Load/store instruction addressing mode of arm instruction set (2)

This note records the second kind of Load/Store The addressing mode of the instruction , These instructions refer to 1） The operand is half word （ Including signed and unsigned ） Of Load/Store Instructions ;2） Of signed byte data Load/Store Instructions ;3） Double character Load/Store Instructions .

The syntax format of the above instruction is as follows ：

LDR|STR{<cond>}H|SH|SB|D  <Rd>, <address_mode>

These instructions have the following addressing modes ：

	grammar	explain
1	[<Rn>, #+/-<offset_8>]	Immediate offset addressing
2	[<Rn>, +/-<Rm>]	Register offset addressing
3	[<Rn>, #+/-<offset_8>]!	Immediate pre update addressing
4	[<Rn>, #+/-<Rm>]!	Register pre update addressing
5	[<Rn>], #+/-<offset_8>	Immediate post update addressing
6	[<Rn>], +/-	Register post update addressing

Immediate offset addressing

[<Rn>, #+/-<offset_8>]

# 8 Bit immediate numbers are in high order 4 Bit and low 4 Bit separately encoded 
offset_8 = (immedH << 4) | immedL
if U == 1 then
	address = Rn + offset_8
else
	address = Rn - offset_8

Register offset addressing

[<Rn>, +/-<Rm>] 

if U == 1 then
	address = Rn + Rm
else
	address = Rn - Rm

Immediate pre update addressing

[<Rn>, #+/-<offset_8>]!

offset_8 = (immedH << 4) | immedL
if U == 1 then
   address = Rn + offset_8
else
   address = Rn - offset_8
if CondPassed then
   Rn = address

Register pre update addressing

[<Rn>, #+/-<Rm>]!

if U == 1 then
	address = Rn + Rm
else
	address = Rn - Rm
if CondPassed then
	Rn = address

Immediate post update addressing

[<Rn>], #+/-<offset_8>

address = Rn
offset_8 = (immedH << 4) | immedL
if CondPassed then
	if U == 1 then
		Rn = Rn + offset_8
	else
		Rn = Rn - offset_8

Register post update addressing

[<Rn>], +/-<Rm>

address = Rn
if CondPassed then
	if U == 1 then
		Rn = Rn + Rm
	else
		Rn = Rn - Rm