CS208 Introduction to Computer Systems
Wednesday, 17 January 2024

+ Queues questions

+ Questions we want to answer
Note that "= ?" in these examples means "represents what integer?"

    0101 = ?   if it's just a binary number
    0101 = ?   if it's a 4-bit 2's complement representation of a number
    1100 = ?   binary
    1100 = ?   4-bit 2's comp

    00011001 = ?  binary
    00011001 = ?  8-bit 2's comp
    0x19 = ?      hexadecimal
    0x19 = ?      8-bit 2's comp

    11111010 = ?  binary
    11111010 = ?  8-bit 2's comp

    0xFA = ?      hexadecimal
    0xFA = ?      8-bit 2's comp

    0xFFFA = ?       16-bit 2's comp
    0xFFFFFFFA = ?   32-bit 2's comp

+ Notes
- Integers are integers. There are an infinite number of them.
    They're our old friends: ...-3, -2, -1, 0, 1, 2, 3,...
- We have a bunch of ways of writing integers down on paper
    (decimal, binary, octal, hexadecimal); for negative integers,
    we stick a minus sign in front
- Those ways of writing integers I just mentioned? They apply
    to any integer, no matter how big, limited only by our supply
    of paper and ink or stone and chisel etc.
- Those aren't the only ways of writing integers. (Could you use
    DNA-editing techniques to write integers in molecule form? Yes!)
- If we say "all we have is a bunch of two-state devices and we
    want to write integers using those devices", we can use ordinary
    binary to handle positive integers, but we're gonna need a
    trick to help us represent negative integers.
- Several common tricks exist (https://en.wikipedia.org/wiki/Signed_number_representations)
    "signed magnitude"
    "excess-K" (also know as "offset-K", "bias-K")
    "one's complement"
    "two's complement"   <---- BY FAR THE MOST COMMONLY USED ----

+ Summary of techniques
- Given a hex representation of a 32-bit bit pattern,
    write it out as bits
- Given a hex representation of a 32-bit bit pattern,
    determine what integer the bits represent if they're
    interpreted using the 32-bit two's complement scheme
- Given a hex representation of a 32-bit bit pattern,
    determine which ASCII characters those bits represent
- Given a 32-bit bit pattern and the integer N the bits represent
    using the two's complement scheme, what bit pattern represents
    the negation -N?

+ Look at it in C
- sizeof(char), sizeof(short), sizeof(int), sizeof(long)
- experiments with int variables and printf
- experiments with char variables and printf (WTH?!!)