Initial community commit

Src/external_dependencies/openmpt-trunk/soundlib/BitReader.h

@@ -0,0 +1,82 @@
+/*
+ * BitReader.h
+ * -----------
+ * Purpose: An extended FileReader to read bit-oriented rather than byte-oriented streams.
+ * Notes  : The current implementation can only read bit widths up to 32 bits, and it always
+ *          reads bits starting from the least significant bit, as this is all that is
+ *          required by the class users at the moment.
+ * Authors: OpenMPT Devs
+ * The OpenMPT source code is released under the BSD license. Read LICENSE for more details.
+ */
+
+
+#pragma once
+
+#include "openmpt/all/BuildSettings.hpp"
+
+#include "../common/FileReader.h"
+#include <stdexcept>
+#include "mpt/io/base.hpp"
+
+
+OPENMPT_NAMESPACE_BEGIN
+
+
+class BitReader : private FileReader
+{
+protected:
+	off_t m_bufPos = 0, m_bufSize = 0;
+	uint32 bitBuf = 0; // Current bit buffer
+	int m_bitNum = 0;  // Currently available number of bits
+	std::byte buffer[mpt::IO::BUFFERSIZE_TINY]{};
+
+public:
+
+	class eof : public std::range_error
+	{
+	public:
+		eof() : std::range_error("Truncated bit buffer") { }
+	};
+
+	BitReader() : FileReader() { }
+	BitReader(mpt::span<const std::byte> bytedata) : FileReader(bytedata) { }
+	BitReader(const FileCursor &other) : FileReader(other) { }
+	BitReader(FileCursor &&other) : FileReader(std::move(other)) { }
+
+	off_t GetLength() const
+	{
+		return FileReader::GetLength();
+	}
+
+	off_t GetPosition() const
+	{
+		return FileReader::GetPosition() - m_bufSize + m_bufPos;
+	}
+
+	uint32 ReadBits(int numBits)
+	{
+		while(m_bitNum < numBits)
+		{
+			// Fetch more bits
+			if(m_bufPos >= m_bufSize)
+			{
+				m_bufSize = ReadRaw(mpt::as_span(buffer)).size();
+				m_bufPos = 0;
+				if(!m_bufSize)
+				{
+					throw eof();
+				}
+			}
+			bitBuf |= (static_cast<uint32>(buffer[m_bufPos++]) << m_bitNum);
+			m_bitNum += 8;
+		}
+
+		uint32 v = bitBuf & ((1 << numBits) - 1);
+		bitBuf >>= numBits;
+		m_bitNum -= numBits;
+		return v;
+	}
+};
+
+
+OPENMPT_NAMESPACE_END