Simplify some constant-time code
Some people recommend using bit operations to avoid the compiler producing a
branch on `ret != 0`, but:
- this makes the code less readable,
- here I got a warning from some compilers about unsigned unary minus
- and anyway modern compilers don't produce a branch here, checked on x64 and
arm with various -O values.
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 755bba9..7ff203b 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2887,7 +2887,6 @@
unsigned char *pms = ssl->handshake->premaster + pms_offset;
unsigned char fake_pms[48], peer_pms[48];
unsigned char mask;
- unsigned int uret;
size_t i;
if( ! pk_can_do( ssl_own_key( ssl ), POLARSSL_PK_RSA ) )
@@ -2951,10 +2950,7 @@
}
ssl->handshake->pmslen = 48;
- uret = (unsigned) ret;
- uret |= -uret; /* msb = ( ret != 0 ) */
- uret >>= 8 * sizeof( uret ) - 1; /* uret = ( ret != 0 ) */
- mask = (unsigned char)( -uret ) ; /* ret ? 0xff : 0x00 */
+ mask = (unsigned char)( - ( ret != 0 ) ); /* ret ? 0xff : 0x00 */
for( i = 0; i < ssl->handshake->pmslen; i++ )
pms[i] = ( mask & fake_pms[i] ) | ( (~mask) & peer_pms[i] );
