Minor MapBuffer renames for consistency

Summary:
Rename `_header` to `header_` to align with the C++ naming scheme we use.
Rename `readKey` to `readUnsignedShort` as purpose of the method have changed.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D33637127

fbshipit-source-id: a82f4d6c1b753b21e0567fbe919af98e4c78105d

Author: Andrei Shikov

ReactAndroid/src/main/java/com/facebook/react/common/mapbuffer/ReadableMapBuffer.java

@@ -92,7 +92,7 @@ private int getBucketIndexForKey(int key) {
     int hi = getCount() - 1;
     while (lo <= hi) {
       final int mid = (lo + hi) >>> 1;
-      final int midVal = readKey(getKeyOffsetForBucketIndex(mid));
+      final int midVal = readUnsignedShort(getKeyOffsetForBucketIndex(mid));
       if (midVal < key) {
         lo = mid + 1;
       } else if (midVal > key) {
@@ -104,7 +104,7 @@ private int getBucketIndexForKey(int key) {
     return -1;
   }
 
-  private int readKey(int position) {
+  private int readUnsignedShort(int position) {
     return mBuffer.getShort(position) & 0xFFFF;
   }
 
@@ -155,7 +155,7 @@ private void readHeader() {
       mBuffer.order(ByteOrder.LITTLE_ENDIAN);
     }
     // count
-    mCount = mBuffer.getShort() & 0xFFFF;
+    mCount = readUnsignedShort(mBuffer.position());
   }
 
   /**
@@ -229,7 +229,7 @@ private ByteBuffer importByteBufferAndReadHeader() {
   }
 
   private void assertKeyExists(int key, int bucketIndex) {
-    int storedKey = readKey(getKeyOffsetForBucketIndex(bucketIndex));
+    int storedKey = readUnsignedShort(getKeyOffsetForBucketIndex(bucketIndex));
     if (storedKey != key) {
       throw new IllegalStateException(
           "Stored key doesn't match parameter - expected: " + key + " - found: " + storedKey);
@@ -289,7 +289,7 @@ private MapBufferEntry(int position) {
 
     /** @return a {@link short} that represents the key of this {@link MapBufferEntry}. */
     public int getKey() {
-      return readKey(mBucketOffset);
+      return readUnsignedShort(mBucketOffset);
     }
 
     /** @return the double value that is stored in this {@link MapBufferEntry}. */

ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.cpp

@@ -40,7 +40,7 @@ void MapBufferBuilder::storeKeyValue(
 
   buckets_.emplace_back(key, data);
 
-  _header.count++;
+  header_.count++;
 
   minKeyToStore_ = key + 1;
 }
@@ -99,10 +99,10 @@ MapBuffer MapBufferBuilder::build() {
   auto bucketSize = buckets_.size() * BUCKET_SIZE;
   uint32_t bufferSize = HEADER_SIZE + bucketSize + dynamicData_.size();
 
-  _header.bufferSize = bufferSize;
+  header_.bufferSize = bufferSize;
 
   std::vector<uint8_t> buffer(bufferSize);
-  memcpy(buffer.data(), &_header, HEADER_SIZE);
+  memcpy(buffer.data(), &header_, HEADER_SIZE);
   memcpy(buffer.data() + HEADER_SIZE, buckets_.data(), bucketSize);
   memcpy(
       buffer.data() + HEADER_SIZE + bucketSize,

ReactCommon/react/renderer/mapbuffer/MapBufferBuilder.h

@@ -23,7 +23,7 @@ constexpr uint16_t INITIAL_BUCKETS_SIZE = 10;
  */
 class MapBufferBuilder {
  private:
-  Header _header = {ALIGNMENT, 0, 0};
+  Header header_ = {ALIGNMENT, 0, 0};
 
   void storeKeyValue(Key key, uint8_t const *value, uint32_t valueSize);