gistfile1.txt

#include <stdint.h>
#include <stdio.h>
#include <time.h>

int32_t interp(unsigned char *code, int initval)
{
  int pc = 0;
  int32_t val = initval;
  while(1) {
    switch(code[pc++]) {
    case 0:
      return val;
    case 1:
      val++;
      break;
    case 2:
      val--;
      break;
    case 3:
      val *= 2;
      break;
    case 4:
      val /= 2;
      break;
    case 5:
      val += 3;
      break;
    case 6:
      val = -val;
      break;
    case 7:
      val %= code[pc++];
      break;
    case 8:
    {
      int label = code[pc++];
      if (!val)
        pc = label;
      break;
    }
    case 9:
    {
      int cond = code[pc++];
      int label1 = code[pc++];
      int label2 = code[pc++];
      if (val < cond)
        pc = label1;
      else
        pc = label2;
      break;
    }
    }
  }
  return val;
}

int32_t interp_cgoto2(unsigned char* code, int initval)
{
  static void* dispatch_table[] = { &&do_halt, &&do_inc,  &&do_dec, &&do_mul2,
                                    &&do_div2, &&do_add7, &&do_neg, &&do_mod, &&do_jmpz, &&do_jmplt };
  int pc = 0;
  int32_t val = initval;

  goto *dispatch_table[code[pc++]];
  while (1) {
  do_halt: // 0
    return val;
  do_inc: // 1
    val++;
    goto *dispatch_table[code[pc++]];
    continue;
  do_dec: // 2
    val--;
    goto *dispatch_table[code[pc++]];
    continue;
  do_mul2: // 3
    val *= 2;
    goto *dispatch_table[code[pc++]];
    continue;
  do_div2: // 4
    val /= 2;
    goto *dispatch_table[code[pc++]];
    continue;
  do_add7: // 5
    val += 3;
    goto *dispatch_table[code[pc++]];
    continue;
  do_neg: // 6
    val = -val;
    goto *dispatch_table[code[pc++]];
    continue;
  do_mod: // 7
    val %= code[pc++];
    goto *dispatch_table[code[pc++]];
    continue;
  do_jmpz: // 8
  {
    int label = code[pc++];
    if (!val)
      pc = label;
    goto *dispatch_table[code[pc++]];
    continue;
  }
  do_jmplt: // 9
  {
    int cond = code[pc++];
    int label1 = code[pc++];
    int label2 = code[pc++];
    if (val < cond)
      pc = label1;
    else
      pc = label2;
    goto *dispatch_table[code[pc++]];
    continue;
  }
  }
}

int main(int argc, char *argv[]) {
   unsigned char code[] = {
     1, // inc
   // start:
     1, // inc
     9, 0, 6, 0, // jmplt(0, end, start)
   // end:
     0, // hlt
   };

   // printf("Calc finish: %x\n", interp(code, 0));
   // printf("Calc finish: %x\n", interp_cgoto2(code, 0));

   clock_t start, finish;
   double cpu_time_used;

   start = clock();
   for (int i = 0; i < 4; i++)
     printf("%x\n", interp_cgoto2(code, 0));
   finish = clock();
   cpu_time_used = ((double) (finish - start)) / CLOCKS_PER_SEC;
   printf("CGOTO took: %f\n", cpu_time_used);

   start = clock();
   for (int i = 0; i < 4; i++)
     printf("%x\n", interp(code, 0));
   finish = clock();
   cpu_time_used = ((double) (finish - start)) / CLOCKS_PER_SEC;
   printf("SWITCH took: %f\n", cpu_time_used);

   return 0;
}