Write and read support for Float64 lists in FlatBuffers.

pkg/analyzer/lib/src/summary/flat_buffers.dart

Index: pkg/analyzer/lib/src/summary/flat_buffers.dart
diff --git a/pkg/analyzer/lib/src/summary/flat_buffers.dart b/pkg/analyzer/lib/src/summary/flat_buffers.dart
index 3c7de13ec9a713ccc5619705dfe72cb07b645810..6aa34a3aff5e9aab1a8a76f12b747f902eca3908 100644
--- a/pkg/analyzer/lib/src/summary/flat_buffers.dart
+++ b/pkg/analyzer/lib/src/summary/flat_buffers.dart
@@ -49,6 +49,9 @@ class BufferPointer {
     return new BufferPointer._(_buffer, _offset + delta);
   }
 
+  double _getFloat64([int delta = 0]) =>
+      _buffer.getFloat64(_offset + delta, Endianness.LITTLE_ENDIAN);
+
   int _getInt32([int delta = 0]) =>
       _buffer.getInt32(_offset + delta, Endianness.LITTLE_ENDIAN);
 
@@ -60,6 +63,9 @@ class BufferPointer {
   int _getUint32([int delta = 0]) =>
       _buffer.getUint32(_offset + delta, Endianness.LITTLE_ENDIAN);
 
+  int _getUint64([int delta = 0]) =>
+      _buffer.getUint64(_offset + delta, Endianness.LITTLE_ENDIAN);
+
   /**
    * If the [byteList] is already a [Uint8List] return it.
    * Otherwise return a [Uint8List] copy of the [byteList].
@@ -299,6 +305,26 @@ class Builder {
   }
 
   /**
+   * Write the given list of 64-bit float [values].
+   */
+  Offset writeListFloat64(List<double> values) {
+    if (_currentVTable != null) {
+      throw new StateError(
+          'Cannot write a non-scalar value while writing a table.');
+    }
+    _prepare(8, 1 + values.length);
+    Offset result = new Offset(_tail);
+    int tail = _tail;
+    _setUint64AtTail(_buf, tail, values.length);
+    tail -= 8;
+    for (double value in values) {
+      _setFloat64AtTail(_buf, tail, value);
+      tail -= 8;
+    }
+    return result;
+  }
+
+  /**
    * Write the given list of signed 32-bit integer [values].
    */
   Offset writeListInt32(List<int> values) {
@@ -383,6 +409,10 @@ class Builder {
     _currentVTable.addField(field, _tail);
   }
 
+  static void _setFloat64AtTail(ByteData _buf, int tail, double x) {
+    _buf.setFloat64(_buf.lengthInBytes - tail, x, Endianness.LITTLE_ENDIAN);
+  }
+
   static void _setInt32AtTail(ByteData _buf, int tail, int x) {
     _buf.setInt32(_buf.lengthInBytes - tail, x, Endianness.LITTLE_ENDIAN);
   }
@@ -390,6 +420,25 @@ class Builder {
   static void _setUint32AtTail(ByteData _buf, int tail, int x) {
     _buf.setUint32(_buf.lengthInBytes - tail, x, Endianness.LITTLE_ENDIAN);
   }
+
+  static void _setUint64AtTail(ByteData _buf, int tail, int x) {
+    _buf.setUint64(_buf.lengthInBytes - tail, x, Endianness.LITTLE_ENDIAN);
+  }
+}
+
+/**
+ * The reader of lists of 64-bit float values.
+ *
+ * The returned unmodifiable lists lazily read values on access.
+ */
+class Float64ListReader extends Reader<List<double>> {
+  const Float64ListReader();
+
+  @override
+  int get size => 4;
+
+  @override
+  List<double> read(BufferPointer bp) => new _FbFloat64List(bp.derefObject());
 }
 
 /**
@@ -433,7 +482,7 @@ class ListReader<E> extends Reader<List<E>> {
 
   @override
   List<E> read(BufferPointer bp) =>
-      new _FbList<E>(_elementReader, bp.derefObject());
+      new _FbInt32List<E>(_elementReader, bp.derefObject());
 }
 
 /**
@@ -519,14 +568,47 @@ abstract class TableReader<T> extends Reader<T> {
   }
 }
 
-class _FbList<E> extends Object with ListMixin<E> implements List<E> {
+/**
+ * The list backed by 64-bit values - Uint64 length and Float64.
+ */
+class _FbFloat64List extends _FbList<double> {
+  final BufferPointer bp;
+
+  int _length;
+  List<double> _items;
+
+  _FbFloat64List(this.bp);
+
+  @override
+  int get length {
+    _length ??= bp._getUint64();
+    return _length;
+  }
+
+  @override
+  double operator [](int i) {
+    _items ??= new List<double>(length);
+    double item = _items[i];
+    if (item == null) {
+      BufferPointer ref = bp._advance(8 + 8 * i);
+      item = ref._getFloat64();
+      _items[i] = item;
+    }
+    return item;
+  }
+}
+
+/**
+ * The list backed by 32-bit values - offsets or integers.
+ */
+class _FbInt32List<E> extends _FbList<E> {
   final Reader<E> elementReader;
   final BufferPointer bp;
 
   int _length;
   List<E> _items;
 
-  _FbList(this.elementReader, this.bp);
+  _FbInt32List(this.elementReader, this.bp);
 
   @override
   int get length {
@@ -535,20 +617,25 @@ class _FbList<E> extends Object with ListMixin<E> implements List<E> {
   }
 
   @override
-  void set length(int i) =>
-      throw new StateError('Attempt to modify immutable list');
-
-  @override
   E operator [](int i) {
     _items ??= new List<E>(length);
     E item = _items[i];
     if (item == null) {
-      BufferPointer ref = bp._advance(4 + elementReader.size * i);
+      BufferPointer ref = bp._advance(4 + 4 * i);
       item = elementReader.read(ref);
       _items[i] = item;
     }
     return item;
   }
+}
+
+/**
+ * An immutable list abstract list.

[Paul Berry, 2016/01/15 22:26:37]

This comment is hard to interpret.  How about something like "base class for
immutable lists read from flatbuffers"?

+ */
+abstract class _FbList<E> extends Object with ListMixin<E> implements List<E> {
+  @override
+  void set length(int i) =>
+      throw new StateError('Attempt to modify immutable list');
 
   @override
   void operator []=(int i, E e) =>