machine code

[humanguy]

Hello. I'm wondering when viewing and editing machine code ( ones and zeros ) would be necessary. At my job, the lowest level viewing and editing is done with a hex editor. From my research, it appears that that is pretty much the lowest level editor used by most computer professionals. Is it possible to view and edit a single bit in a hex editor? And what would be the reason for it? Thanks.

 

[humanguy]

I think I figured out the answer. I was forgetting that the character encodings we humans use to represent information are made up of a 'group' of bits - therefore editing a single bit would be overkill. Of course it could be possible to have an editor made up of ones and zeros, but, since characters are encodings based on groups of bits, using a hex editor for shorthand makes sense. Onward and upward

 

[Nanopants]

Hello. I'm wondering when viewing and editing machine code ( ones and zeros ) would be necessary. At my job, the lowest level viewing and editing is done with a hex editor. From my research, it appears that that is pretty much the lowest level editor used by most computer professionals. Is it possible to view and edit a single bit in a hex editor? And what would be the reason for it? Thanks.

Flags (boolean values) are often stored as single bits for efficiency. If you can arrange these bits in a meaningful order, then you can reinterpret them as a numerical value and perform mathematical operations on all flags stored in a single word at once (32 or 64), instead of retrieving one flag at a time from memory. That's useful if for example you want to quickly sort subsets of boolean values.

You can retrieve the value of a single bit by using something called a bit mask and a logical operation. Say for example you have a byte containing 0011 1100, but all you want is the value of the fourth bit from the right. So you would use a mask value of 0000 1000, use an AND bitwise operation with the original byte, and the result is 0000 1000, which may be interpreted as equivalent to true or one (because it is non-zero). Had the original byte been 0011 0100, the result would be zero, or false.

This isn't exactly machine code. Yes it is closely related to how the machine works with data but the concepts of bit manipulation are fairly fundamental for any programming language that will allow you to play around with them. Machine code is practically unreadable.