在从C++转换为C#的代码中,我应该使用什么而不是memcpy？

Question

在从C++转换为C#的代码中,我应该使用什么而不是memcpy？

这条线在这里:

memcpy(v[0], b_y1[0], 160U * sizeof(double));

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where v和b_y1area double arrays(double[]).

这条线到底在做什么？它是通过将MatLab转换为C++到C#生成的.如果需要,我可以提供以下全部功能.

Answer 1

AAA*_*ddd 8

有很多方法可以做到这一点.如果您选择并使用,请导入Dllmemcpy

不过你也可以用

Buffer.BlockCopy

将从特定偏移量开始的源数组复制指定数量的字节复制到从特定偏移量开始的目标数组.

Array.Copy

将一个Array中的一系列元素复制到另一个Array,并根据需要执行类型转换和装箱.

已逐渐手动复制项目
甚至更快使用,fixed并unsafe和指针

但是,如果你真的想要的速度,Array.Copy而且Buffer.BlockCopy可能是你最快最匹配

基准

只因为我很烦人,我打开了基准测试程序.比赛你的马!

----------------------------------------------------------------------------
Operating System : Microsoft Windows 10 Pro
Version          : 10.0.17134
----------------------------------------------------------------------------
CPU Name         : Intel(R) Core(TM) i7-3770K CPU @ 3.50GHz
Description      : Intel64 Family 6 Model 58 Stepping 9
Cores (Threads)  : 4 (8)      : Architecture  : x64
Clock Speed      : 3901 MHz   : Bus Speed     : 100 MHz
L2Cache          : 1 MB       : L3Cache       : 8 MB
----------------------------------------------------------------------------

Total Benchmarks : Inputs (1) * Scales (7) * Benchmarks (4) * Runs (500) = 14,000

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结果1

----------------------------------------------------------------------------
Mode             : Release (64Bit)
Test Framework   : .NET Framework 4.7.1 (CLR 4.0.30319.42000)
----------------------------------------------------------------------------

Total Benchmarks : Inputs (1) * Scales (7) * Benchmarks (4) * Runs (500) = 14,000

