Code Generation/Duplication of Floating Point Numbers on the Stack

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

The C equivalent would be (roughly):

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

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

Postfix code

;;-- generation of the "_main" function
TEXT
ALIGN
GLOBAL _main, FUNC
LABEL _main
ENTER 16   ; d@-8 and e@-16

;;-- put double literal in RODATA
RODATA
ALIGN
LABEL _L123
SDOUBLE 3.3e-2

;;-- load literal onto stack
TEXT
ADDR _L123
LDDOUBLE

;;-- to perform the first assignment (to "e"), duplicate the value on the stack
DUP64

LOCAL -16  ; write value to "e"
STDOUBLE

;;-- to perform the second assignment (to "d"), duplicate the value on the stack
DUP64

LOCAL -8  ; write value to "d"
STDOUBLE

;;-- the assignments are an instruction: trash the value left on the stack
TRASH 8

;;-- now to perform the add operation
LOCAL -8
LDDOUBLE   ; load "d"
LOCAL -16
LDDOUBLE ; load "e"

DADD   ; leaves result on the stack

EXTERN printd
CALL printd

TRASH 8  ; argument value no longer needed

INT 0
STFVAL32
LEAVE
RET

Compiling and Running

Assuming that the code above is in file dbl.pf, the following commands (pf2asm) would compile and run the program:

pf2asm dbl.pf
yasm -felf32 dbl.asm
ld -m elf_i386 -o dbl dbl.o -lrts
./dbl

Code Generation/Duplication of Floating Point Numbers on the Stack

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Compiling and Running