AK: Add OutputBitStream class

This will be used in the deflate compressor.

1 files changed, 80 insertions, 0 deletions

diff --git a/AK/BitStream.h b/AK/BitStream.h
index fbb26d2b5c..8e509dd5fe 100644
--- a/AK/BitStream.h
+++ b/AK/BitStream.h
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020, the SerenityOS developers.
+ * Copyright (c) 2021, Idan Horowitz <idan.horowitz@gmail.com>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -121,6 +122,85 @@ private:
     InputStream& m_stream;
 };
 
+class OutputBitStream final : public OutputStream {
+public:
+    explicit OutputBitStream(OutputStream& stream)
+        : m_stream(stream)
+    {
+    }
+
+    // WARNING: write aligns to the next byte boundary before writing, if unaligned writes are needed this should be rewritten
+    size_t write(ReadonlyBytes bytes) override
+    {
+        if (has_any_error())
+            return 0;
+        align_to_byte_boundary();
+        if (has_fatal_error()) // if align_to_byte_boundary failed
+            return 0;
+        return m_stream.write(bytes);
+    }
+
+    bool write_or_error(ReadonlyBytes bytes) override
+    {
+        if (write(bytes) < bytes.size()) {
+            set_fatal_error();
+            return false;
+        }
+        return true;
+    }
+
+    void write_bits(u32 bits, size_t count)
+    {
+        VERIFY(count <= 32);
+        size_t n_written = 0;
+        while (n_written < count) {
+            if (m_stream.has_any_error()) {
+                set_fatal_error();
+                return;
+            }
+
+            if (m_next_byte.has_value()) {
+                m_next_byte.value() |= ((bits >> n_written) & 1) << m_bit_offset;
+                ++n_written;
+
+                if (m_bit_offset++ == 7) {
+                    m_stream << m_next_byte.value();
+                    m_next_byte.clear();
+                }
+            } else {
+                m_bit_offset = 0;
+                m_next_byte = 0;
+            }
+        }
+    }
+
+    void write_bit(bool bit)
+    {
+        write_bits(bit, 1);
+    }
+
+    void align_to_byte_boundary()
+    {
+        if (m_next_byte.has_value()) {
+            if (!m_stream.write_or_error(ReadonlyBytes { &m_next_byte.value(), 1 })) {
+                set_fatal_error();
+            }
+            m_next_byte.clear();
+        }
+    }
+
+    size_t bit_offset() const
+    {
+        return m_bit_offset;
+    }
+
+private:
+    Optional<u8> m_next_byte;
+    size_t m_bit_offset { 0 };
+    OutputStream& m_stream;
+};
+
 }
 
 using AK::InputBitStream;
+using AK::OutputBitStream;