Add common feature unavailable error

Add a common error for the feature unavailable, in the
platform module.

Author: Ron Eldor

include/mbedtls/error.h

@@ -80,7 +80,7 @@
  * CHACHA20  3                  0x0051-0x0055
  * POLY1305  3                  0x0057-0x005B
  * CHACHAPOLY 2 0x0054-0x0056
- * PLATFORM  1  0x0070-0x0070
+ * PLATFORM  1  0x0070-0x0072
  *
  * High-level module nr (3 bits - 0x0...-0x7...)
  * Name      ID  Nr of Errors

include/mbedtls/platform.h

@@ -43,7 +43,8 @@
 #include "platform_time.h"
 #endif
 
-#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED       -0x0070 /**< Hardware accelerator failed */
+#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED     -0x0070 /**< Hardware accelerator failed */
+#define MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED -0x0072 /**< The requested feature is not supported by the platform */
 
 #ifdef __cplusplus
 extern "C" {

library/error.c

@@ -834,6 +834,8 @@ void mbedtls_strerror( int ret, char *buf, size_t buflen )
 #if defined(MBEDTLS_PLATFORM_C)
     if( use_ret == -(MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED) )
         mbedtls_snprintf( buf, buflen, "PLATFORM - Hardware accelerator failed" );
+    if( use_ret == -(MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED) )
+        mbedtls_snprintf( buf, buflen, "PLATFORM - The requested feature is not supported by the platform" );
 #endif /* MBEDTLS_PLATFORM_C */
 
 #if defined(MBEDTLS_POLY1305_C)