Intel and compatable CPU's Programming Information
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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)
temp := dividend / divisor; IF temp does not fit in quotient THEN Interrupt 0; ELSE quotient := temp; remainder := dividend MOD (r/m); FI;
NotesDivisions 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"
DescriptionIDIV 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:EAXIf 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 AffectedOF, SF, ZF, AR, PF, CF are undefined.
Protected Mode ExceptionsInterrupt 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 ExceptionsInterrupt 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 ExceptionsSame exceptions as in Real Address Mode; #PF(fault-code) for a page fault