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Basic Arithmetic

ADD​

SUB​

INC​

DEC​

MUL​

Multiplies eax by a value and stores the result 64-bit value across edx:eax:

mul value

mul 0x10

DIV​

Divides one number by another

DIV arg

Some forms:

  • arg of size 8 bits:
al <- ax / arg; quotient
ah <- ax % arg; remainder
  • arg of size 16 bits:
ax <- dx:ax / arg
dx <- dx:ax % arg
  • arg of size 32 bits:
eax <- edx:eax / arg
edx <- edx:eax % arg

Examples:

  • div ch: divides ch and stores the division result inside al. The remainder is stored inside ah.
  • div esi: divides edx:eax by esi. Stores the quotient inside eax. Stores the remainder inside edx.
  • div di: divides dx:ax by di. Stores the quotient inside eax. Stores the remainder inside edx.

edx:eax is the extension of edx:eax so:

mv edx, '20' ; edx:eax is now 0000002000000000
mv ebx, '3A' 

div ebx      ; divide edx:eax by ebx ==> eax= 8D3DCB0, edx=30 (remainder)

div bx       
; divide ax:dx by bx ==> 
bx == 3A
dx:ax== 30CB08

ax == D75C (quotient)
dx == 0 (remainder)