// Task - find the factorial of five

// Method - think at a high level. Write it out nice and
// cleanly in a familiar higher level language, and think
// step by step about how each part works.

// Notice when single stepping how jumps and global variable
// accesses use PC-relative addressing

// x = 5
// fact = 1
// while (x > 1)
// { fact *= x;
//   x -= 1; }

        .makeexe

        jump start

// x = 5
x:      .data 5         // initialising a global variable: this code
                        // is not "reentrant". After partially executing
                        // you can't just jump back to start if you
                        // want to start again. It would have to be
                        // reloaded from the executable file
// fact = 1
fact:   .data 1

// while (x > 1)

start:
loop:   load r1, [x]
        comp r1, 1              // if x<1 Nflag=1 else Nflag=0, and
                                // if x==1 Zflag=1 else Zflag=0
        jcond leq, endloop      // jump if Nflag || Zflag

// { fact *= x
        load r1, [fact]
        mul  r1, [x]
        store r1, [fact]

//   x -= 1
        dec  [x]

// end of while
        jump  loop

endloop:
        halt