[crypto] Replace MD5 implementation

Replace MD5 implementation with one which is around 20% smaller.  This
implementation has been verified using the existing MD5 self-tests.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/md5.h

@@ -1,23 +1,72 @@
 #ifndef _IPXE_MD5_H
 #define _IPXE_MD5_H
 
+/** @file
+ *
+ * MD5 algorithm
+ *
+ */
+
 FILE_LICENCE ( GPL2_OR_LATER );
 
-struct digest_algorithm;
-
 #include <stdint.h>
+#include <ipxe/crypto.h>
 
-#define MD5_DIGEST_SIZE		16
-#define MD5_BLOCK_WORDS		16
-#define MD5_HASH_WORDS		4
-
-struct md5_ctx {
-	u32 hash[MD5_HASH_WORDS];
-	u32 block[MD5_BLOCK_WORDS];
-	u64 byte_count;
+/** An MD5 digest */
+struct md5_digest {
+	/** Hash output */
+	uint32_t h[4];
 };
 
-#define MD5_CTX_SIZE sizeof ( struct md5_ctx )
+/** An MD5 data block */
+union md5_block {
+	/** Raw bytes */
+	uint8_t byte[64];
+	/** Raw dwords */
+	uint32_t dword[16];
+	/** Final block structure */
+	struct {
+		/** Padding */
+		uint8_t pad[56];
+		/** Length in bits */
+		uint64_t len;
+	} final;
+};
+
+/** MD5 digest and data block
+ *
+ * The order of fields within this structure is designed to minimise
+ * code size.
+ */
+struct md5_digest_data {
+	/** Digest of data already processed */
+	struct md5_digest digest;
+	/** Accumulated data */
+	union md5_block data;
+} __attribute__ (( packed ));
+
+/** MD5 digest and data block */
+union md5_digest_data_dwords {
+	/** Digest and data block */
+	struct md5_digest_data dd;
+	/** Raw dwords */
+	uint32_t dword[ sizeof ( struct md5_digest_data ) /
+			sizeof ( uint32_t ) ];
+};
+
+/** An MD5 context */
+struct md5_context {
+	/** Amount of accumulated data */
+	size_t len;
+	/** Digest and accumulated data */
+	union md5_digest_data_dwords ddd;
+} __attribute__ (( packed ));
+
+/** MD5 context size */
+#define MD5_CTX_SIZE sizeof ( struct md5_context )
+
+/** MD5 digest size */
+#define MD5_DIGEST_SIZE sizeof ( struct md5_digest )
 
 extern struct digest_algorithm md5_algorithm;