Signed divide AX (where AH
must contain sign-extension of AL) by r/m
byte. (Results: AL=Quotient, AH=Remainder)
F7 /7
IDIV r/m16
Signed divide DX:AX (where
DX must contain sign-extension of AX) by r/m
word. (Results: AX=Quotient, DX=Remainder)
F7 /7
IDIV r/m32
Signed divide EDX:EAX (where
EDX must contain sign-extension of EAX) by r/m
doubleword. (Results: EAX=Quotient, EDX=Remainder)
Description
Divides (signed) the value in the AL, AX, or EAX register by the source
operand and stores the result in the AX, 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, as shown in
the following table:
Operand Size
Dividend
Divisor
Quotient
Remainder
Quotient Range
Word/byte
AX
r/m8
AL
AH
-128 to +127
Doubleword/word
DX:AX
r/m16
AX
DX
-32,768 to +32,767
Quadword/doubleword
EDX:EAX
r/m32
EAX
EDX
-231
to 232 - 1
Non-integral results are truncated (chopped) towards 0. The sign of
the remainder is always the same as the sign of the dividend. The absolute
value of the remainder is always less than the absolute value of the divisor.
Overflow is indicated with the #DE (divide error) exception rather than
with the OF (overflow) flag.
Operation
IF SRC 0
THEN #DE; (* divide error *)
FI;
IF OpernadSize
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 OpernadSize
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;
ELSE (* 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;
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.
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.
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.
For details, see Volume 2A and Volume 2B of the Intel(R)
64 and IA-32 Intel Architecture Software Developer's Manual. For
the latest updates on the instruction set information, go to the
web site.
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