#include <stdint.h>
 
 typedef uint32_t word;
 
 #define CONST 0x9E3779B9
 #define ROUNDS 16
 
 #define ROTL(X, R) (((X) << ((R) & 31)) | ((X) >> (32 - ((R) & 31))))
 #define ROTR(X, R) (((X) >> ((R) & 31)) | ((X) << (32 - ((R) & 31))))
 
 void encrypt(word * x, const word * k)
 {
   unsigned int i;
   word rk0 = k[0];
   word rk1 = k[1];
 
   for (i = 0; i < ROUNDS; i++)
   {
     rk0 += CONST;
     rk1 -= CONST;
 
     x[0] ^= rk0;
     x[0] += x[1];
     x[0] = ROTL(x[0], x[1]);
 
     x[1] = ROTR(x[1], x[0]);
     x[1] -= x[0];
     x[1] ^= rk1;
   }
 
   rk0 = x[0]; x[0] = x[1]; x[1] = rk0;
 }
 
 void decrypt(word * x, const word * k)
 {
   word dk[2] =
   {
     k[1] - CONST * (ROUNDS + 1),
     k[0] + CONST * (ROUNDS + 1)
   };
 
   encrypt(x, dk);
 }