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Dart - make vTable fixed size (expect the number of fields when creating) (#6735)

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This commit is contained in:
Ivan Dlugos
2021-07-19 20:27:01 +02:00
committed by GitHub
parent dd5bb55cad
commit 65700441d3
14 changed files with 103 additions and 87 deletions
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48
dart/lib/flat_buffers.dart
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@@ -472,12 +472,12 @@ class Builder {
}
}
/// Start a new table. Must be finished with [endTable] invocation.
void startTable() {
/// Start a new table. Must be finished with [endTable] invocation.
void startTable(int numFields) {
if (_currentVTable != null) {
throw new StateError('Inline tables are not supported.');
}
_currentVTable = new _VTable();
_currentVTable = new _VTable(numFields);
_currentTableEndTail = _tail;
}
@@ -1229,8 +1229,14 @@ class _FbBoolList extends _FbList<bool> {
class _VTable {
static const int _metadataLength = 4;
final fieldTails = <int?>[];
final fieldOffsets = <int>[];
final int numFields;
// Note: fieldOffsets start as "tail offsets" and are then transformed by
// [computeFieldOffsets()] to actual offsets when a table is finished.
final Uint32List fieldOffsets;
bool offsetsComputed = false;
_VTable(this.numFields) : fieldOffsets = Uint32List(numFields);
/// The size of the table that uses this VTable.
int tableSize = 0;
@@ -1241,17 +1247,20 @@ class _VTable {
int get _vTableSize => numOfUint16 * _sizeofUint16;
int get numOfUint16 => 1 + 1 + fieldTails.length;
int get numOfUint16 => 1 + 1 + numFields;
@pragma('vm:prefer-inline')
void addField(int field, int offset) {
while (fieldTails.length <= field) {
fieldTails.add(null);
}
fieldTails[field] = offset;
assert(!offsetsComputed);
assert(offset > 0); // it's impossible for field to start at the buffer end
assert(offset <= 4294967295); // uint32 max
fieldOffsets[field] = offset;
}
@pragma('vm:prefer-inline')
bool _offsetsMatch(int vt2Start, ByteData buf) {
for (int i = 0; i < fieldOffsets.length; i++) {
assert(offsetsComputed);
for (int i = 0; i < numFields; i++) {
if (fieldOffsets[i] !=
buf.getUint16(vt2Start + _metadataLength + (2 * i), Endian.little)) {
return false;
@@ -1261,17 +1270,22 @@ class _VTable {
}
/// Fill the [fieldOffsets] field.
@pragma('vm:prefer-inline')
void computeFieldOffsets(int tableTail) {
assert(fieldOffsets.isEmpty);
for (int? fieldTail in fieldTails) {
int fieldOffset = fieldTail == null ? 0 : tableTail - fieldTail;
fieldOffsets.add(fieldOffset);
assert(!offsetsComputed);
offsetsComputed = true;
for (var i = 0; i < numFields; i++) {
if (fieldOffsets[i] != 0) {
fieldOffsets[i] = tableTail - fieldOffsets[i];
}
}
}
/// Outputs this VTable to [buf], which is is expected to be aligned to 16-bit
/// and have at least [numOfUint16] 16-bit words available.
@pragma('vm:prefer-inline')
void output(ByteData buf, int bufOffset) {
assert(offsetsComputed);
// VTable size.
buf.setUint16(bufOffset, numOfUint16 * 2, Endian.little);
bufOffset += 2;
@@ -1279,8 +1293,8 @@ class _VTable {
buf.setUint16(bufOffset, tableSize, Endian.little);
bufOffset += 2;
// Field offsets.
for (int fieldOffset in fieldOffsets) {
buf.setUint16(bufOffset, fieldOffset, Endian.little);
for (int i = 0; i < numFields; i++) {
buf.setUint16(bufOffset, fieldOffsets[i], Endian.little);
bufOffset += 2;
}
}