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| Line 35: |
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| | ;-- while cycle: | | ;-- while cycle: |
| − | ALIGN
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| | LABEL "while" | | LABEL "while" |
| | LOCV -4 ; n | | LOCV -4 ; n |
| Line 62: |
Line 61: |
| | JMP "end3" ; jump to end of trenary operator | | JMP "end3" ; jump to end of trenary operator |
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| − | ALIGN
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| | LABEL "false3" | | LABEL "false3" |
| | LOCAL -8 ; &i | | LOCAL -8 ; &i |
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| − | ALIGN
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| | LABEL "end3" | | LABEL "end3" |
| | DUP32 ; trenary operator's value (duplicated because of assignment) | | DUP32 ; trenary operator's value (duplicated because of assignment) |
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| | JMP "while" ; restart while cycle | | JMP "while" ; restart while cycle |
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| − | ALIGN
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| | LABEL "endwhile" | | LABEL "endwhile" |
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Revision as of 23:26, 6 May 2020
The Original Code
Consider the following C function:
int main() {
int n = 45, i = 0, j = 1, *seg = &i;
while (n-- > 0) {
print(*seg = i + j);
seg = (seg == &i) ? &j : &i;
}
return 0;
}
Postfix Code
The Postfix code for the above function is as follows:
| [Expand] Postfix code
|
TEXT
ALIGN
GLOBAL "main",FUNC
LABEL "main"
ENTER 16 ; n@-4, i@-8, j@-12, seg@-16
;-- initialization:
INT 45
LOCA -4 ; n = 45
INT 0
LOCA -8 ; i = 0
INT 1
LOCA -12 ; j = 1
LOCAL -8 ; &i
LOCA -16 ; seg = &i
;-- while cycle:
LABEL "while"
LOCV -4 ; n
DUP32 ; n (because of n--)
INT 1
SUB ; n-1
LOCA -4 ; n = n-1
INT 0
GT ; n > 0 (n before decrement)
JZ "endwhile"
LOCV -8 ; i
LOCV -12 ; j
ADD ; i+j
DUP32 ; same value (for assignment)
LOCV -16 ; seg
STINT ; *seg = i+j
CALL "print" ; we assume that "print" does not return any value
TRASH 4 ; trash argument (int)
;-- compute trenary operator's value
LOCV -16 ; seg
LOCAL -8 ; &i
EQ ; seg == &i
JZ "false3" ; jump to "false" expression of trenary operator
LOCAL -12 ; &j
JMP "end3" ; jump to end of trenary operator
LABEL "false3"
LOCAL -8 ; &i
LABEL "end3"
DUP32 ; trenary operator's value (duplicated because of assignment)
LOCA -16 ; seg = (seg == &i) ? &j : &i
TRASH 4 ; trash assignment's value, since we used it as an instruction
JMP "while" ; restart while cycle
LABEL "endwhile"
;-- rest of function
INT 0
STFVAL32 ; return value is 0
LEAVE
RET
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