iKlsR's Rant on Low Level Computing

Conversation started Nov 1, 2016 at 6:10.

iKlsR

Nov 1, 2016 06:10

I'm going to continue ranting for a bit, some stuff fresh in my mind.

Feel free to ignore anyone present.

I'd say I'm productive in C because I'm close to the hardware, that sounds like some cliche generic thing you'd hear but its true.

C is a very small language but has several quirks and older compilers can be annoying, (Dev C++, Borland circa 2007 anyone)

gandalf3

@iKlsR w... w.. ww... word???

ow....

iKlsR

Funny enough I never understood pointers for like 2 years until one day I read an article where they used physical addresses and it just clicked. Granted I had very limited resources a decade ago.

Getting back on track.

gandalf3

@someonewithpc Just explained pointers to me the other day

iKlsR

Anyone with basic computer knowledge should know that at the core processors are basically 1s and 0s.

gandalf3

Made everything much clearer (the syntax is really the most confusing part)

iKlsR

Nov 1, 2016 06:15

Some scattered bits here, lots of stuff on my mind now.

For a few years I used C and compilers and treated them like black boxes, ie I knew what X did but not how it did it.

@gandalf3 I'll give you a good explanation in a bit. Go uses pointers as well.

So one day I wondered, how does C work?

Languages don't really exist in a sense, they are interpreted (run in a virtual machine) or they are converted back to bytecode for the computer to run them linearly.

So your fancy loops and generators and closures in your high level language are for your ease of use. When the compiler is finished with it all the computers sees is 00 FA EC etc

So yeah, I did some research and found out some stuff.

Imagine a small hiearchy like this

Microcode -> Bytecode -> Assembly -> C -> (Python, blah blah blah)

And then below microcode imagine LOGIC GATES, transistors

and below that imagine the simplest thing or its complement, boolean algebra in a sense

AND | OR | XOR | NOT

this is what makes up your fancy i7

basically a circuit takes some input/current and turns bits (transistors on and off)

for example the arguably simplest computer you can build is a HALF ADDER

which is simply 3 gate to add two bits

very basic VERY VERY basic

it only gets complicated when you start looking at larger numbers, you make full adders, start adding 8 bit numbers etc, basic computer, add a timer (because these things run fast)

See

Programming my 8-bit breadboard computer

►

So yeah, in a nutshell to understanding C we somehow went back 50 years

we can now even make a 8 bit cpu in some logic program like logic.ly

you can even design your own and then program it as seen above

So yes, when Intel makes their processors they write in something called microcode and there is something even below that I think

these are hardcoded into the processor so when it sees certain sequences it does X, Y, Z

for FAST FAST access we have registers in the cpu, imagine these as temporary variables

we introduce new concepts like stack pointers, instruction pointer

at the core your cpu executes stuff linearly, your program of bytes is loaded into memory and the cpu executes the instructions in order, functions are simple jumps to another set of memory then back using the stack

So yeah, now who wants to write programs in bytecode / HEX, nobody thats who

remember early computers were programmed with switches and buttons, on off

then punchcards then basic languages with mnemonics that were still converted to bytecode

So introduce something like FORTRAN or lets just use assembly

microsofts dos .com is an exception I think, keeping this dumbed down and loose

So yh again these languages are just to make our life easier

so assembly MOV EAX, 12 puts the value 12 into a register for us to use later

that is easy for us to read, the computer as output from that will get whatever the OPCODE that stems from the MICROCODE corresponds to and perform some toggling of bits inside the cpu

But assembly is still hard to understand as shit

introduce C

C compiles down to assembly which in turn goes to bytecode

So that in a nutshell is how I can be efficient in C

I know assembly ( a bit ) or the basics of what it does.

I know the pipeline

And this is basically how old portable devices worked

The Game Boy, a hardware autopsy - Part 1: the CPU [PART 2 OUT NOW!]

►

instruction sets

thats how we can have emulators

blah blah blah

write a basic virtual machine

so yeah if you can break down what is happening under the hood you can get super productive

you can optimize your code directly via assembly, gcc -S file.c you will get assembly output, intel syntax is nice

Python is written in C

python is an interpreter, it also has its own special instruction set that then maps to a C runtime methinks

use python's dis module to get "assembly" output of your code, ever notice .pyc files? these are bytecode that ur file gets converted to to run very fast

Same for java .class files

bytecode that the JVM (remember this above) runs

Python and Java are more protable than C because they provide a layer that runs their specific bytecode as opposed to raw C that generates for the architecture you are on hence why you have to recompile

Then we get cute things like ELF and PE file formats

etc etc

END RANT

gandalf3

Nov 1, 2016 06:36

s/rant/book/

iKlsR

I wrote a bit about blackboxes here ricardolovelace.com/vim-is-not-a-black-box.html

using Vim as an example

If anyone is generally interested in this, I can go for hours.

This is how you get to be a good programmer, breaking down a problem into tiny digestable bits.

Understand something at its core and you're suddenly in control.

Once you get the connection everything you've ever read or learnt falls into place, logic gates, algebra, circuits etc

For example you might wonder how a touch screen works?

remember... 1s and 0s

there are many types but the most common is capacitive

behind this thin layer we have a flat bed of inputs that are say set to 0

swipe you turn on some and this motion gets translated into some movement that then uses to execute some motion

same thing applies to Infrared

you can easily reverse engineer your home remote with a breadboard, arduino and a IR sensor

So yeah. I can be productive in C.

Thanks.

and PHP is written in C

aha!

php is in itself a framework already for C in a sense so PHP frameworks are already on a framework layer

AND ALL OF THIS APPLIES EVERYWHERE

web, packets?? 1s and 0s

UDP TCP are simply sets of bytes

your Wifi

For anyone who has seen the matrix, when Neo understands and starts seeing the matrix for what it is, a simulation/code. That is how your eyes will open when you understand that everything computing is 1s and 0s.

quantum computing is another good rant where we can have super states

schrodinger, time crystals? maybe some space civilization out there with there advanced tech uses 10 base digits instead of 2

that could make our fastest processor look like a chip in a smart fan

so to repeat myself, once it clicks the possibilities are endless

Pointers

C syntax

We declare a pointer like this int gift = &present;

Quick fact, did you know you can have a pointer to a pointer to a pointer ... int ***a, uses are not so useful tho.

So a pointer simply points to the address of another variable.

Say present = 5;

Lets look at our program in memory

see that gift holds the address of present

this means that if present is changed, the address will remain the same regardless, it already has its position in memory on the stack.

gift will always have the address of present

to get the value at that address we use the dereference operator *

so *gift = 5;

while gift = 0001;

we use the reference operator to get addresses

this is more powerful in C++ a bit...

you might have also heard about copying by value vs copying by reference

so yeah what is the point of pointers

these are mostly used to allocate memory

when you run your program there is a part of it that has space for your declared vars and that is limited

so local variables are declared on something called the stack

pointers are on the heap (global memory)

we tell pointers to go into ram and secure memory as needed

malloc

new

dynamic!

when we are done with this additional requested memory we should free it (return it back to the os) so other apps can use

delete

free

hope that gives a bit more context @gandalf3

1s and 0s...

gandalf3

Nov 1, 2016 07:00

yes, that all makes sense

iKlsR

A real life example would probably be buying a house and having to take a loan from the bank.

Conversation ended Nov 1, 2016 at 7:01.

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