Assembly question

I starting to learning assembly,and really insterested to read "The art of assembly language Programming" but stuck in chapter 1.6 "Logical Operations on Binary Numbers and Bit Strings"

Here is the text from the book:

This bitwise logical AND operation would force the H.O. four bits to zero and pass the L.O. four bits of 'X' through unchanged. Likewise you could force the L.O. bit of 'X' to one and invert bit number two of 'X' by logically ORing 'X' with 0000 0001 and logically exclusive-ORing 'X' with 0000 0100 respectively. Using the logical AND OR and XOR operations to manipulate bit strings in this fashion is know as masking bit strings. We use the term masking because we can use certain values (one for AND zero for OR/XOR) to 'mask out' certain bits from the operation when forcing bits to zero one or their inverse.

Online book was here:

http://oopweb.com/Assembly/Documents/ArtOfAssembly/VolumeFrames.html

The question is:
- what the hell is "0ring???
- and i am a bit miss understand in this text.would someone explain me by an example operation?

[peleon]

Hello 3ch0,

First, I have to admit that book mess up a lot what AND/OR/XOR is. It's a simple concept that is hidden in that text line

About ORing, well, I guess the the author wants to say OR-ing (verb finished in -ing) (that磗 english i suppose ). So, that's the same as saying: "Apply the OR operator..."

My explanation about this:

OR = binary add

0 or 0 = 0
1 or 0 = 1
0 or 1 = 1
1 or 1 = 1

AND = binary multiply

0 and 0 = 0
0 and 1 = 0
1 and 0 = 0
1 and 1 = 1

XOR = exclusive OR

0 xor 0 = 0
0 xor 1 = 1
1 xor 0 = 1
1 xor 1 = 0

So, using this 3 operators you can play with the bits in a registry/memory as you like. For example, suppose that you have in the EAX register a value. If you want to know if that number is odd or even you can make the following:

and eax, 1 ; will leave the bit-0 untouched to check if even or odd

.if eax == 1

; we are odd!

.else

; we are even!

.endif

Hope this helps

thanks,i got it.so exclusive 0ring suppose be xor right?
the book was really good!!.did you knew any other basic assembly book?

[peleon]

Yes, you are right.

About books...well, I dont know any other online book. You have plenty of tutorials on the net. Also, when you know the basics of assembly, you just need the Intel Instruction set manual to know all the different instructions to play with

Regards

does the book explained good enough for basic assembly?.and how did you take for mastering assembly?

[peleon]

i'm not a asm guru...but for those of you who start learning ASM, my advice is to make small examples in asm and debug them under a debugger. It's when you see the registers/memory "changing" under the debugger, when you start getting a solid knowledge in asm.