回答編集履歴

Unsafe, Span を比較

2023/09/16 03:18

投稿

KOZ6.0

スコア2736

answer CHANGED Viewed

@@ -1,63 +1,119 @@
 こんなもんでしょうか？
-Span<T> が使えるともっと速くなります。
 ```csharp
 using System;
+using System.Diagnostics;
 using System.IO;
 using System.Runtime.InteropServices;
 using System.Windows.Media.Imaging;
+public static class BitmapImageHelper
+{
-[StructLayout(LayoutKind.Sequential, Pack = 2)]
+    [StructLayout(LayoutKind.Sequential, Pack = 2)]
-private struct BITMAPFILEHEADER {
+    private struct BITMAPFILEHEADER
+    {
-    public ushort bfType;
+        public ushort bfType;
-    public uint bfSize;
+        public uint bfSize;
-    public ushort bfReserved1;
+        public ushort bfReserved1;
-    public ushort bfReserved2;
+        public ushort bfReserved2;
-    public uint bfOffBits;
+        public uint bfOffBits;
+    }
+    [StructLayout(LayoutKind.Sequential)]
+    private struct BITMAPINFOHEADER
+    {
+        public uint biSize;
+        public int biWidth;
+        public int biHeight;
+        public ushort biPlanes;
+        public ushort biBitCount;
+        public uint biCompression;
+        public uint biSizeImage;
+        public int biXPelsPerMeter;
+        public int biYPelsPerMeter;
+        public uint biClrUsed;
+        public uint biClrImportant;
+    }
+    public enum BitmapDirection
+    {
+        TopDown, BottomUp
+    }
+    public static BitmapImage BitmapImageFromFile(
+                                string fileName,
+                                out BitmapDirection direction) {
+        byte[] bytes = File.ReadAllBytes(fileName);
+        direction = GetBitmapDirection(bytes);
+        using (MemoryStream mem = new MemoryStream(bytes)) {
+            BitmapImage bitmap = new BitmapImage();
+            bitmap.BeginInit();
+            bitmap.StreamSource = mem;
+            bitmap.CacheOption = BitmapCacheOption.OnLoad;
+            bitmap.EndInit();
+            bitmap.Freeze();
+            return bitmap;
+        }
+    }
+    public static BitmapDirection GetBitmapDirection(byte[] bytes) {
+        int offset = Marshal.SizeOf(typeof(BITMAPFILEHEADER));
+        int size = Marshal.SizeOf(typeof(BITMAPINFOHEADER));
+        IntPtr ptr = Marshal.AllocCoTaskMem(size);
+        try {
+            Marshal.Copy(bytes, offset, ptr, size);
+            BITMAPINFOHEADER infoHeader = Marshal.PtrToStructure<BITMAPINFOHEADER>(ptr);
+            return infoHeader.biHeight > 0 ? BitmapDirection.BottomUp
+                                           : BitmapDirection.TopDown;
+        } finally {
+            Marshal.FreeCoTaskMem(ptr);
+        }
+    }
 }
+```
-[StructLayout(LayoutKind.Sequential)]
-private struct BITMAPINFOHEADER {
+Unsafe 版とSpan版を作って比較してみました。
-    public uint biSize;
+```csharp
-    public int biWidth;
-    public int biHeight;
-    public ushort biPlanes;
+// Unsafe 版
+public static unsafe BitmapDirection UnsafeGetBitmapDirection(byte[] bytes) {
-    public ushort biBitCount;
+    fixed (byte* lpFileHeader = bytes) {
+        BITMAPINFOHEADER* lpInfoHeader =
+            (BITMAPINFOHEADER*)(lpFileHeader + sizeof(BITMAPFILEHEADER));
+        return lpInfoHeader->biHeight > 0 ? BitmapDirection.BottomUp
-    public uint biCompression;
+                                          : BitmapDirection.TopDown;
-    public uint biSizeImage;
-    public int biXPelsPerMeter;
-    public int biYPelsPerMeter;
-    public uint biClrUsed;
+    }
-    public uint biClrImportant;
 }
+// Span 版
+public static BitmapDirection SpanGetBitmapDirection(byte[] bytes) {
+    int offset = Marshal.SizeOf(typeof(BITMAPFILEHEADER));
+    int size = Marshal.SizeOf(typeof(BITMAPINFOHEADER));
+    Span<byte> span = new Span<byte>(bytes, offset, size);
+    BITMAPINFOHEADER infoHeader = MemoryMarshal.Read<BITMAPINFOHEADER>(span);
+    return infoHeader.biHeight > 0 ? BitmapDirection.BottomUp
-public enum BitmapDirection
+                                   : BitmapDirection.TopDown;
-{
-    TopDown, BottomUp
 }
-public static BitmapImage BitmapImageFromFile(
+public static void TryGetBitmapDirection(string fileName) {
-                            string fileName,
-                            out BitmapDirection direction) {
-    var bytes = File.ReadAllBytes(fileName);
+    byte[] bytes = File.ReadAllBytes(fileName);
-    var ptr = Marshal.AllocHGlobal(bytes.Length);
-    try {
-        Marshal.Copy(bytes, 0, ptr, bytes.Length);
-        var offset = Marshal.SizeOf(typeof(BITMAPFILEHEADER));
-        var header = Marshal.PtrToStructure<BITMAPINFOHEADER>(ptr + offset);
-        direction = header.biHeight >= 0 ? BitmapDirection.BottomUp
+    Watch("GetBitmapDirection", () => { GetBitmapDirection(bytes); });
+    Watch("UnsafeGetBitmapDirection", () => { UnsafeGetBitmapDirection(bytes); });
+    Watch("SpanGetBitmapDirection", () => { SpanGetBitmapDirection(bytes); });
+}
-                                         : BitmapDirection.TopDown;
+public static void Watch(string message, Action action) {
-    } finally {
-        Marshal.FreeHGlobal(ptr);
+    Stopwatch sw = new Stopwatch();
+    sw.Start();
+    for (int i = 0; i < 100000; i++) {
+        action.Invoke();
     }
-    var mem = new MemoryStream(bytes);
-    var bitmap = new BitmapImage();
-    bitmap.BeginInit();
-    bitmap.StreamSource = mem;
-    bitmap.CacheOption = BitmapCacheOption.OnLoad;
-    bitmap.EndInit();
-    bitmap.Freeze();
+    sw.Stop();
-    return bitmap;
+    Console.WriteLine($"{message} {sw.ElapsedMilliseconds}ms");
 }
+結果
+GetBitmapDirection 61ms
+UnsafeGetBitmapDirection 1ms
+SpanGetBitmapDirection 12ms
 ```
-思えば 16bit VB を 32bit VB に書き直したとき、最初にひっかかったのがこれ(BITMAPFILEHEADER)だったなぁ・・・
+Span も速いですが、やはり Unsafe は速かった。

