fix comments add/subtract

src/per_field/f_generic.tmpl.c

@@ -95,14 +95,14 @@ void gf_strong_reduce (gf a) {
     assert(word_is_zero(carry + scarry_0));
 }
 
-/** Add two gf elements */
+/** Subtract two gf elements d=a-b */
 void gf_sub (gf d, const gf a, const gf b) {
     gf_sub_RAW ( d, a, b );
     gf_bias( d, 2 );
     gf_weak_reduce ( d );
 }
 
-/** Subtract d = a-b */
+/** Add two field elements d = a+b */
 void gf_add (gf d, const gf a, const gf b) {
     gf_add_RAW ( d, a, b );
     gf_weak_reduce ( d );