Slide 14.11: Calling C/C++ functions(Cont.) Slide 15.2: MUL instruction Home

Multiplication and Division Instructions

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The Intel instruction set lets you multiply and divide 8-, 16-, and 32- bit integers, using the instructions on the right.

Command Description MUL Unsigned multiply IMUL Signed multiply DIV Unsigned divide IDIV Signed divide

MUL Instruction

The MUL (unsigned multiply) instruction comes in three versions: multiplies an 8-bit operand by AL, multiplies a 16-bit operand by AX, and multiplies a 32-bit operand by EAX.

Multiplicand Multiplier Product AL r/m8 AX AX r/m16 DX:AX EAX r/m32 EDX:EAX

The multiplier and multiplicand are the same size, and the product is twice their size. Because the destination operand is twice the size of the multiplicand and multiplier, overflow can not occur.

MUL — Unsigned Multiply

Usage: mul src Flag O D I S Z A P C Result *     ? ? ? ? * Unsigned multiply of the accumulator by the source. If “src” is a byte value, then AL is used as the other multiplicand and the result is placed in AX. If “src” is a word value, then AX is multiplied by “src” and DX:AX receives the result. If “src” is a double word value, then EAX is multiplied by “src” and EDX:EAX receives the result. Clocks Operands 286 386 486 Size Bytes reg8 13 9-14 13-18 2 reg16 21 9-22 13-26 2 reg32   9-38 13-42 2-4 mem8 16 12-17 13-18 2-4 mem16 24 13-26 12-25 2-4 mem32   12-21 13-42 2-4