Allow R and A to point to same mpi in mpi_div_mpi
(cherry picked from commit f02c5642d0f19281e7c30d849bf8cd94703a9bd5 and
from commit 50546921ac8250d1884c41fd9dc7a645007d4103)
diff --git a/library/bignum.c b/library/bignum.c
index acaba6a..079b58e 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1196,9 +1196,9 @@
     if( R != NULL )
     {
         mpi_shift_r( &X, k );
+        X.s = A->s;
         mpi_copy( R, &X );
 
-        R->s = A->s;
         if( mpi_cmp_int( R, 0 ) == 0 )
             R->s = 1;
     }
@@ -1400,19 +1400,6 @@
         return( POLARSSL_ERR_MPI_BAD_INPUT_DATA );
 
     /*
-     * Compensate for negative A (and correct at the end)
-     */
-    neg = ( A->s == -1 );
-
-    mpi_init( &Apos );
-    if( neg )
-    {
-        MPI_CHK( mpi_copy( &Apos, A ) );
-        Apos.s = 1;
-        A = &Apos;
-    }
-
-    /*
      * Init temps and window size
      */
     mpi_montg_init( &mm, N );
@@ -1433,6 +1420,19 @@
     MPI_CHK( mpi_grow( &T, j * 2 ) );
 
     /*
+     * Compensate for negative A (and correct at the end)
+     */
+    neg = ( A->s == -1 );
+
+    mpi_init( &Apos );
+    if( neg )
+    {
+        MPI_CHK( mpi_copy( &Apos, A ) );
+        Apos.s = 1;
+        A = &Apos;
+    }
+
+    /*
      * If 1st call, pre-compute R^2 mod N
      */
     if( _RR == NULL || _RR->p == NULL )