Revision as of 17:20, 13 May 2013

NOTE: this code was necessary before the addition of the DDUP instruction to the Postfix mnemonics set.

The following pure-Postfix program illustrates duplication of double-precision floating point numbers on the stack.

The C equivalent would be (roughly):

<c> int main() {

 extern void printd(double);
 double d, e;
 d = e = 3.3e-2;
 printd(d + e);
 return 0;

} </c>

Note that this program's code does not necessarily correspond to any particular code generator output.

<asm>

-- generation of the "_main" function

TEXT ALIGN GLOBL _main, FUNC LABEL _main ENTER 16  ; d@-8 and e@-16

-- put double literal in RODATA

RODATA ALIGN LABEL _L123 DOUBLE 3.3e-2

-- load literal onto stack

TEXT ADDR _L123 DLOAD

-- to perform the first assignment (to "e"), duplicate the value on the stack

DDUP

LOCAL -16  ; write value to "e" DSTORE

-- to perform the second assignment (to "d"), duplicate the value on the stack

DDUP

LOCAL -8  ; write value to "d" DSTORE

-- the assignments are an instruction

trash the value left on the stack

TRASH 8

-- now to perform the add operation

LOCAL -8 DLOAD  ; load "d" LOCAL -16 DLOAD ; load "e"

DADD  ; leaves result on the stack

EXTERN printd CALL printd

TRASH 8  ; argument value no longer needed

INT 0 POP LEAVE RET </asm>

Compiling and Running

Assuming that the code above is in file dbl.pf, the following commands would compile and run the program:

• pf2asm dbl.pf
• yasm -felf dbl.asm
• ld -o dbl dbl.o -lrts
• ./dbl