added check if startvalue == 1

Author: Christoph Zurnieden

mp_root_n.c

@@ -222,6 +222,9 @@ mp_err mp_root_n(const mp_int *a, int b, mp_int *c)
 
    /* 2^k, the start-value */
    if ((err = s_mp_fp_exp2(&t2, &t2)) != MP_OKAY)                             goto LBL_ERR;
+   if (mp_isone(&t2)) {
+      if ((err = mp_incr(&t2)) != MP_OKAY)                                   goto LBL_ERR;
+   }
    do {
 
       /* t1 = t2 */