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| == The Original Code ==
| | #REDIRECT [[ist:Code Generation/Exercise 6]] |
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| Consider the following C function:
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| <c>
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| int powmod(int base, int exp, int modulus) {
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| int accum = 1, i = 0, basepow2 = base;
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| while ((exp >> i) > 0) {
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| if (((exp >> i) & 1) == 1)
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| accum = (accum * basepow2) % modulus;
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| basepow2 = (basepow2 * basepow2) % modulus;
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| i++;
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| }
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| return accum;
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| }
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| </c>
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| == Postfix Code ==
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| The Postfix code for the above function is as follows:
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| <asm>
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| TEXT
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| ALIGN
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| GLOBL powmod, FUNC
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| LABEL powmod
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| ENTER 12
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| INT 1
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| LOCA -4
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| INT 0
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| LOCA -8
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| LOCV +8
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| LOCA -12
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| ALIGN
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| LABEL while
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| LOCV +12
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| LOCV -8
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| SHTRU
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| INT 0
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| GT
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| JZ while_end
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| LOCV +12
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| LOCV -8
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| SHTRU
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| INT 1
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| AND
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| INT 1
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| EQ
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| JZ if_end
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| LOCV -4
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| LOCV -12
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| MUL
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| LOCV +16
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| MOD
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| DUP
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| LOCA -4
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| TRASH 4
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| ALIGN
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| LABEL if_end
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| LOCV -12
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| LOCV -12
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| MUL
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| LOCV +16
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| MOD
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| DUP
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| LOCA -12
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| TRASH 4
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| LOCV -8
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| DUP
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| INT 1
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| ADD
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| LOCA -8
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| TRASH 4
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| JMP while
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| LABEL while_end
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| LOCV -4
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| POP
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| LEAVE
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| RET
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| </asm>
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| == Compiling and Running ==
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| To compile the Postfix code directly, [[pf2asm]] can be used:
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| * pf2asm gcd.pf
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| * yasm -felf gcd.asm
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| [[category:Compilers]]
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| [[category:Teaching]]
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