Intel 80C186XL, 80C188XL Shift Logical Left, Shift Arithmetic Left, Shift Arithmetic Right

INSTRUCTION SET DESCRIPTIONS

Table C-4. Instruction Set (Continued)

Name	Description		Operation	Flags
				Affected
SHL	Shift Logical Left:		(temp) ← count	AF ?
SAL	Shift Arithmetic Left:		do while (temp) ≠ 0	CF
	SHL dest, count		(CF) ← high-order bit of (dest)	DF –
			(dest) ← (dest) × 2	IF –
	SAL dest, count
			(temp) ← (temp) – 1	OF
	Shifts the destination byte or word left
			if	PF
	by the number of bits specified in the
			count = 1	SF
	count operand. Zeros are shifted in on
			then	TF –
	the right. If the sign bit retains its
			if	ZF ¸
	original value, then OF is cleared.		high-order bit of (dest) ≠ (CE)
	Instruction Operands:
			then
	SHL reg, n	SAL reg, n	(OF) ← 1
	SHL mem, n	SAL mem, n	else
	SHL reg, CL	SAL reg, CL	(OF) ← 0
	SHL mem, CL	SAL mem, CL	else
			(OF) undefined
SAR	Shift Arithmetic Right:		(temp) ← count	AF ?
	SAR dest, count		do while (temp) ≠ 0	CF
			(CF) ← low-order bit of (dest)	DF –
	Shifts the bits in the destination
			(dest) ← (dest) / 2	IF –
	operand (byte or word) to the right by
			(temp) ← (temp) – 1	OF
	the number of bits specified in the
			if	PF
	count operand. Bits equal to the
			count = 1	SF
	original high-order (sign) bit are shifted
			then	TF –
	in on the left, preserving the sign of the
			if	ZF ¸
	original value. Note that SAR does not		high-order bit of (dest) ≠
	produce the same result as the
			next-to-high-order bit of (dest)
	dividend of an "equivalent" IDIV
			then
	instruction if the destination operand is
			(OF) ← 1
	negative and 1 bits are shifted out. For
			else
	example, shifting –5 right by one bit
			(OF) ← 0
	yields –3, while integer division –5 by 2
			else
	yields –2. The difference in the instruc-
			(OF) ← 0
	tions is that IDIV truncates all numbers
	toward zero, while SAR truncates
	positive numbers toward zero and
	negative numbers toward negative
	infinity.
	Instruction Operands:
	SAR reg, n
	SAR mem, n
	SAR reg, CL
	SAR mem, CL

NOTE: The three symbols used in the Flags Affected column are defined as follows:

–the contents of the flag remain unchanged after the instruction is executed ¸? the contents of the flag is undefined after the instruction is executed

the flag is updated after the instruction is executed

C-40