Performance difference between C and Matlab

Question

Friends,

I created two apparently identical encryption codes, one in C language and the other in Matlab, the code in Matlab has more functions, that is, it is more extensive and performs more functions than the code in C. To measure the execution time I am using the function tic and toc in Matlab, already in the C code I am using the function clocks (I am using Codeblocks as a programming IDE), but it seems that measuring a very different value and do not need in C code.

MatLab --> 0,049 segundos.
C --> 1 milisegundo.

Can anyone explain to me why that?

Follow the code in C:

main:

    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
    #include "ti_aes128.h"

    int main( void )
    {
        clock_t Ticks[2];
       Ticks[0] = clock();
      unsigned char state[] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
                                   0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff};

      unsigned char key1[]   = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                               0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};

      aes_enc_dec(state,key1,0);
      aes_enc_dec(state,key1,1);
       Ticks[1] = clock();
        double Tempo = (Ticks[1] - Ticks[0]) *1000 / CLOCKS_PER_SEC;
        printf("Tempo gasto: %g ms.", Tempo);
        getchar();
        return 0;
    }

ti_aes128:

// foreward sbox
const unsigned char sbox[256] =   {
//0     1    2      3     4    5     6     7      8    9     A      B    C     D     E     F
0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76, //0
0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0, //1
0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15, //2
0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75, //3
0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84, //4
0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf, //5
0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8, //6
0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2, //7
0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73, //8
0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb, //9
0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79, //A
0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08, //B
0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a, //C
0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e, //D
0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf, //E
0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16 }; //F

// inverse sbox
const unsigned char rsbox[256] =
{ 0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38, 0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb
, 0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87, 0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb
, 0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d, 0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e
, 0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2, 0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25
, 0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16, 0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92
, 0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda, 0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84
, 0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a, 0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06
, 0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02, 0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b
, 0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea, 0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73
, 0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85, 0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e
, 0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89, 0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b
, 0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20, 0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4
, 0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31, 0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f
, 0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d, 0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef
, 0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0, 0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61
, 0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26, 0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d };

// round constant
const unsigned char Rcon[10] = {
    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36};


// multiply by 2 in the galois field
unsigned char galois_mul2(unsigned char value)
{
  signed char temp;
  // cast to signed value
  temp = (signed char) value;
  // if MSB is 1, then this will signed extend and fill the temp variable with 1's
  temp = temp >> 7;
  // AND with the reduction variable
  temp = temp & 0x1b;
  // finally shift and reduce the value
  return ((value << 1)^temp);
}

// AES encryption and decryption function
// The code was optimized for memory (flash and ram)
// Combining both encryption and decryption resulted in a slower implementation
// but much smaller than the 2 functions separated
// This function only implements AES-128 encryption and decryption (AES-192 and
// AES-256 are not supported by this code)
void aes_enc_dec(unsigned char *state, unsigned char *key, unsigned char dir)
{
  unsigned char buf1, buf2, buf3, buf4, round, i;

  // In case of decryption
  if (dir) {
    // compute the last key of encryption before starting the decryption
    for (round = 0 ; round < 10; round++) {
      //key schedule
      key[0] = sbox[key[13]]^key[0]^Rcon[round];
      key[1] = sbox[key[14]]^key[1];
      key[2] = sbox[key[15]]^key[2];
      key[3] = sbox[key[12]]^key[3];
      for (i=4; i<16; i++) {
        key[i] = key[i] ^ key[i-4];
      }
    }

    //first Addroundkey
    for (i = 0; i <16; i++){
      state[i]=state[i] ^ key[i];
    }
  }

  // main loop
  for (round = 0; round < 10; round++){
    if (dir){
      //Inverse key schedule
      for (i=15; i>3; --i) {
    key[i] = key[i] ^ key[i-4];
      }
      key[0] = sbox[key[13]]^key[0]^Rcon[9-round];
      key[1] = sbox[key[14]]^key[1];
      key[2] = sbox[key[15]]^key[2];
      key[3] = sbox[key[12]]^key[3];
    } else {
      for (i = 0; i <16; i++){
        // with shiftrow i+5 mod 16
    state[i]=sbox[state[i] ^ key[i]];
      }
      //shift rows
      buf1 = state[1];
      state[1] = state[5];
      state[5] = state[9];
      state[9] = state[13];
      state[13] = buf1;

