Slide 15.4: IMUL instruction (cont.)

IMUL Instruction (Cont.)

Two-operand formats: Store the product in the first operand. The first operand must be a register. The second operand can be a register, memory operand, or immediate value.

Three-operand formats: Store the product in the first operand.

Two- and three- operand formats truncate the product to the length of the destination. If significant digits are lost, the Overflow and Carry flags are set.

8-Bit Signed Multiplication	8-Bit Signed Multiplication	3-Operand Multiplication
.data x SBYTE -02h y SBYTE 40h .code mov al, x imul y call DumpRegs	.data x SBYTE -03h y SBYTE 40h .code mov al, x imul y call DumpRegs	.data x SWORD 20h .code imul bx, x, 400h call DumpRegs
Output	Output	Output
AX= CF= OF=	AX= CF= OF=	BX= CF= OF=
3-Operand Multiplication	2-Operand Multiplication	32-Bit Signed Multiplication
.data x SWORD -200h .code movsx eax, x imul ebx, eax, 0400h call DumpRegs	.data x SDWORD 200h y SDWORD 400h .code mov ecx, x mov ebx, y imul ecx, ebx call DumpRegs	.data x SDWORD -200h y SDWORD 400h .code mov eax, x mov ebx, y imul ebx call DumpRegs
Output	Output	Output
EBX= CF= OF=	ECX= CF= OF=	EDX:EAX= CF= OF=