AK: Move the LEB128 logic to AK and make it usable with InputStream

AK/LEB128.h

@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2020-2021, the SerenityOS developers.
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Stream.h>
+#include <AK/Types.h>
+
+namespace AK {
+
+struct LEB128 {
+ template<typename StreamT>
+ static bool read_unsigned(StreamT& stream, size_t& result)
+ {
+ [[maybe_unused]] size_t backup_offset = 0;
+ if constexpr (requires { stream.offset(); })
+ backup_offset = stream.offset();
+ InputStream& input_stream { stream };
+
+ result = 0;
+ size_t num_bytes = 0;
+ while (true) {
+ if (input_stream.unreliable_eof()) {
+ if constexpr (requires { stream.seek(backup_offset); })
+ stream.seek(backup_offset);
+ input_stream.set_fatal_error();
+ return false;
+ }
+
+ u8 byte = 0;
+ input_stream >> byte;
+ if (input_stream.has_any_error())
+ return false;
+
+ result = (result) | (static_cast<size_t>(byte & ~(1 << 7)) << (num_bytes * 7));
+ if (!(byte & (1 << 7)))
+ break;
+ ++num_bytes;
+ }
+
+ return true;
+ }
+
+ template<typename StreamT>
+ static bool read_signed(StreamT& stream, ssize_t& result)
+ {
+ [[maybe_unused]] size_t backup_offset = 0;
+ if constexpr (requires { stream.offset(); })
+ backup_offset = stream.offset();
+ InputStream& input_stream { stream };
+
+ result = 0;
+ size_t num_bytes = 0;
+ u8 byte = 0;
+
+ do {
+ if (input_stream.unreliable_eof()) {
+ if constexpr (requires { stream.seek(backup_offset); })
+ stream.seek(backup_offset);
+ input_stream.set_fatal_error();
+ return false;
+ }
+
+ input_stream >> byte;
+ if (input_stream.has_any_error())
+ return false;
+ result = (result) | (static_cast<size_t>(byte & ~(1 << 7)) << (num_bytes * 7));
+ ++num_bytes;
+ } while (byte & (1 << 7));
+
+ if (num_bytes * 7 < sizeof(size_t) * 4 && (byte & 0x40)) {
+ // sign extend
+ result |= ((size_t)(-1) << (num_bytes * 7));
+ }
+
+ return true;
+ }
+};
+
+}
+
+using AK::LEB128;

AK/MemoryStream.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <AK/ByteBuffer.h>
+#include <AK/LEB128.h>
 #include <AK/MemMem.h>
 #include <AK/Stream.h>
 #include <AK/Vector.h>
@@ -73,58 +74,9 @@ class InputMemoryStream final : public InputStream {
  return m_bytes[m_offset];
  }
 
- bool read_LEB128_unsigned(size_t& result)
- {
- const auto backup = m_offset;
-
- result = 0;
- size_t num_bytes = 0;
- while (true) {
- if (eof()) {
- m_offset = backup;
- set_recoverable_error();
- return false;
- }
-
- const u8 byte = m_bytes[m_offset];
- result = (result) | (static_cast<size_t>(byte & ~(1 << 7)) << (num_bytes * 7));
- ++m_offset;
- if (!(byte & (1 << 7)))
- break;
- ++num_bytes;
- }
-
- return true;
- }
-
- bool read_LEB128_signed(ssize_t& result)
- {
- const auto backup = m_offset;
-
- result = 0;
- size_t num_bytes = 0;
- u8 byte = 0;
-
- do {
- if (eof()) {
- m_offset = backup;
- set_recoverable_error();
- return false;
- }
-
- byte = m_bytes[m_offset];
- result = (result) | (static_cast<size_t>(byte & ~(1 << 7)) << (num_bytes * 7));
- ++m_offset;
- ++num_bytes;
- } while (byte & (1 << 7));
+ bool read_LEB128_unsigned(size_t& result) { return LEB128::read_unsigned(*this, result); }
 
- if (num_bytes * 7 < sizeof(size_t) * 4 && (byte & 0x40)) {
- // sign extend
- result |= ((size_t)(-1) << (num_bytes * 7));
- }
-
- return true;
- }
+ bool read_LEB128_signed(ssize_t& result) { return LEB128::read_signed(*this, result); }
 
  ReadonlyBytes bytes() const { return m_bytes; }
  size_t offset() const { return m_offset; }