1 files changed, 69 insertions, 0 deletions
diff --git a/src/CRC32.cpp b/src/CRC32.cpp
new file mode 100644
index 0000000..62e334f
--- /dev/null
+++ b/src/CRC32.cpp
@@ -0,0 +1,69 @@
+/*
+    Copyright 2016-2019 StapleButter
+
+    This file is part of melonDS.
+
+    melonDS is free software: you can redistribute it and/or modify it under
+    the terms of the GNU General Public License as published by the Free
+    Software Foundation, either version 3 of the License, or (at your option)
+    any later version.
+
+    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with melonDS. If not, see http://www.gnu.org/licenses/.
+*/
+
+#include "CRC32.h"
+
+// http://www.codeproject.com/KB/recipes/crc32_large.aspx
+
+u32 crctable[256];
+bool tableinited = false;
+
+u32 _reflect(u32 refl, char ch)
+{
+    u32 value = 0;
+
+    for(int i = 1; i < (ch + 1); i++)
+    {
+        if (refl & 1)
+            value |= 1 << (ch - i);
+        refl >>= 1;
+    }
+
+	return value;
+}
+
+void _inittable()
+{
+	u32 polynomial = 0x04C11DB7;
+
+	for (int i = 0; i < 0x100; i++)
+    {
+        crctable[i] = _reflect(i, 8) << 24;
+
+        for (int j = 0; j < 8; j++)
+            crctable[i] = (crctable[i] << 1) ^ (crctable[i] & (1 << 31) ? polynomial : 0);
+
+        crctable[i] = _reflect(crctable[i],  32);
+    }
+}
+
+u32 CRC32(u8 *data, int len)
+{
+    if (!tableinited)
+    {
+        _inittable();
+        tableinited = true;
+    }
+
+	u32 crc = 0xFFFFFFFF;
+
+	while (len--)
+        crc = (crc >> 8) ^ crctable[(crc & 0xFF) ^ *data++];
+
+	return (crc ^ 0xFFFFFFFF);
+}