IMUL Multiplication, Signed Flags: O D I T S Z A P C
* - - - ? ? ? ? *
IMUL performs a signed multiplication. This instruction has 3
variations:
i) One-operand form IMUL source
Logic AX ← AL * source
or
DX:AX ← AX * source
or
EDX:EAX ← EAX * source ; 386+
The source can be a byte, word, or doubleword located in
memory or in a general register.
ii) Two-operand form IMUL oper1,oper2 CPU: 186+/386+
Logic oper1 ← oper1 * oper2
The first operand can be in any general register while the
second operand can be an immediate value (80186+), or a value
in memory or a general register (80386+). The product replaces
the first operand.
iii) Three-operand form IMUL dest,oper1,oper2 CPU: 186+
Logic dest ← oper1 * oper2
The second operand (oper1) can be in any general register or a
value in memory while the third operand (oper2) must be an
immediate value. The product is stored in destination which
can be any general register.
Note
An immediate value used with IMUL is automatically sign-extended
to match the size of the general register operand.
IMUL clears the carry and overflow flags (CF and OF) under these
conditions:
- form i : if the upper half of the destination does not contain
any significant digits of the result
- form ii,iii: if the result fits within the size of the destination
(otherwise CF and OF are set to 1).
Opcode Format
F6 /5 IMUL r/m8
F7 /5 IMUL r/m16
F7 /5 IMUL r/m32 ; 386+
0F AF /r IMUL r16,r/m16 ; 386+
0F AF /r IMUL r32,r/m32 ; 386+
69 /r iw IMUL r16,imm16 ; 186+
69 /r iw IMUL r16,r/m16,imm16 ; 186+
69 /r id IMUL r32,imm32 ; 386+
69 /r id IMUL r32,r/m32,imm32 ; 386+
6B /r ib IMUL r16,imm8 ; 186+
6B /r ib IMUL r16,r/m16,imm8 ; 186+
6B /r ib IMUL r32,imm8 ; 386+
6B /r ib IMUL r32,r/m32,imm8 ; 386+
Length and timing
Accumulator multiplies
Operands Bytes 8088 186 286 386 486 Pentium
r8 2 80-98 25-28 13 9-14 13-18 11 NP
r16 2 128-154 34-37 21 9-22 13-26 11 NP
r32 2 - - - 9-38 13-42 10 NP
mem8 2+d(0-2) 86-104+EA 32-34 16 12-17 13-18 11 NP
mem16 2+d(0-2) 134-160+EA 40-43 24 12-25 13-26 11 NP
mem32 2+d(0-2) - - - 12-41 13-42 10 NP
2 and 3 operand multiplies
Operands Bytes 186 286 386 486 Pentium
r16, imm 2+i(1,2) - 21 9-14/9-22 13-18/13-26 10 NP
r32, imm 2+i(1,2) - - 9-38 13-42 10 NP
r16,r16,imm 2+i(1,2) 22/29 21 9-14/9-22 13-18/13-26 10 NP
r32,r32,imm 2+i(1,2) - - 9-38 13-42 10 NP
r16,m16,imm 2+d(0-2) 25/32 24 12-17/12-25 13-18/13-26 10 NP
+i(1,2)
r32,m32,imm 2+d(0-2)+i(1,2) - 12-41 13-42 10 NP
r16, r16 2+i(1,2) - - 9-22 13-18/13-26 10 NP
r32, r32 2+i(1,2) - - 9-38 13-42 10 NP
r16, m16 2+d(0-2)+i(1,2) - 12-25 13-18/13-26 10 NP
r32, m32 2+d(0-2)+i(1,2) - 12-41 13-42 10 NP
All forms: dest, src cycles for: byte/word
or dword
dest, src1, src2