Code Optimization

Interesting things in software development and code optimization

Hardware and Bits

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.


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C#.NET - Fast Memory Copy method with x86 Assembler

Introduction

I'm Oleksandr Karpov and this is my first article here, thanks for reading it.

Here, I'm going to show and explain how to copy data really fast and how to use assembly under C# and .NET. In my case, I use it in a video creating application from images, video and sound.
Also, if you have an assembly method or function that you need to use under C#, it will show you how to do it in a quick and simple way.

Background

To understand it all, it would be great for you to know assembly language, memory alignment and some C#, Windows and .NET advanced techniques.
To be able to copy-paste data really fast, you need it to have 16 byte aligned memory address in other way it will have almost the same speed (in my case, about 1.02 time faster).

The code uses SSE instructions that are supported by processors from Pentium III+ (KNI/MMX2), AMD Athlon (AMD EMMX).

I have tested it on my Pentium Dual-Core E5800 3.2GHz with 4GB RAM in dual mode.
For me, the fast copy method is 1.5 times faster than the standard with 16 byte memory aligned and
almost the same (1.02 times faster) with non-aligned memory addresses.

To be able to allocate 16 byte aligned memory in C# under Windows, we have three ways to do it:

a) On this time it seems that Bitmap object (actually windows itself inside) allocates memory  with 16 byte aligned address, so we can use Bitmap to easy and quick aligned memory allocation;

b) As managed array by adding 8 bytes more (as windows heap is 8 byte aligned) and calculating 16 byte aligned memory point within allocated memory:

int dataLength = 4096;


// +8 bytes as windows heap is 8 byte aligned

byte[] buffer = new byte[dataLength + 8];


IntPtr addr = Marshal.UnsafeAddrOfPinnedArrayElement(buffer, 0);


//(int)(((long)addr + 15) / 16 * 16 - getting point to 16 byte aligned address

int bufferAlignedOffset = (int)(((long)addr + 15) / 16 * 16 - addr);

c) By allocating memory with VirtualAlloc API:

IntPtr addr = VirtualAlloc(IntPtr.Zero,

new UIntPtr(dataLength + 8),

AllocationTypes.Commit | AllocationTypes.Reserve,

MemoryProtections.ExecuteReadWrite);


addr = new IntPtr(((long)addr + 15) / 16 * 16);

Using the Code

This is a complete performance test that will show you performance measurements and how to use it all.

The FastMemCopy class contains all things for fast memory copy logic.

First thing you need is to create a default Windows Forms application project and put two buttons on the form and the PictureBox control as we will test it on images.

Let's declare some fields:

string bitmapPath;

Bitmap bmp, bmp2;

BitmapData bmpd, bmpd2;

byte[] buffer = null;

Now, we will create two methods to handle click events for our buttons.

For standard method:

private void btnStandard_Click(object sender, EventArgs e)

{

using (OpenFileDialog ofd = new OpenFileDialog())

{

if (ofd.ShowDialog() != System.Windows.Forms.DialogResult.OK)

return;

bitmapPath = ofd.FileName;

}


//open a selected image and create an empty image with the same size

OpenImage();


//unlock for read and write images

UnlockBitmap();

//copy data from one image to another by standard method

CopyImage();

//lock images to be able to see them

LockBitmap();

//lets see what we have

pictureBox1.Image = bmp2;

}

and for fast method:

private void btnFast_Click(object sender, EventArgs e)

{

using (OpenFileDialog ofd = new OpenFileDialog())

{

if (ofd.ShowDialog() != System.Windows.Forms.DialogResult.OK)

return;

bitmapPath = ofd.FileName;

}

//open a selected image and create an empty image with the same size

OpenImage();

//unlock for read and write images

UnlockBitmap();

//copy data from one image to another with our fast method

FastCopyImage();

//lock images to be able to see them

LockBitmap();

//lets see what we have

pictureBox1.Image = bmp2;

