AK: Add InputBitStream class.

2 files changed, 124 insertions, 0 deletions

diff --git a/AK/BitStream.h b/AK/BitStream.h
new file mode 100644
index 0000000000..83bf9fcaa8
--- /dev/null
+++ b/AK/BitStream.h
@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2020, the SerenityOS developers.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Optional.h>
+#include <AK/Stream.h>
+
+namespace AK {
+
+class InputBitStream final : public InputStream {
+public:
+    explicit InputBitStream(InputStream& stream)
+        : m_stream(stream)
+    {
+    }
+
+    size_t read(Bytes bytes) override
+    {
+        size_t nread = 0;
+
+        if (bytes.size() >= 1) {
+            if (m_next_byte.has_value()) {
+                bytes[0] = m_next_byte.value();
+                m_next_byte.clear();
+
+                ++nread;
+            }
+        }
+
+        return nread + m_stream.read(bytes.slice(nread));
+    }
+
+    bool read_or_error(Bytes bytes) override
+    {
+        if (read(bytes) != bytes.size()) {
+            m_error = true;
+            return false;
+        }
+
+        return true;
+    }
+
+    bool eof() const override { return !m_next_byte.has_value() && m_stream.eof(); }
+
+    bool discard_or_error(size_t count) override
+    {
+        if (count >= 1) {
+            if (m_next_byte.has_value()) {
+                m_next_byte.clear();
+                --count;
+            }
+        }
+
+        return discard_or_error(count);
+    }
+
+    u32 read_bits(size_t count)
+    {
+        u32 result = 0;
+
+        size_t nread = 0;
+        while (nread < count) {
+            if (m_next_byte.has_value()) {
+                const auto bit = (m_next_byte.value() >> m_bit_offset) & 1;
+                result |= bit << nread;
+                ++nread;
+
+                if (m_bit_offset++ == 7)
+                    m_next_byte.clear();
+            } else if (m_stream.eof()) {
+                m_error = true;
+                return 0;
+            } else {
+                m_stream >> m_next_byte;
+                m_bit_offset = 0;
+            }
+        }
+
+        return result;
+    }
+
+    bool read_bit() { return static_cast<bool>(read_bits(1)); }
+
+    void align_to_byte_boundary()
+    {
+        if (m_next_byte.has_value())
+            m_next_byte.clear();
+    }
+
+private:
+    Optional<u8> m_next_byte;
+    size_t m_bit_offset { 0 };
+    InputStream& m_stream;
+};
+
+}
+
+using AK::InputBitStream;
diff --git a/AK/Forward.h b/AK/Forward.h
index baec79d5ad..1f2c47cd66 100644
--- a/AK/Forward.h
+++ b/AK/Forward.h
@@ -52,6 +52,7 @@ class InputStream;
 class InputMemoryStream;
 class DuplexMemoryStream;
 class OutputStream;
+class InputBitStream;
 
 template<size_t Capacity>
 class CircularDuplexStream;
@@ -138,6 +139,7 @@ using AK::Function;
 using AK::HashMap;
 using AK::HashTable;
 using AK::InlineLinkedList;
+using AK::InputBitStream;
 using AK::InputMemoryStream;
 using AK::InputStream;
 using AK::IPv4Address;