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/*
* Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>.
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/ByteBuffer.h>
#include <AK/Concepts.h>
#include <AK/Error.h>
#include <AK/NonnullOwnPtr.h>
#include <AK/NonnullRefPtr.h>
#include <AK/OwnPtr.h>
#include <AK/Span.h>
#include <AK/StdLibExtraDetails.h>
#include <AK/Types.h>
#include <LibCore/Stream.h>
namespace Core::Stream {
/// A stream wrapper class that allows you to read arbitrary amounts of bits
/// in big-endian order from another stream.
/// Note that this stream does not own its underlying stream, it merely takes a reference.
class BigEndianInputBitStream : public Stream {
public:
static ErrorOr<NonnullOwnPtr<BigEndianInputBitStream>> construct(Stream& stream)
{
return adopt_nonnull_own_or_enomem<BigEndianInputBitStream>(new BigEndianInputBitStream(stream));
}
// ^Stream
virtual bool is_readable() const override { return m_stream.is_readable(); }
virtual ErrorOr<size_t> read(Bytes bytes) override
{
if (m_current_byte.has_value() && is_aligned_to_byte_boundary()) {
bytes[0] = m_current_byte.release_value();
return m_stream.read(bytes.slice(1));
}
align_to_byte_boundary();
return m_stream.read(bytes);
}
virtual bool is_writable() const override { return m_stream.is_writable(); }
virtual ErrorOr<size_t> write(ReadonlyBytes bytes) override { return m_stream.write(bytes); }
virtual bool write_or_error(ReadonlyBytes bytes) override { return m_stream.write_or_error(bytes); }
virtual bool is_eof() const override { return m_stream.is_eof() && !m_current_byte.has_value(); }
virtual bool is_open() const override { return m_stream.is_open(); }
virtual void close() override
{
m_stream.close();
align_to_byte_boundary();
}
ErrorOr<bool> read_bit()
{
return read_bits<bool>(1);
}
/// Depending on the number of bits to read, the return type can be chosen appropriately.
/// This avoids a bunch of static_cast<>'s for the user.
// TODO: Support u128, u256 etc. as well: The concepts would be quite complex.
template<Unsigned T = u64>
ErrorOr<T> read_bits(size_t count)
{
if constexpr (IsSame<bool, T>) {
VERIFY(count == 1);
}
T result = 0;
size_t nread = 0;
while (nread < count) {
if (m_current_byte.has_value()) {
if constexpr (!IsSame<bool, T> && !IsSame<u8, T>) {
// read as many bytes as possible directly
if (((count - nread) >= 8) && is_aligned_to_byte_boundary()) {
// shift existing data over
result <<= 8;
result |= m_current_byte.value();
nread += 8;
m_current_byte.clear();
} else {
const auto bit = (m_current_byte.value() >> (7 - m_bit_offset)) & 1;
result <<= 1;
result |= bit;
++nread;
if (m_bit_offset++ == 7)
m_current_byte.clear();
}
} else {
// Always take this branch for booleans or u8: there's no purpose in reading more than a single bit
const auto bit = (m_current_byte.value() >> (7 - m_bit_offset)) & 1;
if constexpr (IsSame<bool, T>)
result = bit;
else {
result <<= 1;
result |= bit;
}
++nread;
if (m_bit_offset++ == 7)
m_current_byte.clear();
}
} else {
// FIXME: This returns Optional so TRY is not useable
auto temp_buffer = ByteBuffer::create_uninitialized(1);
if (!temp_buffer.has_value())
return Error::from_string_literal("Couldn't allocate temporary byte buffer"sv);
TRY(m_stream.read(temp_buffer->bytes()));
m_current_byte = (*temp_buffer)[0];
m_bit_offset = 0;
}
}
return result;
}
/// Discards any sub-byte stream positioning the input stream may be keeping track of.
/// Non-bitwise reads will implicitly call this.
void align_to_byte_boundary()
{
m_current_byte.clear();
m_bit_offset = 0;
}
/// Whether we are (accidentally or intentionally) at a byte boundary right now.
ALWAYS_INLINE bool is_aligned_to_byte_boundary() const { return m_bit_offset == 0; }
private:
BigEndianInputBitStream(Stream& stream)
: m_stream(stream)
{
}
Optional<u8> m_current_byte;
size_t m_bit_offset { 0 };
Stream& m_stream;
};
}
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