Fix mirror sampling fixes issue 135.

ChangeLog

@@ -5,7 +5,8 @@ NVIDIA Texture Tools version 2.0.9
  * Improve C# / .NET Wrapper
  * Add an XNA Game Studio 3.1 Content Processor to make it easy to utilize NVIDIA Texture Tools in XNA applications.
  * Fix single color DXT1a compressor. Fixes issue 134.
- 
+ * Fix mirror sampling. Fixes issue 135.
+
 NVIDIA Texture Tools version 2.0.8
  * Fix float to fixed image conversion. Patch provided by Alex Pfaffe. Fixes issue 121.
  * ColorBlock::isSingleColor compares only RGB channels. Fixes issue 115.

src/nvimage/FloatImage.cpp

@@ -32,14 +32,17 @@ namespace
 		return f - floor(f);
 	}
 
-	static int mirror(int x, int w)
-	{
-		x = abs(x);
-		while (x >= w) {
-			x = 2 * w - x - 2;
-		}
-		return x;
-	}
+    static int mirror(int x, int w)
+    {
+        if (w == 1) return 0;
+
+        x = abs(x);
+        while (x >= w) {
+            x = abs(w + w - x - 2);
+        }
+
+        return x;
+    }
 }