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NET Framework 4.7.1

--- Standard input --------------------------------------------------------------------
| Value           |   Average |   Fastest |    Cycles |    Garbage | Test |      Gain |
--- Scale 10 ----------------------------------------------------------- Time 0.994 ---
| ArrayCopy       |  0.005 ms |  0.004 ms |  23.016 K |   7.927 KB | N/A  |   14.98 % |
| ElemCopy        |  0.006 ms |  0.004 ms |  23.591 K |   8.000 KB | N/A  |   12.08 % |
| ElemCopy Unsafe |  0.006 ms |  0.004 ms |  26.426 K |   7.915 KB | N/A  |    0.77 % |
| BlockCopy       |  0.006 ms |  0.004 ms |  26.295 K |   7.836 KB | Base |    0.00 % |
--- Scale 100 ---------------------------------------------------------- Time 1.124 ---
| ArrayCopy       |  0.005 ms |  0.004 ms |  20.581 K |   7.937 KB | N/A  |    1.60 % |
| BlockCopy       |  0.005 ms |  0.004 ms |  20.915 K |   8.000 KB | Base |    0.00 % |
| ElemCopy        |  0.005 ms |  0.004 ms |  21.836 K |   8.000 KB | N/A  |   -4.15 % |
| ElemCopy Unsafe |  0.005 ms |  0.004 ms |  22.357 K |   7.970 KB | N/A  |  -10.85 % |
--- Scale 1,000 -------------------------------------------------------- Time 1.322 ---
| ArrayCopy       |  0.005 ms |  0.005 ms |  23.106 K |   8.000 KB | N/A  |    6.31 % |
| ElemCopy Unsafe |  0.006 ms |  0.005 ms |  24.075 K |   8.000 KB | N/A  |    1.41 % |
| ElemCopy        |  0.006 ms |  0.005 ms |  24.392 K |   8.000 KB | N/A  |    0.46 % |
| BlockCopy       |  0.006 ms |  0.004 ms |  24.766 K |   8.015 KB | Base |    0.00 % |
--- Scale 10,000 ------------------------------------------------------- Time 1.727 ---
| BlockCopy       |  0.013 ms |  0.009 ms |  51.749 K |  86.172 KB | Base |    0.00 % |
| ArrayCopy       |  0.016 ms |  0.014 ms |  61.467 K |  86.172 KB | N/A  |  -23.61 % |
| ElemCopy Unsafe |  0.017 ms |  0.015 ms |  63.659 K |  86.172 KB | N/A  |  -28.22 % |
| ElemCopy        |  0.019 ms |  0.016 ms |  70.479 K |  86.172 KB | N/A  |  -41.93 % |
--- Scale 100,000 ------------------------------------------------------ Time 1.825 ---
| BlockCopy       |  0.050 ms |  0.045 ms | 178.829 K | 789.273 KB | Base |    0.00 % |
| ArrayCopy       |  0.101 ms |  0.089 ms | 357.518 K | 789.273 KB | N/A  | -102.24 % |
| ElemCopy Unsafe |  0.121 ms |  0.108 ms | 428.179 K | 789.273 KB | N/A  | -143.35 % |
| ElemCopy        |  0.133 ms |  0.118 ms | 469.168 K | 789.273 KB | N/A  | -166.41 % |
--- Scale 1,000,000 ---------------------------------------------------- Time 4.946 ---
| BlockCopy       |  0.494 ms |  0.409 ms |   1.730 M |   7.637 MB | Base |    0.00 % |
| ElemCopy Unsafe |  1.336 ms |  1.164 ms |   4.674 M |   7.637 MB | N/A  | -170.59 % |
| ArrayCopy       |  1.478 ms |  1.298 ms |   5.169 M |   7.637 MB | N/A  | -199.40 % |
| ElemCopy        |  1.910 ms |  1.607 ms |   6.675 M |   7.637 MB | N/A  | -286.95 % |
--- Scale 10,000,000 -------------------------------------------------- Time 31.376 ---
| BlockCopy       |  5.408 ms |  4.589 ms |  18.896 M |  76.302 MB | Base |    0.00 % |
| ElemCopy Unsafe | 43.981 ms | 35.344 ms | 153.137 M |  76.302 MB | N/A  | -713.21 % |
| ElemCopy        | 46.318 ms | 37.623 ms | 161.225 M |  76.302 MB | N/A  | -756.43 % |
| ArrayCopy       | 48.171 ms | 38.471 ms | 167.548 M |  76.302 MB | N/A  | -790.69 % |
---------------------------------------------------------------------------------------

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结果2

----------------------------------------------------------------------------
Mode             : Release (64Bit)
Test Framework   : .Net Core 2.0 (CLR 4.0.30319.42000)
----------------------------------------------------------------------------

Total Benchmarks : Inputs (1) * Scales (7) * Benchmarks (4) * Runs (500) = 14,000

