(→Compiling and Running) |
(→Postfix Code) |
||
Line 27: | Line 27: | ||
ENTER 12 | ENTER 12 | ||
INT 1 | INT 1 | ||
− | + | LOCAL -4 | |
+ | STORE | ||
INT 0 | INT 0 | ||
− | + | LOCAL -8 | |
− | + | STORE | |
− | + | LOCAL +8 | |
+ | LOAD | ||
+ | LOCAL -12 | ||
+ | STORE | ||
ALIGN | ALIGN | ||
LABEL while | LABEL while | ||
− | + | LOCAL +12 | |
− | + | LOAD | |
+ | LOCAL -8 | ||
+ | LOAD | ||
SHTRU | SHTRU | ||
INT 0 | INT 0 | ||
Line 42: | Line 48: | ||
JZ while_end | JZ while_end | ||
− | + | LOCAL +12 | |
− | + | LOAD | |
+ | LOCAL -8 | ||
+ | LOAD | ||
SHTRU | SHTRU | ||
INT 1 | INT 1 | ||
Line 51: | Line 59: | ||
JZ if_end | JZ if_end | ||
− | + | LOCAL -4 | |
− | + | LOAD | |
+ | LOCAL -12 | ||
+ | LOAD | ||
MUL | MUL | ||
− | + | LOCAL +16 | |
+ | LOAD | ||
MOD | MOD | ||
DUP | DUP | ||
− | + | LOCAL -4 | |
+ | STORE | ||
TRASH 4 | TRASH 4 | ||
Line 63: | Line 75: | ||
LABEL if_end | LABEL if_end | ||
− | + | LOCAL -12 | |
− | + | LOAD | |
+ | LOCAL -12 | ||
+ | LOAD | ||
MUL | MUL | ||
− | + | LOCAL +16 | |
+ | LOAD | ||
MOD | MOD | ||
DUP | DUP | ||
− | + | LOCAL -12 | |
+ | STORE | ||
TRASH 4 | TRASH 4 | ||
− | + | LOCAL -8 | |
+ | LOAD | ||
DUP | DUP | ||
INT 1 | INT 1 | ||
ADD | ADD | ||
− | + | LOCAL -8 | |
+ | STORE | ||
TRASH 4 | TRASH 4 | ||
Line 82: | Line 100: | ||
LABEL while_end | LABEL while_end | ||
− | + | LOCAL -4 | |
+ | LOAD | ||
POP | POP | ||
LEAVE | LEAVE |
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 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