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:
| Postfix code |
|---|
|
<asm> TEXT ALIGN GLOBL powmod, FUNC LABEL powmod ENTER 12 INT 1 LOCAL -4 STORE INT 0 LOCAL -8 STORE LOCAL +8 LOAD LOCAL -12 STORE ALIGN LABEL while LOCAL +12 LOAD LOCAL -8 LOAD SHTRU INT 0 GT JZ while_end LOCAL +12 LOAD LOCAL -8 LOAD SHTRU INT 1 AND INT 1 EQ JZ if_end LOCAL -4 LOAD LOCAL -12 LOAD MUL LOCAL +16 LOAD MOD DUP LOCAL -4 STORE TRASH 4 ALIGN LABEL if_end LOCAL -12 LOAD LOCAL -12 LOAD MUL LOCAL +16 LOAD MOD DUP LOCAL -12 STORE TRASH 4 LOCAL -8 LOAD DUP INT 1 ADD LOCAL -8 STORE TRASH 4 JMP while LABEL while_end LOCAL -4 LOAD POP LEAVE RET </asm> |
To compile the Postfix code directly, pf2asm can be used:
pf2asm powmod.pf yasm -felf powmod.asm