}

Ok, now we have buttons and event handlers so let's implement methods that will open images, lock, unlock them and standard copy method:

Open an image:

void OpenImage()

{

pictureBox1.Image = null;

buffer = null;

if (bmp != null)

{

bmp.Dispose();

bmp = null;

}

if (bmp2 != null)

{

bmp2.Dispose();

bmp2 = null;

}

GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);

bmp = (Bitmap)Bitmap.FromFile(bitmapPath);

buffer = new byte[bmp.Width * 4 * bmp.Height];

bmp2 = new Bitmap(bmp.Width, bmp.Height, bmp.Width * 4, PixelFormat.Format32bppArgb,

Marshal.UnsafeAddrOfPinnedArrayElement(buffer, 0));

}

Lock and unlock bitmaps:

void UnlockBitmap()

{

bmpd = bmp.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite,

PixelFormat.Format32bppArgb);

bmpd2 = bmp2.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadWrite,

PixelFormat.Format32bppArgb);

}

void LockBitmap()

{

bmp.UnlockBits(bmpd);

bmp2.UnlockBits(bmpd2);

}

and copy data from one image to another and show measured time:

void CopyImage()

{

//start stopwatch

Stopwatch sw = new Stopwatch();

sw.Start();

//copy-past data 10 times

for (int i = 0; i < 10; i++)

{

System.Runtime.InteropServices.Marshal.Copy(bmpd.Scan0, buffer, 0, buffer.Length);

}

//stop stopwatch

sw.Stop();

//show measured time

MessageBox.Show(sw.ElapsedTicks.ToString());

}

That's it for the standard copy-paste method. Actually, there is nothing too complex, we use well-known System.Runtime.InteropServices.Marshal.Copy method.

And one more "middle-method" for the fast copy logic:

void FastCopyImage()

{

FastMemCopy.FastMemoryCopy(bmpd.Scan0, bmpd2.Scan0, buffer.Length);

}

Now, let's implement the FastMemCopy class. Here is the declaration of the class and some types we will use inside of it:

internal static class FastMemCopy

{

[Flags]

private enum AllocationTypes : uint

{

Commit = 0x1000, Reserve = 0x2000,

Reset = 0x80000, LargePages = 0x20000000,

Physical = 0x400000, TopDown = 0x100000,

WriteWatch = 0x200000

}

[Flags]

private enum MemoryProtections : uint

{

Execute = 0x10, ExecuteRead = 0x20,

ExecuteReadWrite = 0x40, ExecuteWriteCopy = 0x80,

NoAccess = 0x01, ReadOnly = 0x02,

ReadWrite = 0x04, WriteCopy = 0x08,

GuartModifierflag = 0x100, NoCacheModifierflag = 0x200,

WriteCombineModifierflag = 0x400

}

[Flags]

private enum FreeTypes : uint

{

Decommit = 0x4000, Release = 0x8000

}

[UnmanagedFunctionPointerAttribute(CallingConvention.Cdecl)]

private unsafe delegate void FastMemCopyDelegate();

private static class NativeMethods

{

[DllImport("kernel32.dll", SetLastError = true)]

internal static extern IntPtr VirtualAlloc(

IntPtr lpAddress,

UIntPtr dwSize,

AllocationTypes flAllocationType,

MemoryProtections flProtect);

[DllImport("kernel32")]

[return: MarshalAs(UnmanagedType.Bool)]

internal static extern bool VirtualFree(

IntPtr lpAddress,

uint dwSize,

FreeTypes flFreeType);

}

Now let's declare the method itself:

public static unsafe void FastMemoryCopy(IntPtr src, IntPtr dst, int nBytes)

{

if (IntPtr.Size == 4)

