[PowerPC] Loading a value in a register

//Tutorial Created by BadLuckBrian
//No credit taken for this
//For sharing purposes only

In this tutorial i will show you how to set a register.

first, what is a register ?
A register is a variable which contains a value.

there is 32 registers (for us)


r0 - r31, we count the register 0 too so its 32 registers in total, there is also some other registers but i won't talk about them for now.
In PowerPC we will notice them like this: r0, r1, r2, r3 etc
Code:
r0 = old link register,  i won't talk about it for now
r1 = stack pointer, i won't talk about it for now
r2 = table of contents pointer, i won't talk about it for now

r3 = it can be used as the first argument of a function OR as the returned value from a function
r4–r10 = Used as the 2nd to the 8th arguments of a function.
r11 = used for the PS3 Syscalls
r12 = local var
r13-r31 = global var, we use them to store a value and being able to use it later on another function.
Don't worry we won't use them all, we will focus on r3, r4 and r5 for now :P



so in C# we can load values in variables like this:
Code:
int a = 10;
string b = "Bad Luck Brian";
byte[] c = new byte[] {0x05, 0x02, 0xFF};
in powerpc we use li and lis

registers are 4 bytes, 11 22 33 44
try to imagine them like this: XX XX YY YY



li - load imediate, it sets a register in the YY YY region

example: li r3, 0x15 ::: r3 = 00 00 00 15 (0x15 is the same as 0x0015)
Code:
li r3, 0x1500   ::: r3 = 00 00 15 00
now lis is the same but with the XX XX region
Code:
lis r3, 0x26   ::: r3 = 00 26 00 00
lis r3, 0x2600 ::: r3 = 26 00 00 00
lis r3, 0x216 ::: r3 = 02 16 00 00
Now we can set 2 bytes in a register, either the XX XX or the YY YY Region. We need to include some maths to set 4 bytes, its simple.

we will use addic and addis, addic adds something to the YY YY part and addis adds something to the XX XX Part.

we use them like this:
Code:
addic RESULT, REGISTER, VALUE
Result = register containing the result of the addition
Register = register to be added to the value
Value = value to be added to the register

in english it would translater to this: Result = Register + Value

lets use some examples:
Code:
li r3, 0x15
addic r3, r3, 0x01
r3 is now equal to: 0x16 (0x15 + 0x01)

now lets set r3 to: 0xFCA2801

first of all, lets put it in a XX XX YY YY format.

we start from the RIGHT separating them bytes after bytes
Code:
FCA2801
FCA28 01
FCA 28 01
F CA 28 01
we add a zero before the last value ('F') to reach the XX XX YY YY format
Code:
*************
*XX XX YY YY*
*0F CA 28 01*
*************
now i will use lis to set the XX XX part and addic to set the YY YY Part
Code:
lis r3, 0x0FCA            //r3 = 0F CA 00 00
addic r3, r3, 0x2801      //r3 = 0F CA 00 00  + 00 00 28 01   (0F CA 28 01)
lets do another example:

lets set r3 to: 0x1d60c

set it to the XX XX YY YY format to make it easier
Code:
1d60c
1d6 0c
1 d6 0c
add the zeros before it to reach XX XX YY YY
Code:
01 d6 0c
00 01 d6 0c

*************
*XX XX YY YY*
*00 01 d6 0c*
*************
now i will use lis to set the XX XX part and addic to set the YY YY Part
Code:
lis r3, 0x0001           //r3 = 00 01 00 00
addic r3, r3, 0xD60C     //r3 = 00 01 00 00  + 00 00 D6 0C  (00 01 D6 0C )

r3 = 0x0001D60c  or  0x1D60c
its simple !
in the next lesson i will teach you how to write in the memory :P