shockrah/csnotes
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

fixed formatting for gitlab

Browse Source
This commit is contained in:
Medium Fries 2018-09-04 20:31:11 -07:00
parent 3fbaf3ce40
commit 171fe22b21
1 changed files with 21 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
cst337/lec/lec2.md
View File

@ -1,23 +1,27 @@
# lec2 # lec2
## Binary Bits & Bytes \ ## Binary Bits & Bytes
> Binary Notation 0b... \
> Binary Notation 0b...
Typically we see `0b` but sometimes like in many x86 assemblers we'll see `...b` to denote some bit string. Typically we see `0b` but sometimes like in many x86 assemblers we'll see `...b` to denote some bit string.
ost typically we deal with binary(when we do) in nibbles or 4 _bit_ chunks which then grouped into 2 groups of 4 to build up a byte.\ Most typically we deal with binary(when we do) in nibbles or 4 _bit_ chunks which then grouped into 2 groups of 4 to build up a byte.
Ex:`0101 1100` is a basic random byte. Ex:`0101 1100` is a basic random byte.
For most sane solutions this is essentially the only way we __ever__ deal with binary. For most sane solutions this is essentially the only way we __ever__ deal with binary.
## Two's Complement - aka Negate ## Two's Complement - aka Negate
To find the Negation of any bit-string: \ To find the Negation of any bit-string:
1. Flip all bits in the bit-string 1. Flip all bits in the bit-string
2. Add 1 to the bitstring 2. Add 1 to the bitstring
### Signedness ### Signedness
> Why? \ > Why?
Because this matters for dealing with `signed` and `unsigned` values. _No it doesn't mean positive and negative numbers._ Because this matters for dealing with `signed` and `unsigned` values. _No it doesn't mean positive and negative numbers._
Say we have 4 bites to mess with. This means we have a range of 0000 to 1111. If we wanted pureley positive numbers in this range we could have 0000 to 1111... or 0 to 15. Say we have 4 bites to mess with. This means we have a range of 0000 to 1111. If we wanted pureley positive numbers in this range we could have 0000 to 1111... or 0 to 15.
If we needed negative represenation however, we have to sacrifice some of our range. If we needed negative represenation however, we have to sacrifice some of our range.
@ -26,7 +30,8 @@ If it were 1 we would have a _signed_ number.
## Intro to hex ## Intro to hex
> Hex Notation 0x... \ > Hex Notation 0x...
x86 assemblersi(masm) will typically accept `...h` x86 assemblersi(masm) will typically accept `...h`
More convinient than binary for obvious reasons; namely it doesn't look like spaghetti on the screen. More convinient than binary for obvious reasons; namely it doesn't look like spaghetti on the screen.
@ -34,20 +39,26 @@ More convinient than binary for obvious reasons; namely it doesn't look like spa
Our 4-bit range from earlier {0000-1111} now becomes {00-ff}. Our 4-bit range from earlier {0000-1111} now becomes {00-ff}.
More pedantically our new hex range is 0x00 to 0xff. More pedantically our new hex range is 0x00 to 0xff.
> Binary mapped \ > Binary mapped
It happens that 1 nibble makes up 0x00 to 0xFF. It happens that 1 nibble makes up 0x00 to 0xFF.
So for now just get used to converting {0000-1111} to one of it's respective values in hex and evetually it should be second nature. So for now just get used to converting {0000-1111} to one of it's respective values in hex and evetually it should be second nature.
Then just move on to using hex(like immediately after these lessons). Then just move on to using hex(like immediately after these lessons).
Even the most obfuscated binary files out there don't resort to architectural obfuscation; until they do. Even the most obfuscated binary files out there don't resort to architectural obfuscation; until they do.
> Ascii in Hex Dumps \ > Ascii in Hex Dumps
Kind of a side note but most ascii text is from 0x21 to 0x66ish[citation needed] Kind of a side note but most ascii text is from 0x21 to 0x66ish[citation needed]
## 32 v 64 bit \ ## 32 v 64 bit
For those with a 32 bit background know that these notes deal with 64-bit architecutres mostly. So some quick terminology which might randomly throw you off anyway. For those with a 32 bit background know that these notes deal with 64-bit architecutres mostly. So some quick terminology which might randomly throw you off anyway.
> double-byte/ half-word \
> double-byte/ half-word
The latter is dumb but soemtimes used so wtever. The latter is dumb but soemtimes used so wtever.
> word = 4 bytes > word = 4 bytes
Etc onward with doubles, quads... Etc onward with doubles, quads...