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.Net Core 2.0

测试1

--- Standard input ----------------------------------------------------------------------
| Value           |   Average |   Fastest |    Cycles |    Garbage | Test |        Gain |
--- Scale 10 ------------------------------------------------------------- Time 1.221 ---
| ElemCopy Unsafe |  0.006 ms |  0.003 ms |  23.940 K |   8.000 KB | N/A  |     13.53 % |
| BlockCopy       |  0.007 ms |  0.004 ms |  27.573 K |   7.923 KB | Base |      0.00 % |
| ArrayCopy       |  0.007 ms |  0.004 ms |  28.341 K |   7.914 KB | N/A  |     -5.98 % |
| ElemCopy        |  0.007 ms |  0.003 ms |  28.939 K |   7.914 KB | N/A  |     -6.12 % |
--- Scale 100 ------------------------------------------------------------ Time 1.333 ---
| BlockCopy       |  0.005 ms |  0.004 ms |  19.855 K |   7.970 KB | Base |      0.00 % |
| ElemCopy        |  0.005 ms |  0.004 ms |  22.061 K |   7.950 KB | N/A  |    -11.44 % |
| ArrayCopy       |  0.005 ms |  0.004 ms |  22.793 K |   8.000 KB | N/A  |    -15.94 % |
| ElemCopy Unsafe |  0.006 ms |  0.004 ms |  23.715 K |   7.999 KB | N/A  |    -21.65 % |
--- Scale 1,000 ---------------------------------------------------------- Time 1.464 ---
| BlockCopy       |  0.005 ms |  0.004 ms |  21.045 K |   8.001 KB | Base |      0.00 % |
| ElemCopy Unsafe |  0.005 ms |  0.004 ms |  21.731 K |   8.016 KB | N/A  |     -5.53 % |
| ElemCopy        |  0.006 ms |  0.004 ms |  24.120 K |   8.000 KB | N/A  |    -17.49 % |
| ArrayCopy       |  0.006 ms |  0.004 ms |  27.113 K |   8.013 KB | N/A  |    -31.62 % |
--- Scale 10,000 --------------------------------------------------------- Time 1.846 ---
| BlockCopy       |  0.010 ms |  0.008 ms |  37.962 K |  86.172 KB | Base |      0.00 % |
| ArrayCopy       |  0.018 ms |  0.014 ms |  67.134 K |  86.172 KB | N/A  |    -83.72 % |
| ElemCopy Unsafe |  0.019 ms |  0.014 ms |  72.097 K |  86.172 KB | N/A  |    -99.35 % |
| ElemCopy        |  0.021 ms |  0.016 ms |  77.657 K |  86.172 KB | N/A  |   -113.22 % |
--- Scale 100,000 -------------------------------------------------------- Time 2.880 ---
| BlockCopy       |  0.027 ms |  0.020 ms | 100.355 K | 789.305 KB | Base |      0.00 % |
| ArrayCopy       |  0.385 ms |  0.289 ms |   1.346 M | 789.305 KB | N/A  | -1,305.09 % |
| ElemCopy Unsafe |  0.404 ms |  0.280 ms |   1.414 M | 789.305 KB | N/A  | -1,374.97 % |
| ElemCopy        |  0.408 ms |  0.322 ms |   1.424 M | 789.305 KB | N/A  | -1,389.61 % |
--- Scale 1,000,000 ----------------------------------------------------- Time 11.892 ---
| BlockCopy       |  0.632 ms |  0.415 ms |   2.198 M |   7.637 MB | Base |      0.00 % |
| ElemCopy        |  4.645 ms |  3.347 ms |  16.159 M |   7.637 MB | N/A  |   -635.36 % |
| ArrayCopy       |  4.706 ms |  3.684 ms |  16.376 M |   7.637 MB | N/A  |   -645.01 % |
| ElemCopy Unsafe |  4.774 ms |  3.467 ms |  16.568 M |   7.637 MB | N/A  |   -655.66 % |
--- Scale 10,000,000 ---------------------------------------------------- Time 35.806 ---
| BlockCopy       |  6.116 ms |  4.635 ms |  21.294 M |  76.302 MB | Base |      0.00 % |
| ElemCopy Unsafe | 44.132 ms | 35.039 ms | 153.807 M |  76.302 MB | N/A  |   -621.63 % |
| ArrayCopy       | 49.990 ms | 40.360 ms | 173.860 M |  76.302 MB | N/A  |   -717.41 % |
| ElemCopy        | 50.552 ms | 38.044 ms | 175.432 M |  76.302 MB | N/A  |   -726.60 % |
-----------------------------------------------------------------------------------------

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输入

public static double[] ArrayOfDouble(int scale)
{
   return Enumerable.Range(1, scale)
                    .Select(x =>_rand.NextDouble())
                    .ToArray();
}

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码

[Test("BlockCopy", "", true)]
public double[] Test1(double[] input, int scale)
{
   var result = new double[scale];
   Buffer.BlockCopy(input, 0, result, 0, input.Length);
   return result;
}

[Test("ArrayCopy", "", false)]
public  double[] Test2(double[] input, int scale)
{
   var result = new double[scale];
   Array.Copy(input, 0, result, 0, input.Length);
   return result;
}

[Test("ElemCopy", "", false)]
public  double[] Test3(double[] input, int scale)
{
   var result = new double[scale];
   for (var i=0; i <input.Length; i++)
      result[i] = input[i];
   return result;
}

[Test("ElemCopy Unsafe", "", false)]
unsafe public  double[] Test4(double[] input, int scale)
{
   var result = new double[scale];
   fixed(double* pInput = input, pResult = result)
   for (var i=0; i <input.Length; i++)
      *(pResult+i) = *(pResult+i);
   return result;
}

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摘要

这应该是一粒盐,任何真正的测试都应该在你自己的系统上进行.然而,这是对我缩放时得到的内容的一个很好的估计

在这种情况下,双打BlockCopy表现非常好,ArrayCopy在高规模下降,我不知道为什么,不安全总是在这些事情上有性能优势,但不能与专用的BCL方法相匹配.

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