c# - 将浮点格式的 char[] 转换为浮点数
问题描述
我有一个char[] salary包含来自string. 我想转换char[] salary为float，但我正在尝试的方法似乎非常慢，即：
float ff = float.Parse(new string(salary));
根据 Visual Studio 的 Performance Profiler，这需要太多的处理：
所以我想知道是否有更快的方法来做到这一点，因为这里的性能很重要。的char[]格式如下：
[ '1', '3', '2', ',', '2', '9']
并且基本上是一个类似 JSON 的浮点数，转换为适合char[].
编辑：
我已经重新格式化了代码，看起来性能影响实际上是从char[]to的转换，而不是从tostring的解析。stringfloat
解决方案
由于这个问题已经从“解析 a 的最快方法是float什么？” string对于“从 a中获取 a 的最快方法是char[]什么？”，我写了一些基准BenchmarkDotNet来比较各种方法。我的发现是，如果你已经有一个char[]，你不能比string(char[])像你已经在做的那样将它传递给构造函数更快。
您说您的输入文件“读入 a byte[]，然后将byte[]代表 的float部分提取到 achar[]中”。由于您有byte组成float文本的 s 隔离在 a 中byte[]，也许您可以通过跳过中间来提高性能char[]。假设你有相当于......
byte[] floatBytes = new byte[] { 0x31, 0x33, 0x32, 0x2C, 0x32, 0x39 }; // "132,29"
...你可以使用Encoding.GetString()...
string floatString = Encoding.ASCII.GetString(floatBytes);
Encoding.GetChars()...这几乎是将结果传递给string(char[])构造函数的两倍...
char[] floatChars = Encoding.ASCII.GetChars(floatBytes);
string floatString = new string(floatChars);
你会发现我的结果中最后列出的那些基准......
BenchmarkDotNet=v0.11.0, OS=Windows 10.0.17134.165 (1803/April2018Update/Redstone4)
Intel Core i7 CPU 860 2.80GHz (Max: 2.79GHz) (Nehalem), 1 CPU, 8 logical and 4 physical cores
Frequency=2732436 Hz, Resolution=365.9738 ns, Timer=TSC
.NET Core SDK=2.1.202
[Host] : .NET Core 2.0.9 (CoreCLR 4.6.26614.01, CoreFX 4.6.26614.01), 64bit RyuJIT
Clr : .NET Framework 4.7.2 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.3131.0
Core : .NET Core 2.0.9 (CoreCLR 4.6.26614.01, CoreFX 4.6.26614.01), 64bit RyuJIT
Method | Runtime | Categories | Mean | Scaled |
----------------------------------------------------- |-------- |----------------- |----------:|-------:|
String_Constructor_CharArray | Clr | char[] => string | 13.51 ns | 1.00 |
String_Concat | Clr | char[] => string | 192.87 ns | 14.27 |
StringBuilder_Local_AppendSingleChar_DefaultCapacity | Clr | char[] => string | 60.74 ns | 4.49 |
StringBuilder_Local_AppendSingleChar_ExactCapacity | Clr | char[] => string | 60.26 ns | 4.46 |
StringBuilder_Local_AppendAllChars_DefaultCapacity | Clr | char[] => string | 51.27 ns | 3.79 |
StringBuilder_Local_AppendAllChars_ExactCapacity | Clr | char[] => string | 49.51 ns | 3.66 |
StringBuilder_Field_AppendSingleChar | Clr | char[] => string | 51.14 ns | 3.78 |
StringBuilder_Field_AppendAllChars | Clr | char[] => string | 32.95 ns | 2.44 |
| | | | |
String_Constructor_CharPointer | Clr | void* => string | 29.28 ns | 1.00 |
String_Constructor_SBytePointer | Clr | void* => string | 89.21 ns | 3.05 |
UnsafeArrayCopy_String_Constructor | Clr | void* => string | 42.82 ns | 1.46 |
| | | | |
Encoding_GetString | Clr | byte[] => string | 37.33 ns | 1.00 |
Encoding_GetChars_String_Constructor | Clr | byte[] => string | 60.83 ns | 1.63 |
SafeArrayCopy_String_Constructor | Clr | byte[] => string | 27.55 ns | 0.74 |
| | | | |
String_Constructor_CharArray | Core | char[] => string | 13.27 ns | 1.00 |
String_Concat | Core | char[] => string | 172.17 ns | 12.97 |
StringBuilder_Local_AppendSingleChar_DefaultCapacity | Core | char[] => string | 58.68 ns | 4.42 |
StringBuilder_Local_AppendSingleChar_ExactCapacity | Core | char[] => string | 59.85 ns | 4.51 |
StringBuilder_Local_AppendAllChars_DefaultCapacity | Core | char[] => string | 40.62 ns | 3.06 |
StringBuilder_Local_AppendAllChars_ExactCapacity | Core | char[] => string | 43.67 ns | 3.29 |
StringBuilder_Field_AppendSingleChar | Core | char[] => string | 54.49 ns | 4.11 |
StringBuilder_Field_AppendAllChars | Core | char[] => string | 31.05 ns | 2.34 |
| | | | |
String_Constructor_CharPointer | Core | void* => string | 22.87 ns | 1.00 |
String_Constructor_SBytePointer | Core | void* => string | 83.11 ns | 3.63 |
UnsafeArrayCopy_String_Constructor | Core | void* => string | 35.30 ns | 1.54 |
| | | | |
Encoding_GetString | Core | byte[] => string | 36.19 ns | 1.00 |
Encoding_GetChars_String_Constructor | Core | byte[] => string | 58.99 ns | 1.63 |
SafeArrayCopy_String_Constructor | Core | byte[] => string | 27.81 ns | 0.77 |
...从运行此代码（需要BenchmarkDotNet汇编和编译/unsafe）...
