F6 /4         MUL r/m8         Unsigned multiply (AX ← AL * r/m8)

F7 /4         MUL r/m16         Unsigned multiply (DX:AX ← AX * r/m16)

F7 /4         MUL r/m32         Unsigned multiply (EDX:EAX ← EAX * r/m32)


Description

Performs an unsigned multiplication of the first operand (destination operand) and the second operand (source operand) and stores the result in the destination operand. The destination operand is an implied operand located in register AL, AX or EAX (depending on the size of the operand); the source operand is located in a general-purpose register or a memory location. The action of this instruction and the location of the result depends on the opcode and the operand size as shown in the following table.


Operand Size         Source 1         Source 2         Destination

Byte                 AL                 r/m8                 AX

Word                 AX                 r/m16                 DX:AX

Doubleword         EAX                 r/m32                 EDX:EAX


The result is stored in register AX, register pair DX:AX, or register pair EDX:EAX (depending on the operand size), with the high-order bits of the product contained in register AH, DX, or EDX, respectively. If the high-order bits of the product are 0, the CF and OF flags are cleared; otherwise, the flags are set.


Operands        Bytes                Clocks

r8                   2                  11   NP

r16                  2                    11   NP

r32                  2                    10   NP

mem8            2+d(0-2)         11   NP

mem16           2+d(0-2)         11   NP

mem32           2+d(0-2)          10   NP


implied           operand              result

multiplicand         (multiplier)

AL            *          byte               =  AX

AX            *          word               =  DX:AX

EAX           *          dword              =  EDX:EAX


Flags

The OF and CF flags are cleared to 0 if the upper half of the result is 0; otherwise, they are set to 1. The SF, ZF, AF, and PF flags are undefined.

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