54 lines
2.2 KiB
Markdown
54 lines
2.2 KiB
Markdown
# lec2
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## Binary Bits & Bytes \
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> Binary Notation 0b... \
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Typically we see `0b` but sometimes like in many x86 assemblers we'll see `...b` to denote some bit string.
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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.\
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Ex:`0101 1100` is a basic random byte.
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For most sane solutions this is essentially the only way we __ever__ deal with binary.
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## Two's Complement - aka Negate
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To find the Negation of any bit-string: \
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1. Flip all bits in the bit-string
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2. Add 1 to the bitstring
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### Signedness
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> Why? \
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Because this matters for dealing with `signed` and `unsigned` values. _No it doesn't mean positive and negative numbers._
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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.
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If we needed negative represenation however, we have to sacrifice some of our range.
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Our new unsigned range is 0-7. We say it's unsigned because the first bit here is 0.
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If it were 1 we would have a _signed_ number.
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## Intro to hex
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> Hex Notation 0x... \
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x86 assemblersi(masm) will typically accept `...h`
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More convinient than binary for obvious reasons; namely it doesn't look like spaghetti on the screen.
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Our 4-bit range from earlier {0000-1111} now becomes {00-ff}.
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More pedantically our new hex range is 0x00 to 0xff.
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> Binary mapped \
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It happens that 1 nibble makes up 0x00 to 0xFF.
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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.
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Then just move on to using hex(like immediately after these lessons).
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Even the most obfuscated binary files out there don't resort to architectural obfuscation; until they do.
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> Ascii in Hex Dumps \
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Kind of a side note but most ascii text is from 0x21 to 0x66ish[citation needed]
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## 32 v 64 bit \
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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.
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> double-byte/ half-word \
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The latter is dumb but soemtimes used so wtever.
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> word = 4 bytes
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Etc onward with doubles, quads...
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