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https://github.com/vxunderground/MalwareSourceCode
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43 lines
1.1 KiB
NASM
43 lines
1.1 KiB
NASM
SUBR PROC FAR
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SPACE
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; -------------------------------------------------------------------
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; ADD BCD NUMBERS
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; THIS ROUTINE ADDS TWO BCD NUMBERS OF EQUAL LENGTH
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; ASSUMPTIONS:
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; CX CONTAINS THE LENGTH OF THE FIELDS BEING ADDED
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; SI POINTS TO THE LEFTMOST BYTE OF THE BCD DATA
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; DI POINTS TO THE SECOND OPPERAND WHICH IS OVERLAID BY RESULT
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; AX DESTROYED BY THIS ROUTINE
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;
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BCDADD LABEL FAR
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CLC ;CLEAR CARY FLAG
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BCD1 LABEL NEAR
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MOV AL,[SI] ;GET A DATA BYTE
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ADC AL,[DI] ;ADD A BYTE
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DAA ;ADJUST RESULT
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MOV [DI],AL ;STORE ANSWER
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INC SI ;BUMP POINTER
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INC DI ;BUMP POINTER
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DEC CX ;DECREMENT AND TEST
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JNZ BCD1 ;LOOP TILL DONE
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RET ;BACK TO CALLER
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SPACE 2
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; ADD ASCII NUMBERS
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; LINKAGE IS SAME AS ABOVE
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;
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ASCADD LABEL FAR
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CLC ;CLEAR CARRY FLAG
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ASC1 LABEL NEAR
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MOV AL,[SI] ;GET A BYTE
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ADC AL,[DI] ;ADD DATA
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AAA ;ADJUST RESULT
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MOV [DI],AL ;STORE ANSWER
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INC SI ;BUMP POINTER
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INC DI ;BUMP POINTER
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DEC CX ;LOOP CONTROL
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JNZ ASC1 ;LOOP FOR MORE
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RET
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;
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; -------------------------------------------------------------
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SUBR ENDP
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