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80386 Programmer's Reference Manual -- Opcode DIV

DIV -- Unsigned Divide

Opcode	Instruction	Clocks	Description	Example
F6 /6	divb r/m8,al	14/17	Unsigned divide AX by r/m byte (AL=Quo, AH=Rem)	`divb %dl,%al divb (%ebx,1),%al divb m8(%ebx,1),%al divb m8(%ebx,%ebp,1),%al`
F7 /6	divw r/m16,ax	22/25	Unsigned divide DX:AX by r/m word (AX=Quo, DX=Rem)	`divw %cx,%ax divw (%ebx,1),%ax divw (%ebx,2),%ax divw (%ebx,%ebp,1),%ax`
F7 /6	divl r/m32,eax	38/41	Unsigned divide EDX:EAX by r/m dword (EAX=Quo, EDX=Rem)	`divl %ecx,%eax divl (%ebx,2),%eax divl (%ebx,4),%eax divl (%ebx,%ebp,1),%eax`

Operation




temp := dividend / divisor;
IF temp does not fit in quotient
THEN Interrupt 0;
ELSE
   quotient := temp;
   remainder := dividend MOD (r/m);
FI;

Note
Divisions are unsigned. The divisor is given by the r/m operand. The dividend, quotient, and remainder use implicit registers. Refer to the table under "Description"

Description

DIV performs an unsigned division. The dividend is implicit; only the divisor is given as an operand. The remainder is always less than the divisor. The type of the divisor determines which registers to use as follows:





    Size    Dividend     Divisor   Quotient   Remainder
    byte    AX           r/m8       AL          AH
    word    DX:AX        r/m16      AX          DX
    dword   EDX:EAX      r/m32      EAX         EDX

Flags Affected

OF, SF, ZF, AR, PF, CF are undefined.

Protected Mode Exceptions

Interrupt 0 if the quotient is too large to fit in the designated register (AL, AX, or EAX), or if the divisor is 0; #GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault

Real Address Mode Exceptions

Interrupt 0 if the quotient is too big to fit in the designated register (AL, AX, or EAX), or if the divisor is 0; Interrupt 13 if any part of the operand would lie outside of the effective address space from 0 to 0FFFFH

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault

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