IMUL  Rb      {Rb/Ms} B/w  011010s1 MdRegR/m {disp}   {disp}	data	 {data}



For constants, use the following 32bit MASM code:

mMulC MACRO pDest, pSrc, pConst
IF pConst EQ 2
	FIDNI pDest, pSrc
	shl pDest, 1
	ELSE
	lea pDest, [pSrc*2]
		ENDIF
ELSEIF pConst EQ 3
	lea pDest, [pSrc*2+pSrc]
ELSEIF pConst EQ 4
	;SHL pDest, 2 ;lea is faster
	lea pDest, [pSrc*4]
ELSEIF pConst EQ 5
	lea pDest, [pSrc*4+pSrc]
ELSEIF pConst EQ 6
	lea pDest, [pSrc*2+pSrc]	;Src x3
	shl pDest, 1			;(Src X3) x2
ELSEIF pConst EQ 7
	IFIDNI pDest, pSrc
	;if I can't get back to pSrc after
	;overwriteing pDest (i.e. pDest is pSrc
	imul pdest, pSrc, pConst
	ELSE
	;Thanks Tim Roberts, timr@probo.com
	lea pDest, [pSrc*8]
	sub pDest, pSrc
		ENDIF
ELSEIF pConst EQ 8
	lea pDest, [pSrc*8]
ELSEIF pConst EQ 9
	lea pDest, [pSrc*8+pSrc]
ELSEIF pConst EQ 10
	lea pDest, [pSrc*4+pSrc]	;Src x5
	shl pDest, 1			;(Src X5) x2
ELSEIF pConst EQ 11
	IFIDNI pDest, pSrc
	imul pdest, pSrc, pConst
	ELSE
	lea pDest, [pSrc*4+pSrc]	;Src x5
	shl pDest, 1			;(Src X5) x2
	add pDest, pSrc			;((Src x5) x2) + Src
		ENDIF
ELSEIF pConst EQ 12
	lea pDest, [pSrc*2+pSrc]	;Src x3
	lea pDest, [pDest*4]		;(Src x3) x4
ELSEIF pConst EQ 13
	IFIDNI pDest, pSrc
	imul pdest, pSrc, pConst
	ELSE
	;Thanks Tim Roberts, timr@probo.com
	lea pDest, [pSrc*4+pSrc] ; src x 5
	lea pDest, [pSrc*8+pDest] ; src x 13
		ENDIF
ELSEIF pConst EQ 15
	lea pDest, [pSrc*4+pSrc]	;Src x5
	lea pDest, [pDest*2+pDest]	;(Src x5) x3
ELSEIF pConst EQ 16
	IFIDNI pDest, pSrc
	shl pDest, 2
	ELSE
	lea pDest, [pSrc*8]		;Src x8
	shl pDest, 1			;(Src X8) x2
		ENDIF
ELSEIF pConst EQ 17
	IFIDNI pDest, pSrc
	imul pdest, pSrc, pConst
	ELSE
	;Thanks Tim Roberts, timr@probo.com
	lea pDest, [pSrc*8]
	lea pDest, [pDest*2+pSrc]
		ENDIF
ELSEIF pConst EQ 18
	lea pDest, [pSrc*8+pSrc]
	shl pDest, 1			;(Src X9) x2
ELSEIF pConst EQ 19
	IFIDNI pDest, pSrc
	imul pdest, pSrc, pConst
	ELSE
	lea pDest, [pSrc*8]		;Src x8
	shl pDest, 1			;(Src X8) x2
	add pDest, pSrc			;((Src x8) x2) + Src
		ENDIF
ELSEIF pConst EQ 20
	lea pDest, [pSrc*4+pSrc]	;Src x5
	lea pDest, [pDest*4]		;(Src x5) x4
ELSEIF pConst EQ 24
	lea pDest, [pSrc*2+pSrc]	;Src x3
	lea pDest, [pDest*8]		;(Src x3) x8
ELSEIF pConst EQ 25
	lea pDest, [pSrc*4+pSrc]	;Src x5
	lea pDest, [pDest*4+pDest];(Src x5) x5
ELSEIF pConst EQ 30
	lea pDest, [pSrc*4+pSrc]	;Src x5
	shl pDest, 1			;(Src X5) x2
	lea pDest, [pDest*2+pDest]	;((Src x5) x2) x3
ELSE
	imul pdest, pSrc, pConst
	ENDIF
	ENDM

Note: On the Pentium II's imul may actually be as fast or faster! This macro is good for older chips.

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