NOT FOR COMMIT: Copying the path command data directly into the path byte stream buffer

third_party/WebKit/Source/core/svg/SVGPathByteStreamBuilder.cpp

Index: third_party/WebKit/Source/core/svg/SVGPathByteStreamBuilder.cpp
diff --git a/third_party/WebKit/Source/core/svg/SVGPathByteStreamBuilder.cpp b/third_party/WebKit/Source/core/svg/SVGPathByteStreamBuilder.cpp
index 86b63718bb82623379f1cc66414b51d059e7459b..74f54f70ef79f35306987d48384359f1fdd7bcc0 100644
--- a/third_party/WebKit/Source/core/svg/SVGPathByteStreamBuilder.cpp
+++ b/third_party/WebKit/Source/core/svg/SVGPathByteStreamBuilder.cpp
@@ -26,19 +26,18 @@
 
 namespace blink {
 
-// Helper class that coalesces writes to a SVGPathByteStream to a local buffer.
-class CoalescingBuffer {
+namespace {
+
+class StreamBufferHelper {
 public:
-    CoalescingBuffer(SVGPathByteStream& byteStream)
-        : m_currentOffset(0)
-        , m_byteStream(byteStream)
-    {
-    }
-    ~CoalescingBuffer()
+    StreamBufferHelper(SVGPathByteStream& byteStream, size_t bytesToReserve)
+        : m_buffer(byteStream.appendUninitialized(bytesToReserve))
     {
-        for (size_t i = 0; i < m_currentOffset; ++i)
-            m_byteStream.append(m_bytes[i]);
+#if ENABLE(ASSERT)
+        m_expectedEnd = m_buffer + bytesToReserve;
+#endif
     }
+    ~StreamBufferHelper() { ASSERT(m_expectedEnd == m_buffer); }
 
     template<typename DataType>
     void writeType(DataType value)
@@ -47,8 +46,8 @@ public:
         data.value = value;
         size_t typeSize = sizeof(ByteType<DataType>);
         ASSERT(m_currentOffset + typeSize <= sizeof(m_bytes));
-        memcpy(m_bytes + m_currentOffset, data.bytes, typeSize);
-        m_currentOffset += typeSize;
+        memcpy(m_buffer, data.bytes, typeSize);
+        m_buffer += typeSize;
     }
 
     void writeFlag(bool value) { writeType<bool>(value); }
@@ -61,21 +60,47 @@ public:
     void writeSegmentType(unsigned short value) { writeType<unsigned short>(value); }
 
 private:
-    // Adjust size to fit the largest command (in serialized/byte-stream format).
-    // Currently a cubic segment.
-    size_t m_currentOffset;
-    unsigned char m_bytes[sizeof(unsigned short) + sizeof(FloatPoint) * 3];
-    SVGPathByteStream& m_byteStream;
+    unsigned char* m_buffer;
+#if ENABLE(ASSERT)
+    const unsigned char* m_expectedEnd;
+#endif
 };
 
+}
+
 SVGPathByteStreamBuilder::SVGPathByteStreamBuilder(SVGPathByteStream& byteStream)
     : m_byteStream(byteStream)
 {
 }
 
+static const unsigned char commandParamLength[] = {
+    0,
+    /* PathSegClosePath */                 0,
+    /* PathSegMoveToAbs */                 sizeof(FloatPoint),
+    /* PathSegMoveToRel */                 sizeof(FloatPoint),
+    /* PathSegLineToAbs */                 sizeof(FloatPoint),
+    /* PathSegLineToRel */                 sizeof(FloatPoint),
+    /* PathSegCurveToCubicAbs */           3 * sizeof(FloatPoint),
+    /* PathSegCurveToCubicRel */           3 * sizeof(FloatPoint),
+    /* PathSegCurveToQuadraticAbs */       2 * sizeof(FloatPoint),
+    /* PathSegCurveToQuadraticRel */       2 * sizeof(FloatPoint),
+    /* PathSegArcAbs */                    2 * sizeof(FloatPoint) + 1 * sizeof(float) + 2 * sizeof(bool),
+    /* PathSegArcRel */                    2 * sizeof(FloatPoint) + 1 * sizeof(float) + 2 * sizeof(bool),
+    /* PathSegLineToHorizontalAbs */       sizeof(float),
+    /* PathSegLineToHorizontalRel */       sizeof(float),
+    /* PathSegLineToVerticalAbs */         sizeof(float),
+    /* PathSegLineToVerticalRel */         sizeof(float),
+    /* PathSegCurveToCubicSmoothAbs */     2 * sizeof(FloatPoint),
+    /* PathSegCurveToCubicSmoothRel */     2 * sizeof(FloatPoint),
+    /* PathSegCurveToQuadraticSmoothAbs */ sizeof(FloatPoint),
+    /* PathSegCurveToQuadraticSmoothRel */ sizeof(FloatPoint)
+};
+
 void SVGPathByteStreamBuilder::emitSegment(const PathSegmentData& segment)
 {
-    CoalescingBuffer buffer(m_byteStream);
+    ASSERT(segment.command > PathSegUnknown && segment.command <= PathSegCurveToQuadraticSmoothRel);
+    size_t commandLength = sizeof(unsigned short) + commandParamLength[segment.command];
+    StreamBufferHelper buffer(m_byteStream, commandLength);
     buffer.writeSegmentType(segment.command);
 
     switch (segment.command) {