Introduce LTC_ALIGNED_BUF_SIZE(). [skip ci]

Since there's absolutely no way to ensure that a struct is somehow
aligned -- all those compile-time mechanism are best-effort and no
guarantee -- we align the necessary buffers at run-time.

AES-NI already introduced that, let's improve a bit upon its usage.

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

Author: sjaeckel

src/headers/tomcrypt_cipher.h

@@ -35,7 +35,7 @@ struct saferp_key {
 
 #ifdef LTC_RIJNDAEL
 struct rijndael_key {
-   unsigned char K[(60 + 60 + 4) * sizeof(ulong32)];
+   unsigned char K[LTC_ALIGNED_BUF_SIZE(ulong32, 60 + 60, 16)];
    ulong32 *eK;
    ulong32 *dK;
    int Nr;

src/headers/tomcrypt_macros.h

@@ -453,6 +453,11 @@ static inline ulong64 ROR64(ulong64 word, int i)
    #define LTC_UNUSED_PARAM(x) (void)(x)
 #endif
 
+/* Calculates the number of bytes required to hold a buffer that will later on be
+ * aligned by using LTC_ALIGN_BUF().
+ */
+#define LTC_ALIGNED_BUF_SIZE(type, n, align) (((n) + ((align)/sizeof(type))) * sizeof(type))
+
 /* there is no snprintf before Visual C++ 2015 */
 #if defined(_MSC_VER) && _MSC_VER < 1900
 #define snprintf _snprintf

src/headers/tomcrypt_private.h

@@ -33,7 +33,7 @@ LTC_STATIC_ASSERT(correct_ltc_uintptr_size, sizeof(ltc_uintptr) == sizeof(void*)
 /* Aligns a `unsigned char` buffer `buf` to `n` bytes and returns that aligned address.
  * Make sure that the buffer that is passed is huge enough.
  */
-#define LTC_ALIGN_BUF(buf, n) ((void*)((ltc_uintptr)&((unsigned char*)(buf))[n - 1] & (~(CONSTPTR(n) - CONSTPTR(1)))))
+#define LTC_ALIGN_BUF(buf, align) ((void*)((ltc_uintptr)&((unsigned char*)(buf))[(align) - 1] & (~(CONSTPTR(align) - CONSTPTR(1)))))
 
 #define LTC_OID_MAX_STRLEN 256