Data Types

Size of Data Types:
	Byte 		  - 8bits
	Word 		  - 16bits
	Double Word 	  - 32bits
	Quad Word 	  - 64bits
	Double Quad Words - 128bits


	Each Data Type can be unsigned or signed.
	EX.
		unsigned Doube Word is 32 bits long and will use all 31(0-31) bits for the value
		signed Double Word is also 32 bits long and will use all 30(0-30) bits for the value and the last 			bit for the sign (Can be +/-)



LITTLE INDIAN:


	Lower Byte gets stored in lower memory.

	EX.
		Lets say we have byte 0x12345678
		In memory we would see 0x78 0x56 0x34 0x12
		It reverses the order we see it but the data stays the same

	EX 2.

		0A 0B 0C 0D       Memory - Lower Half
		 |  |  |  |-----> | 0D |
		 |  |  |--------> | 0C |
		 |  |-----------> | 0B |
		 |--------------> | 0A | 
					 - Higher Half


	--------------INITALIZED DATA TYPES----------------------

LABLES:

	Accessing a lable in NASM be aware of the following (Case Sensative!!!)
		Accessing memory reference with [] AKA the value
		- message db 0XAA, 0xBB, 0xCC, 0xDD
		- mov eax, message <- moves address into eax
		- mov eax, [message] <- moves the value into eax


Define Byte (db):
	Define Byte is normally use for a single byte and define word is used for 2.

	EX.
		db 0x55 	        ; Can use single bytes
		db 0x55, 0x56, 0x57     ; Can also use a sequence of bytes
		db 'a', 0x55            ; Can also use chars
		db 'hello', 13, 10, '$' ; Can also use strings


Define Word (dw):

	Define Word will alays use the full amount of space avaliable, This applys for all other DATA Types, for 		example
		dw 'a' ; This will show 0x61 0x00, 61 is ascii for lowercase a and the 0x00 is a filler

	EX.
		dw 'ab' ; This will show 0x61 0x62
		dw 'abc' ; This will show 0x61 0x62 0x63 0x00


Define Double Word (dd):

	EX.
		dd 0x12345678 ; This will show 0x78 0x56 0x34 0x12 (remember little indeian)
		dd 1.234567e20 ; Floating point constant


Double Quad Word (dq):

	EX.
		dq 0x123456789abcdef0 ; 8 byte constant
		dq 1.234567e20	      ; double-percision float

Double Extended-percision floating point (dt):

	EX.
		dt 1.234567e20 ; extended percision float


	--------------UNNITALIZED DATA TYPES----------------------

				NOTE: All unitialized data is uder .BSS in ASM file

Buffer:

	EX.
		resb 64 ; This will reserve 64 bytes

Wordvar:

	EX.
		resw 1 ; this will reserve a word




	--------------SPECIAL TOKENS----------------------


$:
	This evaluates to the current line
	Most of the time used to find an offset of a current instruction

	EX.
		message: db "Hellow World" ; Defines the byte Hello World
		mlen equ $-message         ; this gets the length of the string 

	When looking at the example above we see the following:

		message: db "Hello World"<-----| AKA right after d is this case
		Once this line exucuted $ is = |

		In this line, mlen equ $-message, message is = right before 'H' so this must = the length of the 			string
		

$$:
	This evaluates to the beginning of the current section



Times (times):

	This is nothing more than exicuting an instruction multple times
	This also cn apply to data as well as instructions.

	EX.
		DATA:
		zerobuf: times 64 db 0
		(Repeat the commands "db 0" 64 times)

		INSTRUCTIONS
		times 100 movsb
		(Repeat the instruction "movsb" 100 times)



Moving Values:

	- message db 0xAA, 0xBB, 0xCC, 0xDD ; assigns the data to the label message
	- mov eax, message ; this moves the address of the label message to EAX
	- mov eax, [message] ; this moves the actual value  AKA "0xAA, 0xBB, 0xCC, 0xDD" into EAX