{

//we are in 32 bit mode

//allocate memory for our asm method

IntPtr p = NativeMethods.VirtualAlloc(

IntPtr.Zero,

new UIntPtr((uint)x86_FastMemCopy_New.Length),

AllocationTypes.Commit | AllocationTypes.Reserve,

MemoryProtections.ExecuteReadWrite);

try

{

//copy our method bytes to allocated memory

Marshal.Copy(x86_FastMemCopy_New, 0, p, x86_FastMemCopy_New.Length);

//make a delegate to our method

FastMemCopyDelegate _fastmemcopy =

(FastMemCopyDelegate)Marshal.GetDelegateForFunctionPointer(p,

typeof(FastMemCopyDelegate));

//offset to the end of our method block

p += x86_FastMemCopy_New.Length;

//store length param

p -= 8;

Marshal.Copy(BitConverter.GetBytes((long)nBytes), 0, p, 4);

//store destination address param

p -= 8;

Marshal.Copy(BitConverter.GetBytes((long)dst), 0, p, 4);

//store source address param

p -= 8;

Marshal.Copy(BitConverter.GetBytes((long)src), 0, p, 4);

//Start stopwatch

Stopwatch sw = new Stopwatch();

sw.Start();

//copy-past all data 10 times

for (int i = 0; i < 10; i++)

_fastmemcopy();

//stop stopwatch

sw.Stop();

//get message with measured time

System.Windows.Forms.MessageBox.Show(sw.ElapsedTicks.ToString());

}

catch (Exception ex)

{

//if any exception

System.Windows.Forms.MessageBox.Show(ex.Message);

}

finally

{

//free allocated memory

NativeMethods.VirtualFree(p, (uint)(x86_FastMemCopy_New.Length),

FreeTypes.Release);

GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);

}

}

else if (IntPtr.Size == 8)

{

throw new ApplicationException("x64 is not supported yet!");

}

}

and assembly code that is represented as an array of bytes with explanation:

private static byte[] x86_FastMemCopy_New = new byte[]

{

0x90, //nop do nothing

0x60, //pushad store flag register on stack

0x95, //xchg ebp, eax eax contains memory address of our method

0x8B, 0xB5, 0x5A, 0x01, 0x00, 0x00, //mov esi,[ebp][00000015A] get source buffer address

0x89, 0xF0, //mov eax,esi

0x83, 0xE0, 0x0F, //and eax,00F will check if it is 16 byte aligned

0x8B, 0xBD, 0x62, 0x01, 0x00, 0x00, //mov edi,[ebp][000000162] get destination address

0x89, 0xFB, //mov ebx,edi

0x83, 0xE3, 0x0F, //and ebx,00F will check if it is 16 byte aligned

0x8B, 0x8D, 0x6A, 0x01, 0x00, 0x00, //mov ecx,[ebp][00000016A] get number of bytes to copy

0xC1, 0xE9, 0x07, //shr ecx,7 divide length by 128

0x85, 0xC9, //test ecx,ecx check if zero

0x0F, 0x84, 0x1C, 0x01, 0x00, 0x00, //jz 000000146 ? copy the rest

0x0F, 0x18, 0x06, //prefetchnta [esi] pre-fetch non-temporal source data for reading

0x85, 0xC0, //test eax,eax check if source address is 16 byte aligned

0x0F, 0x84, 0x8B, 0x00, 0x00, 0x00, //jz 0000000C0 ? go to copy if aligned

0x0F, 0x18, 0x86, 0x80, 0x02, 0x00, 0x00, //prefetchnta [esi][000000280] pre-fetch more source data

0x0F, 0x10, 0x06, //movups xmm0,[esi] copy 16 bytes of source data

0x0F, 0x10, 0x4E, 0x10, //movups xmm1,[esi][010] copy more 16 bytes

0x0F, 0x10, 0x56, 0x20, //movups xmm2,[esi][020] copy more

0x0F, 0x18, 0x86, 0xC0, 0x02, 0x00, 0x00, //prefetchnta [esi][0000002C0] pre-fetch more

0x0F, 0x10, 0x5E, 0x30, //movups xmm3,[esi][030]

0x0F, 0x10, 0x66, 0x40, //movups xmm4,[esi][040]

0x0F, 0x10, 0x6E, 0x50, //movups xmm5,[esi][050]

0x0F, 0x10, 0x76, 0x60, //movups xmm6,[esi][060]

0x0F, 0x10, 0x7E, 0x70, //movups xmm7,[esi][070] we've copied 128 bytes of source data

0x85, 0xDB, //test ebx,ebx check if destination address is 16 byte aligned

0x74, 0x21, //jz 000000087 ? go to past if aligned

0x0F, 0x11, 0x07, //movups [edi],xmm0 past first 16 bytes to non-aligned destination address

0x0F, 0x11, 0x4F, 0x10, //movups [edi][010],xmm1 past more

0x0F, 0x11, 0x57, 0x20, //movups [edi][020],xmm2

0x0F, 0x11, 0x5F, 0x30, //movups [edi][030],xmm3

0x0F, 0x11, 0x67, 0x40, //movups [edi][040],xmm4

0x0F, 0x11, 0x6F, 0x50, //movups [edi][050],xmm5

0x0F, 0x11, 0x77, 0x60, //movups [edi][060],xmm6

0x0F, 0x11, 0x7F, 0x70, //movups [edi][070],xmm7 we've pasted 128 bytes of source data

0xEB, 0x1F, //jmps 0000000A6 ? continue

0x0F, 0x2B, 0x07, //movntps [edi],xmm0 past first 16 bytes to aligned destination address

0x0F, 0x2B, 0x4F, 0x10, //movntps [edi][010],xmm1 past more

0x0F, 0x2B, 0x57, 0x20, //movntps [edi][020],xmm2

0x0F, 0x2B, 0x5F, 0x30, //movntps [edi][030],xmm3

0x0F, 0x2B, 0x67, 0x40, //movntps [edi][040],xmm4

0x0F, 0x2B, 0x6F, 0x50, //movntps [edi][050],xmm5

0x0F, 0x2B, 0x77, 0x60, //movntps [edi][060],xmm6

0x0F, 0x2B, 0x7F, 0x70, //movntps [edi][070],xmm7 we've pasted 128 bytes of source data

0x81, 0xC6, 0x80, 0x00, 0x00, 0x00, //add esi,000000080 increment source address by 128

0x81, 0xC7, 0x80, 0x00, 0x00, 0x00, //add edi,000000080 increment destination address by 128

0x83, 0xE9, 0x01, //sub ecx,1 decrement counter

0x0F, 0x85, 0x7A, 0xFF, 0xFF, 0xFF, //jnz 000000035 ? continue if not zero

0xE9, 0x86, 0x00, 0x00, 0x00, //jmp 000000146 ? go to copy the rest of data

0x0F, 0x18, 0x86, 0x80, 0x02, 0x00, 0x00, //prefetchnta [esi][000000280] pre-fetch source data

0x0F, 0x28, 0x06, //movaps xmm0,[esi] copy 128 bytes from aligned source address

0x0F, 0x28, 0x4E, 0x10, //movaps xmm1,[esi][010] copy more

0x0F, 0x28, 0x56, 0x20, //movaps xmm2,[esi][020]

0x0F, 0x18, 0x86, 0xC0, 0x02, 0x00, 0x00, //prefetchnta [esi][0000002C0] pre-fetch more data

0x0F, 0x28, 0x5E, 0x30, //movaps xmm3,[esi][030]

0x0F, 0x28, 0x66, 0x40, //movaps xmm4,[esi][040]

0x0F, 0x28, 0x6E, 0x50, //movaps xmm5,[esi][050]

0x0F, 0x28, 0x76, 0x60, //movaps xmm6,[esi][060]

0x0F, 0x28, 0x7E, 0x70, //movaps xmm7,[esi][070] we've copied 128 bytes of source data

0x85, 0xDB, //test ebx,ebx check if destination address is 16 byte aligned

0x74, 0x21, //jz 000000112 ? go to past if aligned

0x0F, 0x11, 0x07, //movups [edi],xmm0 past 16 bytes to non-aligned destination address

0x0F, 0x11, 0x4F, 0x10, //movups [edi][010],xmm1 past more

0x0F, 0x11, 0x57, 0x20, //movups [edi][020],xmm2

0x0F, 0x11, 0x5F, 0x30, //movups [edi][030],xmm3

0x0F, 0x11, 0x67, 0x40, //movups [edi][040],xmm4

0x0F, 0x11, 0x6F, 0x50, //movups [edi][050],xmm5

0x0F, 0x11, 0x77, 0x60, //movups [edi][060],xmm6

0x0F, 0x11, 0x7F, 0x70, //movups [edi][070],xmm7 we've pasted 128 bytes of data

0xEB, 0x1F, //jmps 000000131 ? continue copy-past

0x0F, 0x2B, 0x07, //movntps [edi],xmm0 past 16 bytes to aligned destination address

0x0F, 0x2B, 0x4F, 0x10, //movntps [edi][010],xmm1 past more

0x0F, 0x2B, 0x57, 0x20, //movntps [edi][020],xmm2

0x0F, 0x2B, 0x5F, 0x30, //movntps [edi][030],xmm3

0x0F, 0x2B, 0x67, 0x40, //movntps [edi][040],xmm4

0x0F, 0x2B, 0x6F, 0x50, //movntps [edi][050],xmm5

0x0F, 0x2B, 0x77, 0x60, //movntps [edi][060],xmm6

0x0F, 0x2B, 0x7F, 0x70, //movntps [edi][070],xmm7 we've pasted 128 bytes of data

0x81, 0xC6, 0x80, 0x00, 0x00, 0x00, //add esi,000000080 increment source address by 128

0x81, 0xC7, 0x80, 0x00, 0x00, 0x00, //add edi,000000080 increment destination address by 128

0x83, 0xE9, 0x01, //sub ecx,1 decrement counter

0x0F, 0x85, 0x7A, 0xFF, 0xFF, 0xFF, //jnz 0000000C0 ? continue copy-past if non-zero

0x8B, 0x8D, 0x6A, 0x01, 0x00, 0x00, //mov ecx,[ebp][00000016A] get number of bytes to copy

0x83, 0xE1, 0x7F, //and ecx,07F get rest number of bytes

0x85, 0xC9, //test ecx,ecx check if there are bytes

0x74, 0x02, //jz 000000155 ? exit if there are no more bytes

0xF3, 0xA4, //rep movsb copy rest of bytes

0x0F, 0xAE, 0xF8, //sfence performs a serializing operation on all store-to-memory instructions

0x61, //popad restore flag register

0xC3, //retn return from our method to C#

0x00, 0x00, 0x00, 0x00, //source buffer address

0x00, 0x00, 0x00, 0x00,

0x00, 0x00, 0x00, 0x00, //destination buffer address

0x00, 0x00, 0x00, 0x00,

0x00, 0x00, 0x00, 0x00, //number of bytes to copy-past

0x00, 0x00, 0x00, 0x00

};

We will call this assembly method via delegate we have created earlier.

This method works in 32 bit mode for now and I will implement the 64 bit mode later.
I will add source code if anyone is interested in it (almost all code is there in the article).

Pay attention, the assembly code throws an exception if it is run under Visual Studio, and I still don't understand why.

Points of Interest

During implementation and testing this method, I have found that prefetchnta command is not very clear described even by the Intel specification, so I did try to figure out it myself and via Google.
Also, pay attention to movntps and movaps instructions as they work with 16-byte memory aligned addresses only.

History

  • Bitmap and 16 byte memory alignment
  • Source code and memory alignment samples were added
  • First version - 06/23/2015
FastMemoryCopy_src.zip (14.4KB)

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Do you want to be best software developer?

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