2, | |
| 21 mojom.INT32: 4, | |
| 22 mojom.UINT32: 4, | |
| 23 mojom.FLOAT: 4, | |
| 24 mojom.HANDLE: 4, | |
| 25 mojom.MSGPIPE: 4, | |
| 26 mojom.SHAREDBUFFER: 4, | |
| 27 mojom.DCPIPE: 4, | |
| 28 mojom.DPPIPE: 4, | |
| 29 mojom.INT64: 8, | |
| 30 mojom.UINT64: 8, | |
| 31 mojom.DOUBLE: 8, | |
| 32 mojom.STRING: 8 | |
| 33 } | |
| 34 | |
| 35 @classmethod | |
| 36 def GetSizeForKind(cls, kind): | |
| 37 if isinstance(kind, mojom.Array) or isinstance(kind, mojom.Struct): | |
| 38 return 8 | |
| 39 if isinstance(kind, mojom.Interface): | |
| 40 kind = mojom.MSGPIPE | |
| 41 if isinstance(kind, mojom.Enum): | |
| 42 # TODO(mpcomplete): what about big enums? | |
| 43 return cls.kind_to_size[mojom.INT32] | |
| 44 if not kind in cls.kind_to_size: | |
| 45 raise Exception("Invalid kind: %s" % kind.spec) | |
| 46 return cls.kind_to_size[kind] | |
| 47 | |
| 48 def __init__(self, field, ordinal): | |
| 49 self.field = field | |
| 50 self.ordinal = ordinal | |
| 51 self.size = self.GetSizeForKind(field.kind) | |
| 52 self.offset = None | |
| 53 self.bit = None | |
| 54 | |
| 55 | |
| 56 # Returns the pad necessary to reserve space for alignment of |size|. | |
| 57 def GetPad(offset, size): | |
| 58 return (size - (offset % size)) % size | |
| 59 | |
| 60 | |
| 61 # Returns a 2-tuple of the field offset and bit (for BOOLs) | |
| 62 def GetFieldOffset(field, last_field): | |
| 63 if field.field.kind == mojom.BOOL and \ | |
| 64 last_field.field.kind == mojom.BOOL and \ | |
| 65 last_field.bit < 7: | |
| 66 return (last_field.offset, last_field.bit + 1) | |
| 67 | |
| 68 offset = last_field.offset + last_field.size | |
| 69 pad = GetPad(offset, field.size) | |
| 70 return (offset + pad, 0) | |
| 71 | |
| 72 | |
| 73 class PackedStruct(object): | |
| 74 def __init__(self, struct): | |
| 75 self.struct = struct | |
| 76 self.packed_fields = [] | |
| 77 | |
| 78 # No fields. | |
| 79 if (len(struct.fields) == 0): | |
| 80 return | |
| 81 | |
| 82 # Start by sorting by ordinal. | |
| 83 src_fields = [] | |
| 84 ordinal = 1 | |
| 85 for field in struct.fields: | |
| 86 if field.ordinal is not None: | |
| 87 ordinal = field.ordinal | |
| 88 src_fields.append(PackedField(field, ordinal)) | |
| 89 ordinal += 1 | |
| 90 src_fields.sort(key=lambda field: field.ordinal) | |
| 91 | |
| 92 src_field = src_fields[0] | |
| 93 src_field.offset = 0 | |
| 94 src_field.bit = 0 | |
| 95 # dst_fields will contain each of the fields, in increasing offset order. | |
| 96 dst_fields = self.packed_fields | |
| 97 dst_fields.append(src_field) | |
| 98 | |
| 99 # Then find first slot that each field will fit. | |
| 100 for src_field in src_fields[1:]: | |
| 101 last_field = dst_fields[0] | |
| 102 for i in xrange(1, len(dst_fields)): | |
| 103 next_field = dst_fields[i] | |
| 104 offset, bit = GetFieldOffset(src_field, last_field) | |
| 105 if offset + src_field.size <= next_field.offset: | |
| 106 # Found hole. | |
| 107 src_field.offset = offset | |
| 108 src_field.bit = bit | |
| 109 dst_fields.insert(i, src_field) | |
| 110 break | |
| 111 last_field = next_field | |
| 112 if src_field.offset is None: | |
| 113 # Add to end | |
| 114 src_field.offset, src_field.bit = GetFieldOffset(src_field, last_field) | |
| 115 dst_fields.append(src_field) | |
| 116 | |
| 117 def GetTotalSize(self): | |
| 118 if not self.packed_fields: | |
| 119 return 0; | |
| 120 last_field = self.packed_fields[-1] | |
| 121 offset = last_field.offset + last_field.size | |
| 122 pad = GetPad(offset, 8) | |
| 123 return offset + pad; | |
| 124 | |
| 125 | |
| 126 class ByteInfo(object): | |
| 127 def __init__(self): | |
| 128 self.is_padding = False | |
| 129 self.packed_fields = [] | |
| 130 | |
| 131 | |
| 132 def GetByteLayout(packed_struct): | |
| 133 bytes = [ByteInfo() for i in xrange(packed_struct.GetTotalSize())] | |
| 134 | |
| 135 limit_of_previous_field = 0 | |
| 136 for packed_field in packed_struct.packed_fields: | |
| 137 for i in xrange(limit_of_previous_field, packed_field.offset): | |
| 138 bytes[i].is_padding = True | |
| 139 bytes[packed_field.offset].packed_fields.append(packed_field) | |
| 140 limit_of_previous_field = packed_field.offset + packed_field.size | |
| 141 | |
| 142 for i in xrange(limit_of_previous_field, len(bytes)): | |
| 143 bytes[i].is_padding = True | |
| 144 | |
| 145 for byte in bytes: | |
| 146 # A given byte cannot both be padding and have a fields packed into it. | |
| 147 assert not (byte.is_padding and byte.packed_fields) | |
| 148 | |
| 149 return bytes | |
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