Class helping with assembling data from chunks of byte unaligned bit arrays.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@31629 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/apps/debugger/util/BitBuffer.cpp

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
+ * Distributed under the terms of the MIT License.
+ */
+
+
+#include "BitBuffer.h"
+
+
+// #pragma mark - BitReader
+
+
+struct BitBuffer::BitReader {
+	const uint8*	data;
+	uint64			bitSize;
+	uint32			bitOffset;
+
+	BitReader(const uint8* data, uint64 bitSize, uint32 bitOffset)
+		:
+		data(data),
+		bitSize(bitSize),
+		bitOffset(bitOffset)
+	{
+	}
+
+	uint8 ReadByte()
+	{
+		uint8 byte = *data;
+		data++;
+		bitSize -= 8;
+
+		if (bitOffset == 0)
+			return byte;
+
+		return (byte << bitOffset) | (*data >> (8 - bitOffset));
+	}
+
+	uint8 ReadBits(uint32 count)
+	{
+		uint8 byte = *data;
+		bitSize -= count;
+		bitOffset += count;
+
+		if (bitOffset <= 8) {
+			if (bitOffset == 8) {
+				bitOffset = 0;
+				data++;
+				return byte & ((1 << count) - 1);
+			}
+
+			return (byte >> (8 - bitOffset)) & ((1 << count) - 1);
+		}
+
+		data++;
+		bitOffset -= 8;
+		return ((byte << bitOffset) | (*data >> (8 - bitOffset)))
+			& ((1 << count) - 1);
+	}
+};
+
+
+// #pragma mark - BitBuffer
+
+
+BitBuffer::BitBuffer()
+	:
+	fMissingBits(0)
+{
+}
+
+
+BitBuffer::~BitBuffer()
+{
+}
+
+
+bool
+BitBuffer::AddBytes(const void* data, size_t size)
+{
+	if (size == 0)
+		return true;
+
+	if (fMissingBits == 0) {
+		size_t oldSize = fBytes.Size();
+		if (!fBytes.AddUninitialized(size))
+			return false;
+
+		memcpy(fBytes.Elements() + oldSize, data, size);
+		return true;
+	}
+
+	return AddBits(data, (uint64)size * 8, 0);
+}
+
+
+bool
+BitBuffer::AddBits(const void* _data, uint64 bitSize, uint32 bitOffset)
+{
+	if (bitSize == 0)
+		return true;
+
+	const uint8* data = (const uint8*)_data + bitOffset / 8;
+	bitOffset %= 8;
+
+	BitReader reader(data, bitSize, bitOffset);
+
+	// handle special case first: no more bits than missing
+	size_t oldSize = fBytes.Size();
+	if (fMissingBits > 0 && bitSize <= fMissingBits) {
+		fMissingBits -= bitSize;
+		uint8 bits = reader.ReadBits(bitSize) << fMissingBits;
+		fBytes[oldSize - 1] |= bits;
+		return true;
+	}
+
+	// resize the buffer
+	if (!fBytes.AddUninitialized((reader.bitSize - fMissingBits + 7) / 8))
+		return false;
+
+	// fill in missing bits
+	if (fMissingBits > 0) {
+		fBytes[oldSize - 1] |= reader.ReadBits(fMissingBits);
+		fMissingBits = 0;
+	}
+
+	// read full bytes as long as we can
+	uint8* buffer = fBytes.Elements() + oldSize;
+	while (reader.bitSize >= 8) {
+		*buffer = reader.ReadByte();
+		buffer++;
+	}
+
+	// If we have left-over bits, write a partial byte.
+	if (reader.bitSize > 0) {
+		fMissingBits = 8 - reader.bitSize;
+		*buffer = reader.ReadBits(reader.bitSize) << fMissingBits;
+	}
+
+	return true;
+}

src/apps/debugger/util/BitBuffer.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
+ * Distributed under the terms of the MIT License.
+ */
+#ifndef BIT_BUFFER_H
+#define BIT_BUFFER_H
+
+
+#include <SupportDefs.h>
+
+
+#include "Array.h"
+
+
+class BitBuffer {
+public:
+								BitBuffer();
+								~BitBuffer();
+
+			bool				AddBytes(const void* data, size_t size);
+			bool				AddBits(const void* data, uint64 bitSize,
+									uint32 bitOffset = 0);
+
+			uint8*				Bytes() const	{ return fBytes.Elements(); }
+			size_t				Size() const	{ return fBytes.Size(); }
+			size_t				BitSize() const
+									{ return Size() * 8 - fMissingBits; }
+
+private:
+			struct BitReader;
+
+private:
+			Array<uint8>		fBytes;
+			uint8				fMissingBits;
+};
+
+
+#endif	// BIT_BUFFER_H