Merge branch 'pr_1480' into development-proposed
diff --git a/ChangeLog b/ChangeLog
index 8c0dbb1..2af6cf2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -63,6 +63,8 @@
Alex Hixon.
* Allow configuring the shared library extension by setting the DLEXT
environment variable when using the project makefiles.
+ * Optimize unnecessary zeroing in mbedtls_mpi_copy. Based on a contribution
+ by Alexey Skalozub in #405.
= mbed TLS 2.8.0 branch released 2018-03-16
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 3bf02a7..31383b1 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -204,6 +204,8 @@
/**
* \brief Enlarge to the specified number of limbs
*
+ * This function does nothing if the MPI is already large enough.
+ *
* \param X MPI to grow
* \param nblimbs The target number of limbs
*
@@ -215,19 +217,23 @@
/**
* \brief Resize down, keeping at least the specified number of limbs
*
+ * If \c X is smaller than \c nblimbs, it is resized up
+ * instead.
+ *
* \param X MPI to shrink
* \param nblimbs The minimum number of limbs to keep
*
* \return 0 if successful,
* MBEDTLS_ERR_MPI_ALLOC_FAILED if memory allocation failed
+ * (this can only happen when resizing up).
*/
int mbedtls_mpi_shrink( mbedtls_mpi *X, size_t nblimbs );
/**
* \brief Copy the contents of Y into X
*
- * \param X Destination MPI
- * \param Y Source MPI
+ * \param X Destination MPI. It is enlarged if necessary.
+ * \param Y Source MPI.
*
* \return 0 if successful,
* MBEDTLS_ERR_MPI_ALLOC_FAILED if memory allocation failed
diff --git a/library/bignum.c b/library/bignum.c
index ff72d30..47bf1ef 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: