1 files changed, 63 insertions, 0 deletions
diff --git a/extmod/uzlib/crc32.c b/extmod/uzlib/crc32.c
new file mode 100644
index 0000000000..8c9976594d
--- /dev/null
+++ b/extmod/uzlib/crc32.c
@@ -0,0 +1,63 @@
+/*
+ * CRC32 checksum
+ *
+ * Copyright (c) 1998-2003 by Joergen Ibsen / Jibz
+ * All Rights Reserved
+ *
+ * http://www.ibsensoftware.com/
+ *
+ * This software is provided 'as-is', without any express
+ * or implied warranty.  In no event will the authors be
+ * held liable for any damages arising from the use of
+ * this software.
+ *
+ * Permission is granted to anyone to use this software
+ * for any purpose, including commercial applications,
+ * and to alter it and redistribute it freely, subject to
+ * the following restrictions:
+ *
+ * 1. The origin of this software must not be
+ *    misrepresented; you must not claim that you
+ *    wrote the original software. If you use this
+ *    software in a product, an acknowledgment in
+ *    the product documentation would be appreciated
+ *    but is not required.
+ *
+ * 2. Altered source versions must be plainly marked
+ *    as such, and must not be misrepresented as
+ *    being the original software.
+ *
+ * 3. This notice may not be removed or altered from
+ *    any source distribution.
+ */
+
+/*
+ * CRC32 algorithm taken from the zlib source, which is
+ * Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
+ */
+
+#include "tinf.h"
+
+static const unsigned int tinf_crc32tab[16] = {
+   0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190,
+   0x6b6b51f4, 0x4db26158, 0x5005713c, 0xedb88320, 0xf00f9344,
+   0xd6d6a3e8, 0xcb61b38c, 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278,
+   0xbdbdf21c
+};
+
+/* crc is previous value for incremental computation, 0xffffffff initially */
+unsigned int uzlib_crc32(const void *data, unsigned int length, unsigned int crc)
+{
+   const unsigned char *buf = (const unsigned char *)data;
+   unsigned int i;
+
+   for (i = 0; i < length; ++i)
+   {
+      crc ^= buf[i];
+      crc = tinf_crc32tab[crc & 0x0f] ^ (crc >> 4);
+      crc = tinf_crc32tab[crc & 0x0f] ^ (crc >> 4);
+   }
+
+   // return value suitable for passing in next time, for final value invert it
+   return crc/* ^ 0xffffffff*/;
+}