Add some bit utils and initial l77 encoder.

src/core/streams/BitStream.cpp

@@ -0,0 +1,56 @@
+#include "BitStream.h"
+
+#include "ByteUtils.h"
+
+bool BitStream::loadNextByte()
+{
+    if (mByteOffset + 1 == mBuffer.size())
+    {
+        return false;
+    }
+    else
+    {
+        mByteOffset++;
+        mCurrentByte = mBuffer[mByteOffset];
+        return true;
+    }
+}
+
+bool BitStream::getNextNBits(unsigned n, unsigned char& buffer)
+{
+    int overshoot = n + mBitOffset - 7;
+
+    if (overshoot > 0)
+    {
+        unsigned char last_byte = mCurrentByte;
+        if (!loadNextByte())
+        {
+            return false;
+        }
+
+        auto num_lower = 7 - mBitOffset;
+        char lower_bits = ByteUtils::getHigherNBits(last_byte, num_lower);
+        char higher_bits = ByteUtils::getLowerNBits(mCurrentByte, overshoot);
+
+        buffer = (higher_bits << (8 - num_lower)) | (lower_bits >> mBitOffset);
+
+        mBitOffset = overshoot;
+        return true;
+    }
+    else
+    {
+        buffer = ByteUtils::getMBitsAtN(mCurrentByte, n, mBitOffset);
+        mBitOffset += n;
+        return true;
+    }
+}
+
+void BitStream::setByte(unsigned idx, unsigned char data)
+{
+    mBuffer[idx] = data;
+}
+
+void BitStream::setBufferSize(std::size_t size)
+{
+    mBuffer = std::vector<unsigned char>(size);
+}