逆だった

2023/09/15 20:57

投稿

KOZ6.0

スコア2736

answer CHANGED Viewed

@@ -45,8 +45,8 @@
         Marshal.Copy(bytes, 0, ptr, bytes.Length);
         var offset = Marshal.SizeOf(typeof(BITMAPFILEHEADER));
         var header = Marshal.PtrToStructure<BITMAPINFOHEADER>(ptr + offset);
-        direction = header.biHeight >= 0 ? BitmapDirection.TopDown
+        direction = header.biHeight >= 0 ? BitmapDirection.BottomUp
-                                         : BitmapDirection.BottomUp;
+                                         : BitmapDirection.TopDown;
     } finally {
         Marshal.FreeHGlobal(ptr);
     }

using

2023/09/15 14:14

投稿

KOZ6.0

スコア2736

answer CHANGED Viewed

@@ -2,6 +2,11 @@
 Span<T> が使えるともっと速くなります。
 ```csharp
+using System;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Windows.Media.Imaging;
 [StructLayout(LayoutKind.Sequential, Pack = 2)]
 private struct BITMAPFILEHEADER {
     public ushort bfType;
@@ -31,7 +36,7 @@
     TopDown, BottomUp
 }
-public static BitmapImage FromBitmapImage(
+public static BitmapImage BitmapImageFromFile(
                             string fileName,
                             out BitmapDirection direction) {
     var bytes = File.ReadAllBytes(fileName);