Code Generation/Example 3

The Original Code

Consider the following C function:

int *click(int *x, int dim) {
  int *res, i;
  for (i = dim-2, res = x+dim-1; i >= 0; i--)
    if (x[i] > *res) res = &x[i];
  return res;
}

Postfix Code

The Postfix code for the above function is as follows:

Postfix code

TEXT ALIGN GLOBL click, FUNC LABEL click ENTER 8 ;-- x@+8 dim@+12 res@-4 i@-8 ;; for init ;; i = dim-2 LOCAL 12 LDINT INT 2 SUB DUP32 LOCAL -8 STINT TRASH 4 ;; res = x + dim - 1 LOCAL 8 LDINT LOCAL 12 LDINT INT 4 MUL ADD INT 1 INT 4 MUL SUB DUP32 LOCAL -4 STINT TRASH 4 ;; for test ALIGN LABEL for LOCAL -8 LDINT INT 0 GE JZ forend ;; for block ;; if test LOCAL 8 LDINT ; x LOCAL -8 LDINT; i INT 4 MUL ADD ; x+i LDINT ; x[i] = *(x+i) LOCAL -4 LDINT ; res LDINT ; *res GT JZ ifend ;; if block LOCAL 8 LDINT ; x LOCAL -8 LDINT ; i INT 4 MUL ADD ; x+i = &x[i] DUP32 LOCAL -4 STINT ; res = &x[i] TRASH 4 ALIGN LABEL ifend ;; for increment ALIGN LABEL forincr LOCAL -8 LDINT ; i DUP32 INT 1 SUB LOCAL -8 STINT TRASH 4 ;; for jump to cycle JMP for ALIGN LABEL forend ;; return LOCAL -4 LDINT ; res STFVAL32 LEAVE RET

Compiling and Running

To compile the Postfix code directly, pf2asm can be used:

• pf2asm click.pf
• yasm -felf click.asm