Added ecp_sub() as a variant of ecp_add()
diff --git a/include/polarssl/ecp.h b/include/polarssl/ecp.h
index cea403a..f3e636e 100644
--- a/include/polarssl/ecp.h
+++ b/include/polarssl/ecp.h
@@ -201,6 +201,20 @@
const ecp_point *P, const ecp_point *Q );
/**
+ * \brief Subtraction: R = P - Q
+ *
+ * \param grp ECP group
+ * \param R Destination point
+ * \param P Left-hand point
+ * \param Q Right-hand point
+ *
+ * \return 0 if successful,
+ * POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
+ */
+int ecp_sub( const ecp_group *grp, ecp_point *R,
+ const ecp_point *P, const ecp_point *Q );
+
+/**
* \brief Multiplication by an integer: R = m * P
*
* \param grp ECP group