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/xtea.h

@@ -3,7 +3,7 @@
  *
  * \brief XTEA block cipher (32-bit)
  *
- *  Copyright (C) 2006-2010, Brainspark B.V.
+ *  Copyright (C) 2006-2013, 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_XTEA_H
 #define POLARSSL_XTEA_H
 
+#include "config.h"
+
 #include <string.h>
 
 #ifdef _MSC_VER
@@ -41,6 +43,10 @@ typedef UINT32 uint32_t;
 
 #define POLARSSL_ERR_XTEA_INVALID_INPUT_LENGTH             -0x0028  /**< The data input has an invalid length. */
 
+#if !defined(POLARSSL_XTEA_ALT)
+// Regular implementation
+//
+
 /**
  * \brief          XTEA context structure
  */
@@ -97,6 +103,18 @@ int xtea_crypt_cbc( xtea_context *ctx,
                     unsigned char *input,
                     unsigned char *output);
 
+#ifdef __cplusplus
+}
+#endif
+
+#else  /* POLARSSL_XTEA_ALT */
+#include "xtea_alt.h"
+#endif /* POLARSSL_XTEA_ALT */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * \brief          Checkup routine
  *