Improve coding style

Co-authored-by: Tom Cosgrove <81633263+tom-cosgrove-arm@users.noreply.github.com>
Co-authored-by: Werner Lewis <werner.wmlewis@gmail.com>

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/library/bignum_core.c b/library/bignum_core.c
index d3d74ff..41be496 100644
--- a/library/bignum_core.c
+++ b/library/bignum_core.c
@@ -174,7 +174,10 @@
         memset( X, 0, X_limbs * ciL );
 
         for( size_t i = 0; i < input_length; i++ )
-            X[i / ciL] |= ((mbedtls_mpi_uint) input[i]) << ((i % ciL) << 3);
+        {
+            size_t offset = ( ( i % ciL ) << 3 );
+            X[i / ciL] |= ( (mbedtls_mpi_uint) input[i] ) << offset;
+        }
     }
 
     return( 0 );