      buf1 = state[2];
      buf2 = state[6];
      state[2] = state[10];
      state[6] = state[14];
      state[10] = buf1;
      state[14] = buf2;

      buf1 = state[15];
      state[15] = state[11];
      state[11] = state[7];
      state[7] = state[3];
      state[3] = buf1;
    }
    //mixcol - inv mix
    if ((round > 0 && dir) || (round < 9 && !dir)) {
      for (i=0; i <4; i++){
        buf4 = (i << 2);
        if (dir){
          // precompute for decryption
          buf1 = galois_mul2(galois_mul2(state[buf4]^state[buf4+2]));
          buf2 = galois_mul2(galois_mul2(state[buf4+1]^state[buf4+3]));
          state[buf4] ^= buf1; state[buf4+1] ^= buf2; state[buf4+2] ^= buf1; state[buf4+3] ^= buf2;
        }
        // in all cases
        buf1 = state[buf4] ^ state[buf4+1] ^ state[buf4+2] ^ state[buf4+3];
        buf2 = state[buf4];
        buf3 = state[buf4]^state[buf4+1]; buf3=galois_mul2(buf3); state[buf4] = state[buf4] ^ buf3 ^ buf1;
        buf3 = state[buf4+1]^state[buf4+2]; buf3=galois_mul2(buf3); state[buf4+1] = state[buf4+1] ^ buf3 ^ buf1;
        buf3 = state[buf4+2]^state[buf4+3]; buf3=galois_mul2(buf3); state[buf4+2] = state[buf4+2] ^ buf3 ^ buf1;
        buf3 = state[buf4+3]^buf2;     buf3=galois_mul2(buf3); state[buf4+3] = state[buf4+3] ^ buf3 ^ buf1;
      }
    }

    if (dir) {
      //Inv shift rows
      // Row 1
      buf1 = state[13];
      state[13] = state[9];
      state[9] = state[5];
      state[5] = state[1];
      state[1] = buf1;
      //Row 2
      buf1 = state[10];
      buf2 = state[14];
      state[10] = state[2];
      state[14] = state[6];
      state[2] = buf1;
      state[6] = buf2;
      //Row 3
      buf1 = state[3];
      state[3] = state[7];
      state[7] = state[11];
      state[11] = state[15];
      state[15] = buf1;

      for (i = 0; i <16; i++){
        // with shiftrow i+5 mod 16
        state[i]=rsbox[state[i]] ^ key[i];
      }
    } else {
      //key schedule
      key[0] = sbox[key[13]]^key[0]^Rcon[round];
      key[1] = sbox[key[14]]^key[1];
      key[2] = sbox[key[15]]^key[2];
      key[3] = sbox[key[12]]^key[3];
      for (i=4; i<16; i++) {
        key[i] = key[i] ^ key[i-4];
      }
    }
  }
  if (!dir) {
  //last Addroundkey
    for (i = 0; i <16; i++){
      // with shiftrow i+5 mod 16
      state[i]=state[i] ^ key[i];
    } // enf for
  } // end if (!dir)
} // end function

Answer 1

In fact you don’t need a high resolution timer to solve your problem.

The secret is to perform your test over and over and then calculate the average time. See only:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "ti_aes128.h"

#define N (1000000L)

int main( void )
{
    time_t t0, t1, elapsed;
    double ms = 0;
    int i = 0;

    unsigned char state[] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77,
                            0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff};

    unsigned char key1[] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                            0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f};

    /* Recupera momento inicial */
    t0 = time(NULL);

    /* Executa o mesmo Teste N vezes... */
    for( i = 0; i < N; i++ )
    {
        /* Operacoes a serem testadas... */
        aes_enc_dec( state, key1, 0 );
        aes_enc_dec( state, key1, 1 );
    }

    /* Recupera momento final */
    t1 = time(NULL);

    /* Subtrai momento inicial do momento final */
    elapsed = t1 - t0;

    /* Calcula a media de tempo por execucao em milissegundos... */
    ms = ((double)(elapsed * 1000)) / N;

    printf("Media de tempo gasto por operacao: %g ms.\n", ms );

    return 0;
}