IDIV

Signed Divide

stableVMJITAOTinstruction

Encodings

Opcode	Instruction	Op/En	64-bit	Compat/Legacy	Description
`F6 /7`	`IDIV r/m8`	M	Valid	Valid	Signed divide AX by r/m8, with result stored in: AL := Quotient, AH := Remainder.
`F7 /7`	`IDIV r/m16`	M	Valid	Valid	Signed divide DX:AX by r/m16, with result stored in AX := Quotient, DX := Remainder.
`F7 /7`	`IDIV r/m32`	M	Valid	Valid	Signed divide EDX:EAX by r/m32, with result stored in EAX := Quotient, EDX := Remainder.
`REX.W + F7 /7`	`IDIV r/m64`	M	Valid	Not encodable	Signed divide RDX:RAX by r/m64, with result stored in RAX := Quotient, RDX := Remainder.

Operand encoding

Each mode is a value of the Op/En column above. It says which field of the encoded instruction carries each operand, in the order they are written, and whether the instruction reads it, writes it or both.

M

modrm.rm lecturaModRM byte, r/m field (bits 2-0); with the SIB byte and the displacement when the mod field asks for them

Measured cost

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Flags named

CF Carry
PF Parity
AF Auxiliary carry
ZF Zero
SF Sign
OF Overflow

Description

Divides the (signed) value in the AX, DX:AX, or EDX:EAX (dividend) by the source operand (divisor) and stores the result in the AX (AH:AL), DX:AX, or EDX:EAX registers. The source operand can be a general-purpose register or a memory location. The action of this instruction depends on the operand size (dividend/divisor).

Non-integral results are truncated (chopped) towards 0. The remainder is always less than the divisor in magnitude. Overflow is indicated with the #DE (divide error) exception rather than with the CF flag.

In 64-bit mode, the instruction's default operation size is 32 bits. Use of the REX.R prefix permits access to additional registers (R8-R15). Use of the REX.W prefix promotes operation to 64 bits. In 64-bit mode when REX.W is applied, the instruction divides the signed value in RDX:RAX by the source operand. RAX contains a 64-bit quotient; RDX contains a 64-bit remainder.

See the summary chart at the beginning of this section for encoding data and limits. See Table 3-53.

IDIV Results

Operand Size	Dividend	Divisor	Quotient	Remainder	Quotient Range
e AX		r/m8 AL		AH	-128 to +127

Operation

IF SRC = 0

    THEN #DE; (* Divide error *)
FI;

IF OperandSize = 8 (* Word/byte operation *)

    THEN
          temp := AX / SRC; (* Signed division *)
          IF (temp > 7FH) or (temp < 80H)
          (* If a positive result is greater than 7FH or a negative result is less than 80H *)
                THEN #DE; (* Divide error *)
                ELSE
                       AL := temp;
                       AH := AX SignedModulus SRC;
          FI;

   ELSE IF OperandSize = 16 (* Doubleword/word operation *)

          THEN
                temp := DX:AX / SRC; (* Signed division *)
                IF (temp > 7FFFH) or (temp < 8000H)
                (* If a positive result is greater than 7FFFH
                or a negative result is less than 8000H *)
                       THEN
                             #DE; (* Divide error *)
                       ELSE
                             AX := temp;
                             DX := DX:AX SignedModulus SRC;
                FI;

          FI;
    ELSE IF OperandSize = 32 (* Quadword/doubleword operation *)

                temp := EDX:EAX / SRC; (* Signed division *)
                IF (temp > 7FFFFFFFH) or (temp < 80000000H)
                (* If a positive result is greater than 7FFFFFFFH
                or a negative result is less than 80000000H *)

                       THEN
                             #DE; (* Divide error *)

                       ELSE
                             EAX := temp;
                             EDX := EDXE:AX SignedModulus SRC;

                FI;
          FI;
    ELSE IF OperandSize = 64 (* Doublequadword/quadword operation *)

                temp := RDX:RAX / SRC; (* Signed division *)
                IF (temp > 7FFFFFFFFFFFFFFFH) or (temp < 8000000000000000H)
                (* If a positive result is greater than 7FFFFFFFFFFFFFFFH
                or a negative result is less than 8000000000000000H *)

                       THEN
                             #DE; (* Divide error *)

                       ELSE
                             RAX := temp;
                             RDX := RDE:RAX SignedModulus SRC;

                FI;
          FI;
FI;

Flags affected

The CF, OF, SF, ZF, AF, and PF flags are undefined.

Exceptions

Protected mode

`#DE`	If the source operand (divisor) is 0. The signed result (quotient) is too large for the destination.
`#GP(0)`	If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit. If the DS, ES, FS, or GS register is used to access memory and it contains a NULL segment selector.
`#SS(0)`	If a memory operand effective address is outside the SS segment limit. #PF(fault-code) If a page fault occurs.
`#AC(0)`	If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
`#UD`	If the LOCK prefix is used.

Real address mode

`#DE`	If the source operand (divisor) is 0.
`#GP`	The signed result (quotient) is too large for the destination.
`#SS`	If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
`#UD`	If a memory operand effective address is outside the SS segment limit. If the LOCK prefix is used.

Virtual-8086 mode

`#DE`	If the source operand (divisor) is 0.
`#GP(0)`	The signed result (quotient) is too large for the destination.
`#SS(0)`	If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
`#PF(fault-code)`	If a memory operand effective address is outside the SS segment limit.
`#AC(0)`	If a page fault occurs.
`#UD`	If alignment checking is enabled and an unaligned memory reference is made. If the LOCK prefix is used.

Compatibility mode

Same exceptions as in protected mode.

64-bit mode

`#SS(0)`	If a memory address referencing the SS segment is in a non-canonical form.
`#GP(0)`	If the memory address is in a non-canonical form.
`#DE`	If the source operand (divisor) is 0 If the quotient is too large for the designated register. #PF(fault-code) If a page fault occurs.
`#AC(0)`	If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.
`#UD`	If the LOCK prefix is used.

IDIV

Encodings

Operand encoding

M

Measured cost

Flags named

Description#

Operation#

Flags affected#

Exceptions

Sources

Description

Operation

Flags affected