using System;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using BenchmarkDotNet.Attributes;
namespace StackOverflow_51584129
{
[CategoriesColumn()]
[ClrJob()]
[CoreJob()]
[GroupBenchmarksBy(BenchmarkDotNet.Configs.BenchmarkLogicalGroupRule.ByCategory)]
public class StringCreationBenchmarks
{
private static readonly Encoding InputEncoding = Encoding.ASCII;
private const string InputString = "132,29";
private static readonly byte[] InputBytes = InputEncoding.GetBytes(InputString);
private static readonly char[] InputChars = InputString.ToCharArray();
private static readonly sbyte[] InputSBytes = InputBytes.Select(Convert.ToSByte).ToArray();
private GCHandle _inputBytesHandle;
private GCHandle _inputCharsHandle;
private GCHandle _inputSBytesHandle;
private StringBuilder _builder;
[Benchmark(Baseline = true)]
[BenchmarkCategory("char[] => string")]
public string String_Constructor_CharArray()
{
return new string(InputChars);
}
[Benchmark(Baseline = true)]
[BenchmarkCategory("void* => string")]
public unsafe string String_Constructor_CharPointer()
{
var pointer = (char*) _inputCharsHandle.AddrOfPinnedObject();
return new string(pointer);
}
[Benchmark()]
[BenchmarkCategory("void* => string")]
public unsafe string String_Constructor_SBytePointer()
{
var pointer = (sbyte*) _inputSBytesHandle.AddrOfPinnedObject();
return new string(pointer);
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string String_Concat()
{
return string.Concat(InputChars);
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string StringBuilder_Local_AppendSingleChar_DefaultCapacity()
{
var builder = new StringBuilder();
foreach (var c in InputChars)
builder.Append(c);
return builder.ToString();
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string StringBuilder_Local_AppendSingleChar_ExactCapacity()
{
var builder = new StringBuilder(InputChars.Length);
foreach (var c in InputChars)
builder.Append(c);
return builder.ToString();
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string StringBuilder_Local_AppendAllChars_DefaultCapacity()
{
var builder = new StringBuilder().Append(InputChars);
return builder.ToString();
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string StringBuilder_Local_AppendAllChars_ExactCapacity()
{
var builder = new StringBuilder(InputChars.Length).Append(InputChars);
return builder.ToString();
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string StringBuilder_Field_AppendSingleChar()
{
_builder.Clear();
foreach (var c in InputChars)
_builder.Append(c);
return _builder.ToString();
}
[Benchmark()]
[BenchmarkCategory("char[] => string")]
public string StringBuilder_Field_AppendAllChars()
{
return _builder.Clear().Append(InputChars).ToString();
}
[Benchmark(Baseline = true)]
[BenchmarkCategory("byte[] => string")]
public string Encoding_GetString()
{
return InputEncoding.GetString(InputBytes);
}
[Benchmark()]
[BenchmarkCategory("byte[] => string")]
public string Encoding_GetChars_String_Constructor()
{
var chars = InputEncoding.GetChars(InputBytes);
return new string(chars);
}
[Benchmark()]
[BenchmarkCategory("byte[] => string")]
public string SafeArrayCopy_String_Constructor()
{
var chars = new char[InputString.Length];
for (int i = 0; i < InputString.Length; i++)
chars[i] = Convert.ToChar(InputBytes[i]);
return new string(chars);
}
[Benchmark()]
[BenchmarkCategory("void* => string")]
public unsafe string UnsafeArrayCopy_String_Constructor()
{
fixed (char* chars = new char[InputString.Length])
{
var bytes = (byte*) _inputBytesHandle.AddrOfPinnedObject();
for (int i = 0; i < InputString.Length; i++)
chars[i] = Convert.ToChar(bytes[i]);
return new string(chars);
}
}
[GlobalSetup(Targets = new[] { nameof(StringBuilder_Field_AppendAllChars), nameof(StringBuilder_Field_AppendSingleChar) })]
public void SetupStringBuilderField()
{
_builder = new StringBuilder();
}
[GlobalSetup(Target = nameof(UnsafeArrayCopy_String_Constructor))]
public void SetupBytesHandle()
{
_inputBytesHandle = GCHandle.Alloc(InputBytes, GCHandleType.Pinned);
}
[GlobalCleanup(Target = nameof(UnsafeArrayCopy_String_Constructor))]
public void CleanupBytesHandle()
{
_inputBytesHandle.Free();
}
[GlobalSetup(Target = nameof(String_Constructor_CharPointer))]
public void SetupCharsHandle()
{
_inputCharsHandle = GCHandle.Alloc(InputChars, GCHandleType.Pinned);
}
[GlobalCleanup(Target = nameof(String_Constructor_CharPointer))]
public void CleanupCharsHandle()
{
_inputCharsHandle.Free();
}
[GlobalSetup(Target = nameof(String_Constructor_SBytePointer))]
public void SetupSByteHandle()
{
_inputSBytesHandle = GCHandle.Alloc(InputSBytes, GCHandleType.Pinned);
}
[GlobalCleanup(Target = nameof(String_Constructor_SBytePointer))]
public void CleanupSByteHandle()
{
_inputSBytesHandle.Free();
}
public static void Main(string[] args)
{
BenchmarkDotNet.Running.BenchmarkRunner.Run<StringCreationBenchmarks>();
}
}
}
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