3-264 Vol. 2A DIV—Unsigned Divide
INSTRUCTION SET REFERENCE, A-M
DIV—Unsigned Divide
Description
Divides unsigned the value in the AX, DX:AX, EDX:EAX, or RDX:RAX registers (divi-
dend) by the source operand (divisor) and stores the result in the AX (AH:AL),
DX:AX, EDX:EAX, or RDX:RAX 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). Division using 64-bit operand is available only in
64-bit mode.
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 unsigned value in RDX:RAX by the source operand and stores the
quotient in RAX, the remainder in RDX.
See the summary chart at the beginning of this section for encoding data and limits.
See Table 3-20.
Opcode Instruction 64-Bit
Mode
Compat/
Leg Mode
Description
F6 /6 DIV r/m8 Valid Valid Unsigned divide AX by r/m8, with
result stored in AL ← Quotient, AH ←
Remainder.
REX + F6 /6 DIV r/m8
*
Valid N.E. Unsigned divide AX by r/m8, with
result stored in AL ← Quotient, AH ←
Remainder.
F7 /6 DIV r/m16 Valid Valid Unsigned divide DX:AX by r/m16, with
result stored in AX ← Quotient, DX ←
Remainder.
F7 /6 DIV r/m32 Valid Valid Unsigned divide EDX:EAX by r/m32,
with result stored in EAX ← Quotient,
EDX ← Remainder.
REX.W + F7 /6 DIV r/m64 Valid N.E. Unsigned divide RDX:RAX by r/m64,
with result stored in RAX ← Quotient,
RDX ← Remainder.
NOTES:
* In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is
used: AH, BH, CH, DH.
