Added comment description of cmov_int16

ref/verify.c

@@ -56,7 +56,17 @@ void cmov(uint8_t *r, const uint8_t *x, size_t len, uint8_t b)
     r[i] ^= b & (r[i] ^ x[i]);
 }
 
-
+/*************************************************
+* Name:        cmov_int16
+*
+* Description: Copy input v to *r if b is 1, don't modify *r if b is 0. 
+*              Requires b to be in {0,1};
+*              Runs in constant time.
+*
+* Arguments:   int16_t *r:       pointer to output int16_t
+*              int16_t v:        input int16_t 
+*              uint8_t b:        Condition bit; has to be in {0,1}
+**************************************************/
 void cmov_int16(int16_t *r, int16_t v, uint16_t b)
 {
   b = -b;