ARM指令集之乘法指令

ARM有两类乘法指令：一类指令的操作结果为32位，所以叫32位乘法指令；另一类的操作结果位64位，所以叫64位乘法指令。

为了运算高效，乘法指令要求所有操作数都位于寄存器中，所以ARM乘法指令无需指定寻址方式。

ARM共有如下乘法指令：

助记符	说明	实现逻辑
MUL	32位乘法指令	Rd = Rm * Rs
MLA	32位带加数的乘法指令	Rd = Rm * Rs + Rn
SMULL	64位有符号数乘法指令	RdHi = (Rm * Rs)[63:32]; RdLo = (Rm * Rs)[31:0];
SMLAL	64位带加数的有符号数乘法指令	RdLo = (Rm * Rs)[31:0] + RdLo; RdHi = (Rm * Rs)[63:32] + RdHi + CarryFrom((Rm * Rs)[31:0] + RdLo);
UMULL	64位无符号数乘法指令	RdHi = (Rm * Rs)[63:32]; RdLo = (Rm * Rs)[31:0];
UMLAL	64位带加数的无符号数乘法指令	RdLo = (Rm * Rs)[31:0] + RdLo; RdHi = (Rm * Rs)[63:32] + RdHi + CarryFrom((Rm * Rs)[31:0] + RdLo);

MUL

MUL{<cond>}{S} <Rd>, <Rm>, <Rs>

if ConditionPassed(cond) then
	Rd = (Rm * Rs)[31:0]
	if S == 1 then
		N Flag = Rd[31]
		Z Flag = if Rd == 0 then 1 else 0
		C Flag = unaffected
		V Flag = unaffected

MLA

MLA{<cond>}{S} <Rd>, <Rm>, <Rs>, <Rn>

if ConditionPassed(cond) then
	Rd = (Rm * Rs + Rn)[31:0]
	if S == 1 then
		N Flag = Rd[31]
		Z Flag = if Rd == 0 then 1 else 0
		C Flag = unaffected
		V Flag = unaffected

SMULL

SMULL{<cond>}{S} <RdLo>, <RdHi>, <Rm>, <Rs>, <Rn>

if ConditionPassed(cond) then
	RdHi = (Rm * Rs)[63:32] // 计算结果的高32位
	RdLo = (Rm * Rs)[31:0] // 计算结果的低32位
	if S == 1 then
		N Flag = RdHi[31]
		Z Flag = if RdHi == 0 and RdLo == 0 then 1 else 0
		C Flag = unaffected
		V Flag = unaffected

SMLAL

SMLAL{<cond>}{S} <RdLo>, <RdHi>, <Rm>, <Rs>, <Rn>

if ConditionPassed(cond) then
	RdLo = (Rm * Rs)[31:0] + RdLo
	RdHi = (Rm * Rs)[63:32] + RdHi + CarryFrom((Rm * Rs)[31:0] + RdLo)
	if S == 1 then
		N Flag = RdHi[31]
		Z Flag = if RdHi == 0 and RdLo == 0 then 1 else 0
		C Flag = unaffected
		V Flag = unaffected

UMULL

UMULL{<cond>}{S} <RdLo>, <RdHi>, <Rm>, <Rs>, <Rn>

if ConditionPassed(cond) then
	RdHi = (Rm * Rs)[63:32]
	RdLo = (Rm * Rs)[31:0]
	if S == 1 then
		N Flag = RdHi[31]
		Z Flag = if RdHi == 0 and RdLo == 0 then 1 else 0
		C Flag = unaffected
		V Flag = unaffected

UMLAL

UMLAL{<cond>}{S} <RdLo>, <RdHi>, <Rm>, <Rs>, <Rn>

if ConditionPassed(cond) then
	RdLo = (Rm * Rs)[31:0] + RdLo
	RdHi = (Rm * Rs)[63:32] + RdHi + CarryFrom((Rm * Rs)[31:0] + RdLo)
	if S == 1 then
		N Flag = RdHi[31]
		Z Flag = if RdHi == 0 and RdLo == 0 then 1 else 0
		C Flag = unaffected
		V Flag = unaffected