add MD5 implementation

src/libFLAC/include/private/md5.h

@@ -0,0 +1,48 @@
+/*
+ * This is the header file for the MD5 message-digest algorithm.
+ * The algorithm is due to Ron Rivest.  This code was
+ * written by Colin Plumb in 1993, no copyright is claimed.
+ * This code is in the public domain; do with it what you wish.
+ *
+ * Equivalent code is available from RSA Data Security, Inc.
+ * This code has been tested against that, and is equivalent,
+ * except that you don't need to include two pages of legalese
+ * with every copy.
+ *
+ * To compute the message digest of a chunk of bytes, declare an
+ * MD5Context structure, pass it to MD5Init, call MD5Update as
+ * needed on buffers full of bytes, and then call MD5Final, which
+ * will fill a supplied 16-byte array with the digest.
+ *
+ * Changed so as no longer to depend on Colin Plumb's `usual.h'
+ * header definitions; now uses stuff from dpkg's config.h
+ *  - Ian Jackson <ijackson@nyx.cs.du.edu>.
+ * Still in the public domain.
+ *
+ * Josh Coalson: made some changes to integrate with libFLAC.
+ * Still in the public domain.
+ */
+
+#ifndef FLAC__PRIVATE__MD5_H
+#define FLAC__PRIVATE__MD5_H
+
+#define md5byte unsigned char
+
+#include "FLAC/ordinals.h"
+
+struct MD5Context {
+	uint32 buf[4];
+	uint32 bytes[2];
+	uint32 in[16];
+	byte *internal_buf;
+	unsigned capacity;
+};
+
+void MD5Init(struct MD5Context *context);
+void MD5Update(struct MD5Context *context, md5byte const *buf, unsigned len);
+void MD5Final(md5byte digest[16], struct MD5Context *context);
+void MD5Transform(uint32 buf[4], uint32 const in[16]);
+
+bool FLAC__MD5Accumulate(struct MD5Context *ctx, const int32 *signal[], unsigned channels, unsigned samples, unsigned bytes_per_sample);
+
+#endif /* !MD5_H */