Code Optimization

Hello,

Today we are going to learn how to apply mask to any type of data. We will look into mask itself, and apply a mask to an image.

Lets look into the image below to get general idea of mask:

As you can see we took the star mask and an image and got imaged star in output. Cool? :)

Hmm, what is going on and how to do it? Everything is very simple if you have learned my post about bit manipulations.

So, to do it we need the following things:

- bit mask;

- an image;

- go through each byte and apply AND operation for each couple of bytes (actually Int32 in my case as it is much faster).

Here is how:

Int32[] rgba_source = new Int32[256 * 256];
Int32[] rgba_dest = new Int32[256 * 256];

for (int i = 0; i < rgba_source.Length; i++)
{
    rgba_dest[i] = rgba_dest[i] & rgba_source[i];
}

Here is the result of masking two images:

That's it, you have got like textured object/figure :).

Now, just imagine where you can use such approach and with which kind of data, as well as other operations like XOR and OR.

In short - it can be used in hash, crypto, visualization algorithms and much more.

One easiest encryption algorithm is just apply XOR for each char of string, for example:

string origin = "hello world";
string encoded = string.Empty;
string decoded = string.Empty;

for (int i = 0; i < origin.Length; i++)
{
    encoded += (char)(origin[i] ^ 0x003F);
}

And we will get "WZSSPHPMS[" in the encoded variable, that is equal to hello world but just encoded. To decrypt/decode it, just make the same XOR:

for (int i = 0; i < encoded.Length; i++)
{
    decoded += (char)(encoded[i] ^ 0x003F);
}

And you got your "hello world" string back again in the decoded variable.

Think about it and a lot of things you can do with that ;)

Thank you and see you next time.

1vqHSTrq1GEoEF7QsL8dhmJfRMDVxhv2y

Hi,

Today, I will explain bit manipulations. As you know each bit set in its own position from 0 to 7.

As an example, Lets use the following byte 00000010 which is 0x02 in hex-decimal and 2 in decimal.

It has "1" at 1st place (lets count it from zero place to 7 place).

So shifting bits to the left will move all bits to the left:

00000010 << 2 = 00001000

As you see now 1 on the 3rd place, instead of 1st place, because of we have shifted all bits to the left 2 times. Same rule is for the right shifting.

Another type of bit manipulation is boolean operations like XOR, OR and AND.

OR just sets 1 on its place:

0010 OR 0001 = 0011
0010 OR 0010 = 0010

XOR makes the same as OR and inverts bits at the same places if they both equal to 1  (outputs 1 only when both bits differ):

0010 XOR 0001 = 0011
0010 XOR 0010 = 0000

AND leaves bits that equal to 1 at the same place only:

Rectangle rect = new Rectangle(0, 0, tmpi.Width, tmpi.Height);
BitmapData bmpd = tmpi.LockBits(rect, ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);
Int32[] src = new Int32[bmpd.Stride / 4 * tmpi.Height];
System.Runtime.InteropServices.Marshal.Copy(bmpd.Scan0, src, 0, src.Length);

public void SetPointAsIs(byte r, byte g, byte b, byte a, int x, int y)
{
    src[Stride * Y + x] = (a << 24) + (r << 16) + (g << 8) + b;
}
public ColorBgra GetPoint(int x, int y)
{
    Int32 argb = src[Stride * y + x];
    ColorBgra c = new ColorBgra();
    c.A = (byte)(argb >> 24);
    c.R = (byte)(argb >> 16 & 0xff);
    c.G = (byte)(argb >> 8 & 0xff);
    c.B = (byte)(argb & 0xff);
    return c;
}

1vqHSTrq1GEoEF7QsL8dhmJfRMDVxhv2y

Hello,

As I said we would go from basic to complex things step by step and this post will clarify some important things that you must know about hardware and bits.

Each PC consists of different devices like monitor, HDD, keyboard, mouse, etc., and each device has its own controller (a chip) that controls device. For example, mouse has a small chip that controls laser and gets and sends commands and data to and from PC.

Almost each device has its own IRQ - this is interrupt number that assigned to a device by system to be able to get and send commands. So when you move your mouse it triggers a IRQ and provides data like DX and DY and system knows what direction should it move a cursor to and how many points the cursor should be moved.

This is general explanation and to be able to understand more you have to find a book and read it.

So devices talk to each other or to system via Bytes. They send a lot of bytes and each byte consists of 8 bits, like:

...

0 0 0 0   0 0 0 0

0 1 1 0   1 1 1 1

...

To understand what these bits represent in a more human readable way you have to know how to convert binary numeral system into hex-decimal or decimal numeral system. You can find it on internet or a book.

So, when I started to learn programming my first language was Assembler for Z-80 CPU. There was a book that had description for all 255 op-codes (commands of CPU) and some additional information, but it was not enough for me to understand anything and more over to create at least such simple program like the popular "Hello World!".

I did learn bits, bytes, bit operations like shift to the left/right, conditional operations like jump here or there, CPU registers, etc. And that was much but not enough to make the "Hello World!".

Then I did figure out memory structure (my brother did help me in this) and at some point there was like a flash in my mind - "Or God! That is how it all works!".

Main thing is to understand memory structure and how controllers works. In my case I had video memory mapped from 16384 address to 32767, and one part of this memory did represent pixels, and another part - colors.

Filling just pixel memory with correct bits will lead to this:

that is represented by bits:

1 1 0 0 1 1 0 0    = 0xCC
1 1 0 0 1 1 0 0    = 0xCC
1 1 0 0 1 1 0 0    = 0xCC
1 1 1 1 1 1 0 1    = 0xFD
1 1 1 1 1 1 1 1    = 0xFF
1 1 0 0 1 1 1 0    = 0xCE
1 1 0 0 1 1 0 1    = 0xCD
1 1 0 0 1 1 0 0    = 0xCC

....

So, as you can see you have to set bits in bytes in corresponding places and bytes into correct memory address.

Then you can color it as you need by setting color-bytes into right place in memory.

Nova days graphic memory structure is more simple and represented by 3 or 4 bytes RGB or RGBA. This leads to that, that modern PCs have to have more memory and resources and speed to provide such simplicity. 

Next step we will look into bits and bit shifting as well as bit operations - that is very important in software development.

Thank you.

1vqHSTrq1GEoEF7QsL8dhmJfRMDVxhv2y

Hi everyone,

I'm going to share two simple things you need to know to be one of the best software developers.

Really two things and they are very simple:

- You must know English language at least;

- You must understand hardware, bits, bytes and bit operations;

To be honest, one more and very useful thing is Math, thats all what you need.

Huh, seems not too much but not too little.

Lets go through all of this step by step, I will post articles here with everything you have to go through to get success.

Thank you, and be patient ;)

1vqHSTrq1GEoEF7QsL8dhmJfRMDVxhv2y