Merge pull request #2392 from chriseth/trieCommon

Some comments for TrieCommon.h

libdevcore/TrieCommon.h

@@ -32,26 +32,38 @@ inline byte nibble(bytesConstRef _data, unsigned _i)
 	return (_i & 1) ? (_data[_i / 2] & 15) : (_data[_i / 2] >> 4);
 }
 
-inline unsigned sharedNibbles(bytesConstRef _a, unsigned _ab, unsigned _ae, bytesConstRef _b, unsigned _bb, unsigned _be)
+/// Interprets @a _first and @a _second as vectors of nibbles and returns the length of the longest common
+/// prefix of _first[_beginFirst..._endFirst] and _second[_beginSecond..._endSecond].
+inline unsigned sharedNibbles(bytesConstRef _first, unsigned _beginFirst, unsigned _endFirst, bytesConstRef _second, unsigned _beginSecond, unsigned _endSecond)
 {
 	unsigned ret = 0;
-	for (unsigned ai = _ab, bi = _bb; ai < _ae && bi < _be && nibble(_a, ai) == nibble(_b, bi); ++ai, ++bi, ++ret) {}
+	while (_beginFirst < _endFirst && _beginSecond < _endSecond && nibble(_first, _beginFirst) == nibble(_second, _beginSecond))
+	{
+		++_beginFirst;
+		++_beginSecond;
+		++ret;
+	}
 	return ret;
 }
 
+/**
+ * Nibble-based view on a bytesConstRef.
+ */
 struct NibbleSlice
 {
 	bytesConstRef data;
 	unsigned offset;
 
-	NibbleSlice(bytesConstRef _d = bytesConstRef(), unsigned _o = 0): data(_d), offset(_o) {}
+	NibbleSlice(bytesConstRef _data = bytesConstRef(), unsigned _offset = 0): data(_data), offset(_offset) {}
 	byte operator[](unsigned _index) const { return nibble(data, offset + _index); }
 	unsigned size() const { return data.size() * 2 - offset; }
 	bool empty() const { return !size(); }
 	NibbleSlice mid(unsigned _index) const { return NibbleSlice(data, offset + _index); }
 	void clear() { data.reset(); offset = 0; }
 
+	/// @returns true iff _k is a prefix of this.
 	bool contains(NibbleSlice _k) const { return shared(_k) == _k.size(); }
+	/// @returns the number of shared nibbles at the beginning of this and _k.
 	unsigned shared(NibbleSlice _k) const { return sharedNibbles(data, offset, offset + size(), _k.data, _k.offset, _k.offset + _k.size()); }
 	/**
 	 * @brief Determine if we, a full key, are situated prior to a particular key-prefix.
@@ -60,8 +72,8 @@ struct NibbleSlice
 	 */
 	bool isEarlierThan(NibbleSlice _k) const
 	{
-		unsigned i;
-		for (i = 0; i < _k.size() && i < size(); ++i)
+		unsigned i = 0;
+		for (; i < _k.size() && i < size(); ++i)
 			if (operator[](i) < _k[i])		// Byte is lower - we're earlier..
 				return true;
 			else if (operator[](i) > _k[i])	// Byte is higher - we're not earlier.