Implement byte reading macros into library/

To improve readability by saving horizontal and vertical space.
Removed unecessary & 0xFF.
Byte reading macros implemented in library/common.h, All files
containing "& 0xff" were modified.
Comments/Documentation not yet added to the macro definitions.

Fixes #4274

Signed-off-by: Joe Subbiani <joe.subbiani@arm.com>

library/common.h

@@ -50,4 +50,21 @@
 #define MBEDTLS_STATIC_TESTABLE static
 #endif
 
+/** Allow library to access its structs' private members.
+ *
+ * Although structs defined in header files are publicly available,
+ * their members are private and should not be accessed by the user.
+ */
+#define MBEDTLS_ALLOW_PRIVATE_ACCESS
+
+/** Byte Reading Macros
+ * 
+ * To tidy up code and save horizontal and vertical space, use byte 
+ * reading macros to cast
+ */
+#define BYTE_0( x ) ( (uint8_t) ( ( x ) & 0xff )  )
+#define BYTE_1( x ) ( (uint8_t) ( ( ( x ) >> 8 ) & 0xff )  )
+#define BYTE_2( x ) ( (uint8_t) ( ( ( x ) >> 16 ) & 0xff ) )
+#define BYTE_3( x ) ( (uint8_t) ( ( ( x ) >> 24 ) & 0xff ) )
+
 #endif /* MBEDTLS_LIBRARY_COMMON_H */

library/ctr_drbg.c

@@ -152,10 +152,10 @@ static int block_cipher_df( unsigned char *output,
      *     (Total is padded to a multiple of 16-bytes with zeroes)
      */
     p = buf + MBEDTLS_CTR_DRBG_BLOCKSIZE;
-    *p++ = ( data_len >> 24 ) & 0xff;
+    *p++ = BYTE_3( data_len );
-    *p++ = ( data_len >> 16 ) & 0xff;
+    *p++ = BYTE_2( data_len );
-    *p++ = ( data_len >> 8  ) & 0xff;
+    *p++ = BYTE_1( data_len );
-    *p++ = ( data_len       ) & 0xff;
+    *p++ = BYTE_0( data_len );
     p += 3;
     *p++ = MBEDTLS_CTR_DRBG_SEEDLEN;
     memcpy( p, data, data_len );

library/nist_kw.c

@@ -169,7 +169,7 @@ static void calc_a_xor_t( unsigned char A[KW_SEMIBLOCK_LENGTH], uint64_t t )
     size_t i = 0;
     for( i = 0; i < sizeof( t ); i++ )
     {
-        A[i] ^= ( t >> ( ( sizeof( t ) - 1 - i ) * 8 ) ) & 0xff;
+        A[i] ^= BYTE_0( t >> ( ( sizeof( t ) - 1 - i ) * 8 ) );
     }
 }
 

library/psa_crypto.c

@@ -4570,8 +4570,8 @@ static psa_status_t psa_tls12_prf_psk_to_ms_set_key(
      * uint16 with the value N, and the PSK itself.
      */
 
-    *cur++ = ( data_length >> 8 ) & 0xff;
+    *cur++ = BYTE_1( data_length );
-    *cur++ = ( data_length >> 0 ) & 0xff;
+    *cur++ = BYTE_0( data_length );
     memset( cur, 0, data_length );
     cur += data_length;
     *cur++ = pms[0];

library/psa_its_file.c

@@ -195,14 +195,14 @@ psa_status_t psa_its_set( psa_storage_uid_t uid,
     size_t n;
 
     memcpy( header.magic, PSA_ITS_MAGIC_STRING, PSA_ITS_MAGIC_LENGTH );
-    header.size[0] = data_length & 0xff;
+    header.size[0] = BYTE_0( data_length );
-    header.size[1] = ( data_length >> 8 ) & 0xff;
+    header.size[1] = BYTE_1( data_length );
-    header.size[2] = ( data_length >> 16 ) & 0xff;
+    header.size[2] = BYTE_2( data_length );
-    header.size[3] = ( data_length >> 24 ) & 0xff;
+    header.size[3] = BYTE_3( data_length );
-    header.flags[0] = create_flags & 0xff;
+    header.flags[0] = BYTE_0( create_flags );
-    header.flags[1] = ( create_flags >> 8 ) & 0xff;
+    header.flags[1] = BYTE_1( create_flags );
-    header.flags[2] = ( create_flags >> 16 ) & 0xff;
+    header.flags[2] = BYTE_2( create_flags );
-    header.flags[3] = ( create_flags >> 24 ) & 0xff;
+    header.flags[3] = BYTE_3( create_flags );
 
     psa_its_fill_filename( uid, filename );
     stream = fopen( PSA_ITS_STORAGE_TEMP, "wb" );

library/ssl_msg.c

@@ -2525,14 +2525,14 @@ int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl )
              * copy beginning of headers then fill fragmentation fields.
              * Handshake headers: type(1) len(3) seq(2) f_off(3) f_len(3) */
             memcpy( ssl->out_msg, cur->p, 6 );
+            
+            ssl->out_msg[6] = BYTE_2( frag_off );
+            ssl->out_msg[7] = BYTE_1( frag_off );
+            ssl->out_msg[8] = BYTE_0( frag_off );
 
-            ssl->out_msg[6] = ( ( frag_off >> 16 ) & 0xff );
+            ssl->out_msg[ 9] = BYTE_2( cur_hs_frag_len );
-            ssl->out_msg[7] = ( ( frag_off >>  8 ) & 0xff );
+            ssl->out_msg[10] = BYTE_1( cur_hs_frag_len );
-            ssl->out_msg[8] = ( ( frag_off       ) & 0xff );
+            ssl->out_msg[11] = BYTE_0( cur_hs_frag_len );
-
-            ssl->out_msg[ 9] = ( ( cur_hs_frag_len >> 16 ) & 0xff );
-            ssl->out_msg[10] = ( ( cur_hs_frag_len >>  8 ) & 0xff );
-            ssl->out_msg[11] = ( ( cur_hs_frag_len       ) & 0xff );
 
             MBEDTLS_SSL_DEBUG_BUF( 3, "handshake header", ssl->out_msg, 12 );
 

library/ssl_ticket.c

@@ -245,8 +245,8 @@ int mbedtls_ssl_ticket_write( void *p_ticket,
     {
          goto cleanup;
     }
-    state_len_bytes[0] = ( clear_len >> 8 ) & 0xff;
+    state_len_bytes[0] = BYTE_1( clear_len );
-    state_len_bytes[1] = ( clear_len      ) & 0xff;
+    state_len_bytes[1] = BYTE_0( clear_len );
 
     /* Encrypt and authenticate */
     if( ( ret = mbedtls_cipher_auth_encrypt_ext( &key->ctx,