pushc <const>

#define PUSHC 1 //1 is for the command value in the Opcode
#define IMMEDIATE(x) ((x) & 0x00FFFFFF)

**#define SIGN_EXTEND(i) ((i) & 0x00800000 ? (i) | 0xFF000000 : (i))**

unsigned int code[] = { (PUSHC << 24 | IMMEDIATE(2)),
                        (PUSHC << 24 | SIGN_EXTEND(-2)),
                         ...};

void exec(unsigned int IR){

      unsigned int opcode = (IR >> 24) & 0xff;
      unsigned int imm = (IR & 0xffffff);

     switch(opcode){
       case PUSHC: {
         stack[sp] = imm;
         sp = sp + 1;
         break;
}
}

    ...

    }
    }

const uint8_t opcode = (IR >> 24) & 0xff;
const uint32_t imm = (IR & 0xffffff);
switch(opcode)
{
  case PUSHC:
    stack[sp] = imm;
    break;
}