From 48260b50542f8c294cccc84d41803bd8d3568142 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Tue, 27 Apr 2021 00:09:02 +0430
Subject: [PATCH] AK: Move the LEB128 logic to AK and make it usable with
 InputStream

---
 AK/LEB128.h       | 85 +++++++++++++++++++++++++++++++++++++++++++++++
 AK/MemoryStream.h | 54 ++----------------------------
 2 files changed, 88 insertions(+), 51 deletions(-)
 create mode 100644 AK/LEB128.h

diff --git a/AK/LEB128.h b/AK/LEB128.h
new file mode 100644
index 0000000000..653d38a24e
--- /dev/null
+++ b/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;
diff --git a/AK/MemoryStream.h b/AK/MemoryStream.h
index f53792315a..4f92621800 100644
--- a/AK/MemoryStream.h
+++ b/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 @@ public:
         return m_bytes[m_offset];
     }
 
-    bool read_LEB128_unsigned(size_t& result)
-    {
-        const auto backup = m_offset;
+    bool read_LEB128_unsigned(size_t& result) { return LEB128::read_unsigned(*this, result); }
 
-        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));
-
-        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; }