Improve comments in mpi_shrink
diff --git a/library/bignum.c b/library/bignum.c
index fdf571d..5ee34ae 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -157,9 +157,10 @@
if( nblimbs > MBEDTLS_MPI_MAX_LIMBS )
return( MBEDTLS_ERR_MPI_ALLOC_FAILED );
- /* Actually resize up in this case */
+ /* Actually resize up if there are currently fewer than nblimbs limbs. */
if( X->n <= nblimbs )
return( mbedtls_mpi_grow( X, nblimbs ) );
+ /* Now X->n > nblimbs >= 0. */
for( i = X->n - 1; i > 0; i-- )
if( X->p[i] != 0 )