XTEA, the eXtended Tiny Encryption Algorithm

XTEA.cpp

#include <stdint.h>

// key schedule constant
#define delta 0x9e3779b9

void encrypt (uint32_t n, uint32_t* v, uint32_t* k) {
    // setup
    uint32_t v0 = v[0];
    uint32_t v1 = v[1];
    uint32_t sum = 0;
    uint32_t i;
    
    // cache key
    uint32_t kk[4];
    kk[0] = k[0];
    kk[1] = k[1];
    kk[2] = k[2];
    kk[3] = k[3];
    
    // run cycles
    for (i = 0; i < n; i++) {
        v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + kk[sum & 3]);
        sum += delta;
        v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + kk[(sum >> 11) & 3]);
    }
    
    // store result
    v[0] = v0;
    v[1] = v1;
}
 
void decrypt (uint32_t n, uint32_t* v, uint32_t* k) {
    // setup
    uint32_t v0 = v[0];
    uint32_t v1 = v[1];
    uint32_t sum = delta * n;
    uint32_t i;
    
    // cache key
    uint32_t kk[4];
    kk[0] = k[0];
    kk[1] = k[1];
    kk[2] = k[2];
    kk[3] = k[3];
    
    // run cycles
    for (i = 0; i < n; i++) {
        v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + kk[(sum >> 11) & 3]);
        sum -= delta;
        v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + kk[sum & 3]);
    }
    
    // store result
    v[0] = v0;
    v[1] = v1;
}