Consider the following C function:
<c> int powmod(int base, int exp, int modulus) {
int accum = 1, i = 0, basepow2 = base;
while ((exp >> i) > 0) {
if (((exp >> i) & 1) == 1)
accum = (accum * basepow2) % modulus;
basepow2 = (basepow2 * basepow2) % modulus;
i++;
}
return accum;
} </c>
The Postfix code for the above function is as follows:
<asm> TEXT ALIGN GLOBL powmod, FUNC LABEL powmod ENTER 12 INT 1 LOCA -4 INT 0 LOCA -8 LOCV +8 LOCA -12
ALIGN LABEL while LOCV +12 LOCV -8 SHTRU INT 0 GT JZ while_end
LOCV +12 LOCV -8 SHTRU INT 1 AND INT 1 EQ JZ if_end
LOCV -4 LOCV -12 MUL LOCV +16 MOD DUP LOCA -4 TRASH 4
ALIGN LABEL if_end
LOCV -12 LOCV -12 MUL LOCV +16 MOD DUP LOCA -12 TRASH 4
LOCV -8 DUP INT 1 ADD LOCA -8 TRASH 4
JMP while LABEL while_end
LOCV -4 POP LEAVE RET </asm>
To compile the Postfix code directly, pf2asm can be used: