I need your help with calculating checksum in C#. Code below is for application writen in C++. App is receiving packets from UDP. This is part of code where is receive and checksum calculation.
struct OPtoLSs {BlockReceivedS hdr; char data[0x100];}; //struct for received data
OPtoLSs mCKr;
#define hdrR mCKr.hdr.OPhdr
#define dataR mCKr.data
int const retHdr = recvfrom(sock, (char*)&hdrR, sizeof(hdrR), 0, (sockaddr*)(&from), &len);
int const retDat = recvfrom(sock, (char*)&dataR, hdrR.Length, 0, (sockaddr*)(&from), &len);
for(unsigned _int16 *p = (unsigned _int16*)&mCKr; p < (unsigned _int16*)&mCKr + ((retHdr+retDat)/2); p++)
{
ChkSum=(_int16)((*p+ChkSum)&0xffff);
}
assert_hard(ChkSum==0xffff);
I need to get right calculation for checksum in C#. I used code below, but when I send any msg from C# side to C++ side, it throws this error. Please can somebody help with this calculation in C# ? Thanks for all your responses.
// mCKr.hdr.OPhdr equivalent
[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi, Size = 12)]
public struct OPpacketHdrS
{
public UInt32 packetMark;
public UInt32 OPpacketID;
public UInt16 ChKSum
{
get
{
UInt16 accumulator = 0;
unsafe
{
fixed (OPpacketHdrS* x = &this)
{
for (UInt16* p = (UInt16*)x; p < x + 1; ++p)
{
accumulator += *p;
}
}
}
return accumulator;
}
}
public UInt16 Length;
}
// mCKr.data equivalent
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Size = 20)]
public struct CommandKeyS
{
public OPpacketHdrS OPhdr;
public mHdr Hdr; // Hdr.ID=CommandKeyR
[MarshalAs(UnmanagedType.U2)]
public UInt16 cmdKey, unused;
}
The server calculates the checksum only of the half of the received header and data. Sent checksum should lead to calculated checksum become 0xffff.
I assume you are sending to the server CommandKeyS structure and it's size is constant. I assume ChkSum on the server is of type _int16 and initialized to 0.
I dont know C#, so replaced parts with C++ code hoping it's not too different. You can remove get function of ChKSum field and before sending the data call this function to initialize the checksum:
CalcChecksum( CommandKeyS* sentData )
{
//At this point all fields in sentData, except of OPhdr.ChKSum are properly initialized.
UInt16 accumulator = 0;
unsafe
{
//Calculate checksum of the half of the data without using ChKSum.
UInt32 chkSummedLen = sizeof( CommandKeyS )/2;
UInt8* chkSummedEnd = ((UInt8*)sentData) + chkSummedLen;
sentData->OPhdr.ChKSum = 0;
for (UInt16* p = (UInt16*)sentData; p < chkSummedEnd; ++p)
{
accumulator += *p;
}
//Calculate ChKSum to make the calculated checksum be equal to 0xffff.
sentData->OPhdr.ChKSum = 0xffff - accumulator;
}
}
The way of calculating checksums your server uses is not obvious and possibly not correct, since the bottom part of the data is not checksummed.
I am trying to use a DLL written in C in a C# application. I've created a simplified example that replicates the issue I am having.
The C code below creates an array of struct data's and assigns the array pointer to the array parameter passed to the get_data() function. The C# code is supposed to be the boilerplate code needed for marshalling the struct to be used in C#, but is presenting issues for me.
C code
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
struct data {
int32_t value;
union {
struct person {
uint8_t first[10];
uint8_t last[10];
} person;
struct number {
int32_t imaginary;
int32_t real;
} number;
} type;
};
int get_data(int count, struct data ***array)
{
int i;
/* allocate pointers */
*array = calloc(count, sizeof(struct data*));
if (*array == NULL)
return 1;
for (i = 0; i < count; i++) {
/* allocate data struct */
struct data *data = calloc(1, sizeof(struct data));
if (data == NULL)
return 2;
if ((i % 2) == 0) {
/* if even, its human */
data->value = i;
memcpy(data->type.person.first, "john", 4);
memcpy(data->type.person.last, "doe", 3);
} else {
/* if odd its a number */
data->value = i;
data->type.number.imaginary = -1;
data->type.number.real = i + 1;
}
(*array)[i] = data;
}
return 0;
}
C# code
[DllImport("libdata.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern Int32 get_data(Int32 count, ref IntPtr array);
[StructLayout(LayoutKind.Sequential)]
public struct Person
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
public String first;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 10)]
public String last;
}
[StructLayout(LayoutKind.Sequential)]
public struct Number
{
public Int32 imaginary;
public Int32 real;
}
[StructLayout(LayoutKind.Explicit)]
public struct TypeUnion
{
[FieldOffset(0)]
public Person person;
[FieldOffset(0)]
public Number number;
}
[StructLayout(LayoutKind.Sequential)]
public struct Data
{
public Int32 value;
public TypeUnion type;
}
Right now when I run my test program I get an exception:
System.TypeLoadException was unhandled
Message=Could not load type 'WpfRibbonApplication1.TypeUnion' from assembly 'WpfRibbonApplication1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' because it contains an object field at offset 0 that is incorrectly aligned or overlapped by a non-object field.
I have tried several different ways of marshalling the Person strings, but get the exception whichever way I try (using this as reference). Am I missing something obvious? Could I get some help to properly read the array created in the C function within my C# application?
Edit (per David Heffernan's comment)
IntPtr arrayPtr = new IntPtr();
int count = 4;
int ret = LibData.get_data(count, ref arrayPtr);
Console.WriteLine("ret=" + ret);
for (int i = 0; i < count; i++)
{
IntPtr dataPtr = (IntPtr)Marshal.ReadIntPtr(arrayPtr) + (i * Marshal.SizeOf(typeof(IntPtr)));
Data data = (Data)Marshal.PtrToStructure(dataPtr, typeof(Data));
Console.WriteLine("value=" + data.value);
if ((i % 2) == 0)
{
// even is human
Console.WriteLine("first=" + data.type.first);
Console.WriteLine("last=" + data.type.last);
}
else
{
// odd is number
Console.WriteLine("imaginary=" + data.type.imaginary);
Console.WriteLine("real=" + data.type.real);
}
Console.WriteLine("");
}
The error message is telling you that you cannot overlay an object field with a non-object field. You are overlaying a string with an int.
There's no way you are going to get around that using FieldOffset to replicate the native union. As I see it you have two main options:
Stop using a union and include both Person and Number structs in the Data struct.
Continue using a union, but marshal it yourself. Use the Marshal class to read the data in the struct. For example, you'd use Marshal.ReadInt32 to read the integers, Marshal.Copy to read the character arrays and so on.
Question
I'm porting a C application into C#. The C app calls lots of functions from a 3rd-party DLL, so I wrote P/Invoke wrappers for these functions in C#. Some of these C functions allocate data which I have to use in the C# app, so I used IntPtr's, Marshal.PtrToStructure and Marshal.Copy to copy the native data (arrays and structures) into managed variables.
Unfortunately, the C# app proved to be much slower than the C version. A quick performance analysis showed that the above mentioned marshaling-based data copying is the bottleneck. I'm considering to speed up the C# code by rewriting it to use pointers instead. Since I don't have experience with unsafe code and pointers in C#, I need expert opinion regarding the following questions:
What are the drawbacks of using unsafe code and pointers instead of IntPtr and Marshaling? For example, is it more unsafe (pun intended) in any way? People seem to prefer marshaling, but I don't know why.
Is using pointers for P/Invoking really faster than using marshaling? How much speedup can be expected approximately? I couldn't find any benchmark tests for this.
Example code
To make the situation more clear, I hacked together a small example code (the real code is much more complex). I hope this example shows what I mean when I'm talking about "unsafe code and pointers" vs. "IntPtr and Marshal".
C library (DLL)
MyLib.h
#ifndef _MY_LIB_H_
#define _MY_LIB_H_
struct MyData
{
int length;
unsigned char* bytes;
};
__declspec(dllexport) void CreateMyData(struct MyData** myData, int length);
__declspec(dllexport) void DestroyMyData(struct MyData* myData);
#endif // _MY_LIB_H_
MyLib.c
#include <stdlib.h>
#include "MyLib.h"
void CreateMyData(struct MyData** myData, int length)
{
int i;
*myData = (struct MyData*)malloc(sizeof(struct MyData));
if (*myData != NULL)
{
(*myData)->length = length;
(*myData)->bytes = (unsigned char*)malloc(length * sizeof(char));
if ((*myData)->bytes != NULL)
for (i = 0; i < length; ++i)
(*myData)->bytes[i] = (unsigned char)(i % 256);
}
}
void DestroyMyData(struct MyData* myData)
{
if (myData != NULL)
{
if (myData->bytes != NULL)
free(myData->bytes);
free(myData);
}
}
C application
Main.c
#include <stdio.h>
#include "MyLib.h"
void main()
{
struct MyData* myData = NULL;
int length = 100 * 1024 * 1024;
printf("=== C++ test ===\n");
CreateMyData(&myData, length);
if (myData != NULL)
{
printf("Length: %d\n", myData->length);
if (myData->bytes != NULL)
printf("First: %d, last: %d\n", myData->bytes[0], myData->bytes[myData->length - 1]);
else
printf("myData->bytes is NULL");
}
else
printf("myData is NULL\n");
DestroyMyData(myData);
getchar();
}
C# application, which uses IntPtr and Marshal
Program.cs
using System;
using System.Runtime.InteropServices;
public static class Program
{
[StructLayout(LayoutKind.Sequential)]
private struct MyData
{
public int Length;
public IntPtr Bytes;
}
[DllImport("MyLib.dll")]
private static extern void CreateMyData(out IntPtr myData, int length);
[DllImport("MyLib.dll")]
private static extern void DestroyMyData(IntPtr myData);
public static void Main()
{
Console.WriteLine("=== C# test, using IntPtr and Marshal ===");
int length = 100 * 1024 * 1024;
IntPtr myData1;
CreateMyData(out myData1, length);
if (myData1 != IntPtr.Zero)
{
MyData myData2 = (MyData)Marshal.PtrToStructure(myData1, typeof(MyData));
Console.WriteLine("Length: {0}", myData2.Length);
if (myData2.Bytes != IntPtr.Zero)
{
byte[] bytes = new byte[myData2.Length];
Marshal.Copy(myData2.Bytes, bytes, 0, myData2.Length);
Console.WriteLine("First: {0}, last: {1}", bytes[0], bytes[myData2.Length - 1]);
}
else
Console.WriteLine("myData.Bytes is IntPtr.Zero");
}
else
Console.WriteLine("myData is IntPtr.Zero");
DestroyMyData(myData1);
Console.ReadKey(true);
}
}
C# application, which uses unsafe code and pointers
Program.cs
using System;
using System.Runtime.InteropServices;
public static class Program
{
[StructLayout(LayoutKind.Sequential)]
private unsafe struct MyData
{
public int Length;
public byte* Bytes;
}
[DllImport("MyLib.dll")]
private unsafe static extern void CreateMyData(out MyData* myData, int length);
[DllImport("MyLib.dll")]
private unsafe static extern void DestroyMyData(MyData* myData);
public unsafe static void Main()
{
Console.WriteLine("=== C# test, using unsafe code ===");
int length = 100 * 1024 * 1024;
MyData* myData;
CreateMyData(out myData, length);
if (myData != null)
{
Console.WriteLine("Length: {0}", myData->Length);
if (myData->Bytes != null)
Console.WriteLine("First: {0}, last: {1}", myData->Bytes[0], myData->Bytes[myData->Length - 1]);
else
Console.WriteLine("myData.Bytes is null");
}
else
Console.WriteLine("myData is null");
DestroyMyData(myData);
Console.ReadKey(true);
}
}
It's a little old thread, but I recently made excessive performance tests with marshaling in C#. I need to unmarshal lots of data from a serial port over many days. It was important to me to have no memory leaks (because the smallest leak will get significant after a couple of million calls) and I also made a lot of statistical performance (time used) tests with very big structs (>10kb) just for the sake of it (an no, you should never have a 10kb struct :-) )
I tested the following three unmarshalling strategies (I also tested the marshalling). In nearly all cases the first one (MarshalMatters) outperformed the other two.
Marshal.Copy was always slowest by far, the other two were mostly very close together in the race.
Using unsafe code can pose a significant security risk.
First:
public class MarshalMatters
{
public static T ReadUsingMarshalUnsafe<T>(byte[] data) where T : struct
{
unsafe
{
fixed (byte* p = &data[0])
{
return (T)Marshal.PtrToStructure(new IntPtr(p), typeof(T));
}
}
}
public unsafe static byte[] WriteUsingMarshalUnsafe<selectedT>(selectedT structure) where selectedT : struct
{
byte[] byteArray = new byte[Marshal.SizeOf(structure)];
fixed (byte* byteArrayPtr = byteArray)
{
Marshal.StructureToPtr(structure, (IntPtr)byteArrayPtr, true);
}
return byteArray;
}
}
Second:
public class Adam_Robinson
{
private static T BytesToStruct<T>(byte[] rawData) where T : struct
{
T result = default(T);
GCHandle handle = GCHandle.Alloc(rawData, GCHandleType.Pinned);
try
{
IntPtr rawDataPtr = handle.AddrOfPinnedObject();
result = (T)Marshal.PtrToStructure(rawDataPtr, typeof(T));
}
finally
{
handle.Free();
}
return result;
}
/// <summary>
/// no Copy. no unsafe. Gets a GCHandle to the memory via Alloc
/// </summary>
/// <typeparam name="selectedT"></typeparam>
/// <param name="structure"></param>
/// <returns></returns>
public static byte[] StructToBytes<T>(T structure) where T : struct
{
int size = Marshal.SizeOf(structure);
byte[] rawData = new byte[size];
GCHandle handle = GCHandle.Alloc(rawData, GCHandleType.Pinned);
try
{
IntPtr rawDataPtr = handle.AddrOfPinnedObject();
Marshal.StructureToPtr(structure, rawDataPtr, false);
}
finally
{
handle.Free();
}
return rawData;
}
}
Third:
/// <summary>
/// http://stackoverflow.com/questions/2623761/marshal-ptrtostructure-and-back-again-and-generic-solution-for-endianness-swap
/// </summary>
public class DanB
{
/// <summary>
/// uses Marshal.Copy! Not run in unsafe. Uses AllocHGlobal to get new memory and copies.
/// </summary>
public static byte[] GetBytes<T>(T structure) where T : struct
{
var size = Marshal.SizeOf(structure); //or Marshal.SizeOf<selectedT>(); in .net 4.5.1
byte[] rawData = new byte[size];
IntPtr ptr = Marshal.AllocHGlobal(size);
Marshal.StructureToPtr(structure, ptr, true);
Marshal.Copy(ptr, rawData, 0, size);
Marshal.FreeHGlobal(ptr);
return rawData;
}
public static T FromBytes<T>(byte[] bytes) where T : struct
{
var structure = new T();
int size = Marshal.SizeOf(structure); //or Marshal.SizeOf<selectedT>(); in .net 4.5.1
IntPtr ptr = Marshal.AllocHGlobal(size);
Marshal.Copy(bytes, 0, ptr, size);
structure = (T)Marshal.PtrToStructure(ptr, structure.GetType());
Marshal.FreeHGlobal(ptr);
return structure;
}
}
Considerations in Interoperability explains why and when Marshaling is required and at what cost. Quote:
Marshaling occurs when a caller and a callee cannot operate on the same instance of data.
repeated marshaling can negatively affect the performance of your application.
Therefore, answering your question if
... using pointers for P/Invoking really faster than using marshaling ...
first ask yourself a question if the managed code is able to operate on the unmanaged method return value instance. If the answer is yes then Marshaling and the associated performance cost is not required.
The approximate time saving would be O(n) function where n of the size of the marshalled instance.
In addition, not keeping both managed and unmanaged blocks of data in memory at the same time for the duration of the method (in "IntPtr and Marshal" example) eliminates additional overhead and the memory pressure.
What are the drawbacks of using unsafe code and pointers ...
The drawback is the risk associated with accessing the memory directly through pointers. There is nothing less safe to it than using pointers in C or C++. Use it if needed and makes sense. More details are here.
There is one "safety" concern with the presented examples: releasing of allocated unmanaged memory is not guaranteed after the managed code errors. The best practice is to
CreateMyData(out myData1, length);
if(myData1!=IntPtr.Zero) {
try {
// -> use myData1
...
// <-
}
finally {
DestroyMyData(myData1);
}
}
For anyone still reading,
Something I don't think I saw in any of the answers, - unsafe code does present something of a security risk. It's not a huge risk, it would be something quite challenging to exploit. However, if like me you work in a PCI compliant organization, unsafe code is disallowed by policy for this reason.
Managed code is normally very secure because the CLR takes care of memory location and allocation, preventing you from accessing or writing any memory you're not supposed to.
When you use the unsafe keyword and compile with '/unsafe' and use pointers, you bypass these checks and create the potential for someone to use your application to gain some level of unauthorized access to the machine it is running on. Using something like a buffer-overrun attack, your code could be tricked into writing instructions into an area of memory that might then be accessed by the program counter (i.e. code injection), or just crash the machine.
Many years ago, SQL server actually fell prey to malicious code delivered in a TDS packet that was far longer than it was supposed to be. The method reading the packet didn't check the length and continued to write the contents past the reserved address space. The extra length and content were carefully crafted such that it wrote an entire program into memory - at the address of the next method.
The attacker then had their own code being executed by the SQL server within a context that had the highest level of access. It didn't even need to break the encryption as the vulnerability was below this point in the transport layer stack.
Just wanted to add my experience to this old thread:
We used Marshaling in sound recording software - we received real time sound data from mixer into native buffers and marshaled it to byte[]. That was real performance killer. We were forced to move to unsafe structs as the only way to complete the task.
In case you don't have large native structs and don't mind that all data is filled twice - Marshaling is more elegant and much, much safer approach.
Two answers,
Unsafe code means it is not managed by the CLR. You need to take care of resources it uses.
You cannot scale the performance because there are so many factors effecting it. But definitely using pointers will be much faster.
Because you stated that your code calls to 3rd-party DLL, I think the unsafe code is more suited in you scenario. You ran into a particular situation of wapping variable-length array in a struct; I know, I know this kind of usage occurs all the time, but it's not always the case after all. You might want to have a look of some questions about this, for example:
How do I marshal a struct that contains a variable-sized array to C#?
If .. I say if .. you can modify the third party libraries a bit for this particular case, then you might consider the following usage:
using System.Runtime.InteropServices;
public static class Program { /*
[StructLayout(LayoutKind.Sequential)]
private struct MyData {
public int Length;
public byte[] Bytes;
} */
[DllImport("MyLib.dll")]
// __declspec(dllexport) void WINAPI CreateMyDataAlt(BYTE bytes[], int length);
private static extern void CreateMyDataAlt(byte[] myData, ref int length);
/*
[DllImport("MyLib.dll")]
private static extern void DestroyMyData(byte[] myData); */
public static void Main() {
Console.WriteLine("=== C# test, using IntPtr and Marshal ===");
int length = 100*1024*1024;
var myData1 = new byte[length];
CreateMyDataAlt(myData1, ref length);
if(0!=length) {
// MyData myData2 = (MyData)Marshal.PtrToStructure(myData1, typeof(MyData));
Console.WriteLine("Length: {0}", length);
/*
if(myData2.Bytes!=IntPtr.Zero) {
byte[] bytes = new byte[myData2.Length];
Marshal.Copy(myData2.Bytes, bytes, 0, myData2.Length); */
Console.WriteLine("First: {0}, last: {1}", myData1[0], myData1[length-1]); /*
}
else {
Console.WriteLine("myData.Bytes is IntPtr.Zero");
} */
}
else {
Console.WriteLine("myData is empty");
}
// DestroyMyData(myData1);
Console.ReadKey(true);
}
}
As you can see much of your original marshalling code is commented out, and declared a CreateMyDataAlt(byte[], ref int) for a coresponding modified external unmanaged function CreateMyDataAlt(BYTE [], int). Some of the data copy and pointer check turns to be unnecessary, that says, the code can be even simpler and probably runs faster.
So, what's so different with the modification? The byte array is now marshalled directly without warpping in a struct and passed to the unmanaged side. You don't allocate the memory within the unmanaged code, rather, just filling data to it(implementation details omitted); and after the call, the data needed is provided to the managed side. If you want to present that the data is not filled and should not be used, you can simply set length to zero to tell the managed side. Because the byte array is allocated within the managed side, it'll be collected sometime, you don't have to take care of that.
I had the same question today and I was looking for some concrete measurement values, but I couldn't find any. So I wrote my own tests.
The test is copying pixel data of a 10k x 10k RGB image. The image data is 300 MB (3*10^9 bytes). Some methods copy this data 10 times, others are faster and therefore copy it 100 times. The used copying methods include
array access via byte pointer
Marshal.Copy(): a) 1 * 300 MB, b) 1e9 * 3 bytes
Buffer.BlockCopy(): a) 1 * 300 MB, b) 1e9 * 3 bytes
Test environment:
CPU: Intel Core i7-3630QM # 2.40 GHz
OS: Win 7 Pro x64 SP1
Visual Studio 2015.3, code is C++/CLI, targeted .net version is 4.5.2, compiled for Debug.
Test results:
The CPU load is 100% for 1 core at all methods (equals 12.5% total CPU load).
Comparison of speed and execution time:
method speed exec.time
Marshal.Copy (1*300MB) 100 % 100%
Buffer.BlockCopy (1*300MB) 98 % 102%
Pointer 4.4 % 2280%
Buffer.BlockCopy (1e9*3B) 1.4 % 7120%
Marshal.Copy (1e9*3B) 0.95% 10600%
Execution times and calculated average throughput written as comments in the code below.
//------------------------------------------------------------------------------
static void CopyIntoBitmap_Pointer (array<unsigned char>^ i_aui8ImageData,
BitmapData^ i_ptrBitmap,
int i_iBytesPerPixel)
{
char* scan0 = (char*)(i_ptrBitmap->Scan0.ToPointer ());
int ixCnt = 0;
for (int ixRow = 0; ixRow < i_ptrBitmap->Height; ixRow++)
{
for (int ixCol = 0; ixCol < i_ptrBitmap->Width; ixCol++)
{
char* pPixel = scan0 + ixRow * i_ptrBitmap->Stride + ixCol * 3;
pPixel[0] = i_aui8ImageData[ixCnt++];
pPixel[1] = i_aui8ImageData[ixCnt++];
pPixel[2] = i_aui8ImageData[ixCnt++];
}
}
}
//------------------------------------------------------------------------------
static void CopyIntoBitmap_MarshallLarge (array<unsigned char>^ i_aui8ImageData,
BitmapData^ i_ptrBitmap)
{
IntPtr ptrScan0 = i_ptrBitmap->Scan0;
Marshal::Copy (i_aui8ImageData, 0, ptrScan0, i_aui8ImageData->Length);
}
//------------------------------------------------------------------------------
static void CopyIntoBitmap_MarshalSmall (array<unsigned char>^ i_aui8ImageData,
BitmapData^ i_ptrBitmap,
int i_iBytesPerPixel)
{
int ixCnt = 0;
for (int ixRow = 0; ixRow < i_ptrBitmap->Height; ixRow++)
{
for (int ixCol = 0; ixCol < i_ptrBitmap->Width; ixCol++)
{
IntPtr ptrScan0 = IntPtr::Add (i_ptrBitmap->Scan0, i_iBytesPerPixel);
Marshal::Copy (i_aui8ImageData, ixCnt, ptrScan0, i_iBytesPerPixel);
ixCnt += i_iBytesPerPixel;
}
}
}
//------------------------------------------------------------------------------
void main ()
{
int iWidth = 10000;
int iHeight = 10000;
int iBytesPerPixel = 3;
Bitmap^ oBitmap = gcnew Bitmap (iWidth, iHeight, PixelFormat::Format24bppRgb);
BitmapData^ oBitmapData = oBitmap->LockBits (Rectangle (0, 0, iWidth, iHeight), ImageLockMode::WriteOnly, oBitmap->PixelFormat);
array<unsigned char>^ aui8ImageData = gcnew array<unsigned char> (iWidth * iHeight * iBytesPerPixel);
int ixCnt = 0;
for (int ixRow = 0; ixRow < iHeight; ixRow++)
{
for (int ixCol = 0; ixCol < iWidth; ixCol++)
{
aui8ImageData[ixCnt++] = ixRow * 250 / iHeight;
aui8ImageData[ixCnt++] = ixCol * 250 / iWidth;
aui8ImageData[ixCnt++] = ixCol;
}
}
//========== Pointer ==========
// ~ 8.97 sec for 10k * 10k * 3 * 10 exec, ~ 334 MB/s
int iExec = 10;
DateTime dtStart = DateTime::Now;
for (int ixExec = 0; ixExec < iExec; ixExec++)
{
CopyIntoBitmap_Pointer (aui8ImageData, oBitmapData, iBytesPerPixel);
}
TimeSpan tsDuration = DateTime::Now - dtStart;
Console::WriteLine (tsDuration + " " + ((double)aui8ImageData->Length * iExec / tsDuration.TotalSeconds / 1e6));
//========== Marshal.Copy, 1 large block ==========
// 3.94 sec for 10k * 10k * 3 * 100 exec, ~ 7617 MB/s
iExec = 100;
dtStart = DateTime::Now;
for (int ixExec = 0; ixExec < iExec; ixExec++)
{
CopyIntoBitmap_MarshallLarge (aui8ImageData, oBitmapData);
}
tsDuration = DateTime::Now - dtStart;
Console::WriteLine (tsDuration + " " + ((double)aui8ImageData->Length * iExec / tsDuration.TotalSeconds / 1e6));
//========== Marshal.Copy, many small 3-byte blocks ==========
// 41.7 sec for 10k * 10k * 3 * 10 exec, ~ 72 MB/s
iExec = 10;
dtStart = DateTime::Now;
for (int ixExec = 0; ixExec < iExec; ixExec++)
{
CopyIntoBitmap_MarshalSmall (aui8ImageData, oBitmapData, iBytesPerPixel);
}
tsDuration = DateTime::Now - dtStart;
Console::WriteLine (tsDuration + " " + ((double)aui8ImageData->Length * iExec / tsDuration.TotalSeconds / 1e6));
//========== Buffer.BlockCopy, 1 large block ==========
// 4.02 sec for 10k * 10k * 3 * 100 exec, ~ 7467 MB/s
iExec = 100;
array<unsigned char>^ aui8Buffer = gcnew array<unsigned char> (aui8ImageData->Length);
dtStart = DateTime::Now;
for (int ixExec = 0; ixExec < iExec; ixExec++)
{
Buffer::BlockCopy (aui8ImageData, 0, aui8Buffer, 0, aui8ImageData->Length);
}
tsDuration = DateTime::Now - dtStart;
Console::WriteLine (tsDuration + " " + ((double)aui8ImageData->Length * iExec / tsDuration.TotalSeconds / 1e6));
//========== Buffer.BlockCopy, many small 3-byte blocks ==========
// 28.0 sec for 10k * 10k * 3 * 10 exec, ~ 107 MB/s
iExec = 10;
dtStart = DateTime::Now;
for (int ixExec = 0; ixExec < iExec; ixExec++)
{
int ixCnt = 0;
for (int ixRow = 0; ixRow < iHeight; ixRow++)
{
for (int ixCol = 0; ixCol < iWidth; ixCol++)
{
Buffer::BlockCopy (aui8ImageData, ixCnt, aui8Buffer, ixCnt, iBytesPerPixel);
ixCnt += iBytesPerPixel;
}
}
}
tsDuration = DateTime::Now - dtStart;
Console::WriteLine (tsDuration + " " + ((double)aui8ImageData->Length * iExec / tsDuration.TotalSeconds / 1e6));
oBitmap->UnlockBits (oBitmapData);
oBitmap->Save ("d:\\temp\\bitmap.bmp", ImageFormat::Bmp);
}
related information:
Why is memcpy() and memmove() faster than pointer increments?
Array.Copy vs Buffer.BlockCopy, Answer https://stackoverflow.com/a/33865267
https://github.com/dotnet/coreclr/issues/2430 "Array.Copy & Buffer.BlockCopy x2 to x3 slower < 1kB"
https://github.com/dotnet/coreclr/blob/master/src/vm/comutilnative.cpp, Line 718 at the time of writing: Buffer.BlockCopy() uses memmove
So this is might become overly complex to explain, but I'll try to keep it simple yet informative. my program, which is written in C#.net, monitors a microphone for 2 seconds and returns the Maximum value from a sample. I'm not super well versed with how sound and so forth is generated from winmm.dll, but my program is based loosely on NAudio and another project from CodeProject to visualize a wave. The wave format that I am using is this
//WaveIn.cs
private WaveFormat Format= new WaveFormat(8000, 16,1);
//waveFormat.cs
[StructLayout(LayoutKind.Sequential)]
public class WaveFormat
{
public short wFormatTag;
public short nChannels;
public int nSamplesPerSec;
public int nAvgBytesPerSec;
public short nBlockAlign;
public short wBitsPerSample;
public short cbSize;
public WaveFormat(int rate, int bits, short channels)
{
wFormatTag = (short)WaveFormats.Pcm;
nChannels = channels;
nSamplesPerSec = rate;
wBitsPerSample = (short)bits;
cbSize = 0;
nBlockAlign = (short)(nChannels * (wBitsPerSample / 8));
nAvgBytesPerSec = nSamplesPerSec * nBlockAlign;
}
(I think i may have just found my problem, by posting this but i'm still going to ask)
so then i setup a event for max sound level in my wavein file. If i understand the source code correctly it fires when the buffer is full. here is that code
private void CallBack(IntPtr waveInHandle, WaveMessage message, int userData, ref WaveHeader waveHeader, IntPtr reserved)
{
if (message == WaveMessage.WIM_DATA)
{
GCHandle hBuffer = (GCHandle)waveHeader.dwUser;
WaveInBuffer buffer = (WaveInBuffer)hBuffer.Target;
Exception exception = null;
if (DataAvailable != null)
{
DataAvailable(buffer.Data, buffer.BytesRecorded);
}
if (MaxSoundLevel != null) //FOLLOW THIS ONE
{
byte[] waveStream = new byte[buffer.BytesRecorded];
Marshal.Copy(buffer.Data, waveStream, 0, buffer.BytesRecorded);
MaxSoundLevel(GetMaxSound(GetWaveChannels(waveStream)));
}
if (recording)
{
try
{
buffer.Reuse();
}
catch (Exception e)
{
recording = false;
exception = e;
}
}
}
}
private short[] GetWaveChannels(byte[] waveStream)
{
short[] monoWave = new short[waveStream.Length/2];
int h=0;
for (int i = 0 ; i < waveStream.Length; i += 2)
{
monoWave[h] = BitConverter.ToInt16(waveStream, i);
h++;
}
return monoWave;
}
private int GetMaxSound(short[] wave)
{
int maxSound = 0;
for (int i = 0; i < wave.Length; i++)
{
maxSound = Math.Max(maxSound, Math.Abs(wave[i]));
}
return maxSound;
}
so when i monitor it from this test here it won't crash if i keep sound levels to "normal"
[Test]
public void TestSound()
{
var waveIn = new WaveIn();
waveIn.MaxSoundLevel += new WaveIn.MaxSoundHandler(waveIn_MaxSoundLevel);
waveIn.StartRecording();
Console.WriteLine("Starting to record");
Thread.Sleep(4800); //record for 4.8 seconds.
waveIn.StopRecording();
Console.WriteLine("Done Recording");
}
void waveIn_MaxSoundLevel(int MaxSound)
{
Console.WriteLine("MaxSound:{0}", MaxSound);
}
here is my output
MaxSound:28
MaxSound:24
MaxSound:31
MaxSound:17
MaxSound:18760
Unhandled Exception: System.OverflowException: Negating the minimum value of a twos complement number is invalid.
I once got it to give me MaxSound:32767 (0x7FFF).
So i figured that my problem lied within it trying to convert a 32 bit number to a 16 bit number which is why i switched GetMaxSound from short to int. So I don't know. I am stumped. So why am I having this problem? doesn't my wave suggest it's max is 32,767 and that the winmm.dll would know that and not go past that? and since it is just converting 2 bytes of data to a short should it never encounter this problem? Please help :)
My solution, for those who may be looking into this, was fairly simple in nature. A 16bit signed number's maximum positive value is 32767. it's maximum negative number is -32768. If you take the absolute value of 32768 and try to put it into a 16 bit number it will result in a overflow exception being thrown. So the solution is to cast the short value to a 32 bit number before i try to take the absolute value of it. Here is the corrected function
private int GetMaxSound(short[] wave)
{
int maxSound = 0;
for (int i = 0; i < wave.Length; i++)
{
maxSound = Math.Max(maxSound, Math.Abs((int)wave[i]));
}
return maxSound;
}
I could probably just have stuck with an unsigned number as well by using ushort but the Math.Abs does
I've successfully read a PE header from an unmanaged module loaded into memory by another process. What I'd like to do now is read the names of this module's exports. Basically, this is what I have so far (I've left out a majority of the PE parsing code, because I already know it works):
Extensions
public static IntPtr Increment(this IntPtr ptr, int amount)
{
return new IntPtr(ptr.ToInt64() + amount);
}
public static T ToStruct<T>(this byte[] data)
{
GCHandle handle = GCHandle.Alloc(data, GCHandleType.Pinned);
T result = (T)Marshal.PtrToStructure(handle.AddrOfPinnedObject(), typeof(T));
handle.Free();
return result;
}
public static byte[] ReadBytes(this Process process, IntPtr baseAddress, int size)
{
int bytesRead;
byte[] bytes = new byte[size];
Native.ReadProcessMemory(process.Handle, baseAddress, bytes, size, out bytesRead);
return bytes;
}
public static T ReadStruct<T>(this Process process, IntPtr baseAddress)
{
byte[] bytes = ReadBytes(process, baseAddress, Marshal.SizeOf(typeof(T)));
return bytes.ToStruct<T>();
}
public static string ReadString(this Process process, IntPtr baseAddress, int size)
{
byte[] bytes = ReadBytes(process, baseAddress, size);
return Encoding.ASCII.GetString(bytes);
}
GetExports()
Native.IMAGE_DATA_DIRECTORY dataDirectory =
NtHeaders.OptionalHeader.DataDirectory[Native.IMAGE_DIRECTORY_ENTRY_EXPORT];
if (dataDirectory.VirtualAddress > 0 && dataDirectory.Size > 0)
{
Native.IMAGE_EXPORT_DIRECTORY exportDirectory =
_process.ReadStruct<Native.IMAGE_EXPORT_DIRECTORY>(
_baseAddress.Increment((int)dataDirectory.VirtualAddress));
IntPtr namesAddress = _baseAddress.Increment((int)exportDirectory.AddressOfNames);
IntPtr nameOrdinalsAddress = _baseAddress.Increment((int)exportDirectory.AddressOfNameOrdinals);
IntPtr functionsAddress = _baseAddress.Increment((int)exportDirectory.AddressOfFunctions);
for (int i = 0; i < exportDirectory.NumberOfFunctions; i++)
{
Console.WriteLine(_process.ReadString(namesAddress.Increment(i * 4), 64));
}
}
When I run this, all I get is a pattern of double question marks, then completely random characters. I know the header is being read correctly, because the signatures are correct. The problem has to lie in the way that I'm iterating over the function list.
The code at this link seems to suggest that the names and ordinals form a matched pair of arrays, counted up to NumberOfNames, and that the functions are separate. So your loop may be iterating the wrong number of times, but that doesn't explain why you're seeing bad strings from the very beginning.
For just printing names, I'm having success with a loop like the one shown below. I think the call to ImageRvaToVa may be what you need to get the correct strings? However I don't know whether that function will work unless you've actually loaded the image by calling MapAndLoad -- that's what the documentation requests, and the mapping did not seem to work in some quick experiments I did using LoadLibrary instead.
Here's the pInvoke declaration:
[DllImport("DbgHelp.dll", CallingConvention = CallingConvention.StdCall), SuppressUnmanagedCodeSecurity]
public static extern IntPtr ImageRvaToVa(
IntPtr NtHeaders,
IntPtr Base,
uint Rva,
IntPtr LastRvaSection);
and here's my main loop:
LOADED_IMAGE loadedImage = ...; // populated with MapAndLoad
IMAGE_EXPORT_DIRECTORY* pIID = ...; // populated with ImageDirectoryEntryToData
uint* pFuncNames = (uint*)
ImageRvaToVa(
loadedImage.FileHeader,
loadedImage.MappedAddress,
pIID->AddressOfNames,
IntPtr.Zero);
for (uint i = 0; i < pIID->NumberOfNames; i++ )
{
uint funcNameRVA = pFuncNames[i];
if (funcNameRVA != 0)
{
char* funcName =
(char*) (ImageRvaToVa(loadedImage.FileHeader,
loadedImage.MappedAddress,
funcNameRVA,
IntPtr.Zero));
var name = Marshal.PtrToStringAnsi((IntPtr) funcName);
Console.WriteLine(" funcName: {0}", name);
}
}