UMBC CMSC 211

Operations for Multiple Precision

There are two instructions for multi-byte operations:

adc	dest, source		;dest = dest + source + CarryFlag
sbc	dest, source		;dest = dest - source - CarryFlag

Now we can do something like:

carry   carry   carry   carry   carry
   A4      A3      A2      A1      A0
+  B4      B3      B2      B1      B0
-----   -----   -----   -----   -----
   C4      C3      C2      C1      C0

Now we can have the following code:

;  Multiple precision addition
        mov   eax, A0
        add   eax, B0
        mov   C0, eax           ; Does not affect the carry flag!
        mov   eax, A1           ; Does not affect the carry flag!
        adc   eax, B1
        mov   C1, eax           ; Does not affect the carry flag!
        mov   eax, A2           ; Does not affect the carry flag!
        adc   eax, B2
        mov   C2, eax           ; Does not affect the carry flag!
        mov   eax, A3           ; Does not affect the carry flag!
        adc   eax, B3
        mov   C3, eax           ; Does not affect the carry flag!
        mov   eax, A4           ; Does not affect the carry flag!
        adc   eax, B4
        mov   C4, eax           ; Does not affect the carry flag!

Check this out, 4 x 32 = 160 bit value!!!! That ought to be big enough for your starting monthly salary!

There are two other instructions that do not affect the carry flag, inc and dec.

MPPUTDEC.ASM

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