packet buffer comment fix and support for inserting NULLs

include/libtorrent/packet_buffer.hpp

@@ -45,18 +45,19 @@ namespace libtorrent
 	// old elements are removed when new elements are inserted,
 	// the buffer will be resized.
 
-	// if m_mask is 0xf, m_array has 16 elements
+	// m_capacity is the number of elements in m_array
-	// m_cursor is the lowest index that has an element
+	// and must be an even 2^x.
+	// m_first is the lowest index that has an element
 	// it also determines which indices the other slots
 	// refers to. Since it's a circular buffer, it wraps
 	// around. For example
 
-	//                    m_cursor = 9
+	//                    m_first = 9
 	//                    |           refers to index 14
 	//                    |           |
 	//                    V           V
 	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-	// | | | | | | | | | | | | | | | | |  m_mask = 0xf
+	// | | | | | | | | | | | | | | | | |  mask = (m_capacity-1)
 	// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 	//  ^
 	//  |
@@ -93,6 +94,10 @@ namespace libtorrent
 		index_type span() const
 		{ return (m_last - m_first) & 0xffff; }
 
+#ifdef TORRENT_DEBUG
+		void check_invariant() const;
+#endif
+
 	private:
 		void** m_storage;
 		std::size_t m_capacity;

src/packet_buffer.cpp

@@ -33,6 +33,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include <stdlib.h> // free and calloc
 #include "libtorrent/packet_buffer.hpp"
 #include "libtorrent/assert.hpp"
+#include "libtorrent/invariant_check.hpp"
 
 namespace libtorrent {
 
@@ -47,6 +48,18 @@ namespace libtorrent {
 		, m_last(0)
 	{}
 
+#ifdef TORRENT_DEBUG
+	void packet_buffer::check_invariant() const
+	{
+		int count = 0;
+		for (int i = 0; i < m_capacity; ++i)
+		{
+			count += m_storage[i] ? 1 : 0;
+		}
+		TORRENT_ASSERT(count == m_size);
+	}
+#endif
+
 	packet_buffer::~packet_buffer()
 	{
 		free(m_storage);
@@ -54,10 +67,14 @@ namespace libtorrent {
 
 	void* packet_buffer::insert(index_type idx, void* value)
 	{
+		INVARIANT_CHECK;
+
 		TORRENT_ASSERT_VAL(idx <= 0xffff, idx);
 		// you're not allowed to insert NULLs!
 		TORRENT_ASSERT(value);
 
+		if (value == 0) return remove(idx);
+
 		if (m_size != 0)
 		{
 			if (compare_less_wrap(idx, m_first, 0xffff))
@@ -117,6 +134,7 @@ namespace libtorrent {
 
 	void* packet_buffer::at(index_type idx) const
 	{
+		INVARIANT_CHECK;
 		if (idx >= m_first + m_capacity)
 			return 0;
 
@@ -125,11 +143,13 @@ namespace libtorrent {
 			return 0;
 		}
 
-		return m_storage[idx & (m_capacity - 1)];
+		const int mask = (m_capacity - 1);
+		return m_storage[idx & mask];
 	}
 
 	void packet_buffer::reserve(std::size_t size)
 	{
+		INVARIANT_CHECK;
 		TORRENT_ASSERT_VAL(size <= 0xffff, size);
 		std::size_t new_size = m_capacity == 0 ? 16 : m_capacity;
 
@@ -152,6 +172,7 @@ namespace libtorrent {
 
 	void* packet_buffer::remove(index_type idx)
 	{
+		INVARIANT_CHECK;
 		// TODO: use compare_less_wrap for this comparison as well
 		if (idx >= m_first + m_capacity)
 			return 0;
@@ -159,8 +180,9 @@ namespace libtorrent {
 		if (compare_less_wrap(idx, m_first, 0xffff))
 			return 0;
 
-		void* old_value = m_storage[idx & (m_capacity - 1)];
+		const int mask = (m_capacity - 1);
-		m_storage[idx & (m_capacity - 1)] = 0;
+		void* old_value = m_storage[idx & mask];
+		m_storage[idx & mask] = 0;
 
 		if (old_value)
 		{
@@ -170,13 +192,13 @@ namespace libtorrent {
 
 		if (idx == m_first && m_size != 0)
 		{
-			while (!m_storage[++m_first & (m_capacity - 1)]);
+			while (!m_storage[++m_first & mask]);
 			m_first &= 0xffff;
 		}
 
 		if (((idx + 1) & 0xffff) == m_last && m_size != 0)
 		{
-			while (!m_storage[--m_last & (m_capacity - 1)]);
+			while (!m_storage[--m_last & mask]);
 			++m_last;
 			m_last &= 0xffff;
 		}