IDIV

Signed Divide

참고 사항

Instruction Operand Encoding

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 magni-tude. 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 addi-tional 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 3-50.

Table 3-50. IDIV Results

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.

Protected Mode Exceptions

#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 Exceptions

#DE

• If the source operand (divisor) is 0.

• The signed result (quotient) is too large for the destination.

#GP

• If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.

#SS

• If a memory operand effective address is outside the SS segment limit.

#UD

• If the LOCK prefix is used.

Virtual-8086 Mode Exceptions

#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.

#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.

#UD

• If the LOCK prefix is used.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

#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.

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