More efficient reading

src/ImageSharp/IO/BufferedReadStream.cs

@@ -223,20 +223,16 @@ namespace SixLabors.ImageSharp.IO
                 this.stream.Seek(this.readerPosition, SeekOrigin.Begin);
             }
 
-            int n = this.stream.Read(this.readBuffer, 0, BufferLength);
-
             // Read doesn't always guarantee the full returned length so read a byte
             // at a time until we get either our count or hit the end of the stream.
-            int i = 0;
-            while (n < BufferLength && i != -1)
+            int n = 0;
+            int i;
+            do
             {
-                i = this.stream.ReadByte();
-
-                if (i != -1)
-                {
-                    this.readBuffer[n++] = (byte)i;
-                }
+                i = this.stream.Read(this.readBuffer, n, BufferLength - n);
+                n += i;
             }
+            while (n < BufferLength && i > 0);
 
             this.readBufferIndex = 0;
         }
@@ -271,20 +267,16 @@ namespace SixLabors.ImageSharp.IO
                 this.stream.Seek(this.readerPosition, SeekOrigin.Begin);
             }
 
-            int n = this.stream.Read(buffer, offset, count);
-
             // Read doesn't always guarantee the full returned length so read a byte
             // at a time until we get either our count or hit the end of the stream.
-            int i = 0;
-            while (n < count && i != -1)
+            int n = 0;
+            int i;
+            do
             {
-                i = this.stream.ReadByte();
-
-                if (i != -1)
-                {
-                    buffer[n++] = (byte)i;
-                }
+                i = this.stream.Read(buffer, n, count - n);
+                n += i;
             }
+            while (n < count && i > 0);
 
             this.Position += n;
 

src/ImageSharp/Image.Decode.cs

@@ -60,20 +60,16 @@ namespace SixLabors.ImageSharp
             {
                 long startPosition = stream.Position;
 
-                int n = stream.Read(buffer.Array, 0, headerSize);
-
                 // Read doesn't always guarantee the full returned length so read a byte
                 // at a time until we get either our count or hit the end of the stream.
-                int i = 0;
-                while (n < headerSize && i != -1)
+                int n = 0;
+                int i;
+                do
                 {
-                    i = stream.ReadByte();
-
-                    if (i != -1)
-                    {
-                        buffer.Array[n++] = (byte)i;
-                    }
+                    i = stream.Read(buffer.Array, n, headerSize - n);
+                    n += i;
                 }
+                while (n < headerSize && i > 0);
 
                 stream.Position = startPosition;