Added mechanism to provide alternative cipher / hash implementations

All symmetric cipher algorithms and hash algorithms now include support
for a POLARSSL_XXX_ALT flag that prevents the definition of the
algorithm context structure and all 'core' functions.

include/polarssl/blowfish.h

@@ -3,7 +3,7 @@
  *
  * \brief Blowfish block cipher
  *
- *  Copyright (C) 2012-2012, Brainspark B.V.
+ *  Copyright (C) 2012-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
@@ -27,6 +27,8 @@
 #ifndef POLARSSL_BLOWFISH_H
 #define POLARSSL_BLOWFISH_H
 
+#include "config.h"
+
 #include <string.h>
 
 #ifdef _MSC_VER
@@ -46,6 +48,10 @@ typedef UINT32 uint32_t;
 #define POLARSSL_ERR_BLOWFISH_INVALID_KEY_LENGTH                -0x0016  /**< Invalid key length. */
 #define POLARSSL_ERR_BLOWFISH_INVALID_INPUT_LENGTH              -0x0018  /**< Invalid data input length. */
 
+#if !defined(POLARSSL_BLOWFISH_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          Blowfish context structure
  */
@@ -158,4 +164,8 @@ int blowfish_crypt_ctr( blowfish_context *ctx,
 }
 #endif
 
+#else  /* POLARSSL_BLOWFISH_ALT */
+#include "blowfish_alt.h"
+#endif /* POLARSSL_BLOWFISH_ALT */
+
 #endif /* blowfish.h */