Intel 210200-002 manual Integer Multiply Imul

IMUL	INTEGER MULTIPLY IMUL
Operation:		Flags Affected:
(OEST) - (LSRC) * (RSRC) where		CF, OF
* is signed multiply		AF, PF, SF, ZF undefined
if (ext) = sign-extension of (LOW)
then (CF) - a

else (CF) -1 ; (OF) - (CF)

Description:

IMULsource

IMUL (Integer Multiply) performs a signed multiplication of the source operand and the accumulator. If the source is a byte, then it is multiplied by register AL, and the double- length result is returned in AH and AL. If the source is a word, then it is multiplied by register AX, and the double-length result is returned in registers DX and AX. If the upper

half of the result (AH for byte source, DX for word source) is not the sign extension of the lower half of the result, CF and OF are set; otherwise they are cleared. When CF and OF are set, they indicate that AH or DX contains significant digits of the result. The content of AF, PF, SF and ZF is undefined following exe- cution of IMUL.

Encoding:

11111 011 w 1mod 1 01 rIm 1

if w = 0 then LSRC = AL, RSRC = EA, OEST = AH, EXT = AH, LOW = AL else LSRC = AX, RSRC = EA, OEST = OX:AX, EXT = OX, LOW = AX

IMUL Operands	Clocks	Transfers	Bytes	IMUL Coding Example
reg8	80-98	-	2	IMULCL
reg16	128-154	-	2	IMUL BX
mem8	(86-104) + EA	1	2-4	IMUL RATE_BYTE
mem16	(138-164)+ EA	1	2-4	IMUL RATE_WORD [BP] [01]

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