IDIV -- Signed Divide

Opcode      Instruction        Clocks   Description

F6 /7       IDIV r/m8          19       Signed divide AX by r/m byte
                                        (AL=Quo, AH=Rem)
F7 /7       IDIV AX,r/m16      27       Signed divide DX:AX by EA word
                                        (AX=Quo, DX=Rem)
F7 /7       IDIV EAX,r/m32     43       Signed divide EDX:EAX by DWORD
                                        byte (EAX=Quo, EDX=Rem)

Operation

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

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

Description

IDIV performs a signed division. The dividend, quotient, and remainder are implicitly allocated to fixed registers. Only the divisor is given as an explicit r/m operand. The type of the divisor determines which registers to use as follows:

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

If the resulting quotient is too large to fit in the destination, or if the division is 0, an Interrupt 0 is generated. Nonintegral quotients are truncated toward 0. The remainder has the same sign as the dividend and the absolute value of the remainder is always less than the absolute value of the divisor.

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 or AX), 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 large to fit in the designated register (AL or AX), 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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