commit 4e4be7cf623803865d4259f6c3a11414b6565221
author Gilles Peskine <Gilles.Peskine@arm.com> Wed Mar 21 16:29:03 2018 +0100
committer Gilles Peskine <Gilles.Peskine@arm.com> Wed Mar 21 16:29:03 2018 +0100
tree 18566e0614a26727c0506ccb9ea419cc5923314c
parent 70ad8397259f96f53104929b0c416f6617280b69

Optimize unnecessary zeorizing in mbedtls_mpi_copy

Based on a contribution by Alexey Skalozub
(https://github.com/ARMmbed/mbedtls/pull/405).

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index d27c130..e57e6af 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -184,7 +184,7 @@
  */
 int mbedtls_mpi_copy( mbedtls_mpi *X, const mbedtls_mpi *Y )
 {
-    int ret;
+    int ret = 0;
     size_t i;
 
     if( X == Y )
@@ -203,9 +203,15 @@
 
     X->s = Y->s;
 
-    MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, i ) );
+    if( X->n < i )
+    {
+        MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, i ) );
+    }
+    else
+    {
+        memset( X->p + i, 0, ( X->n - i ) * ciL );
+    }
 
-    memset( X->p, 0, X->n * ciL );
     memcpy( X->p, Y->p, i * ciL );
 
 cleanup: