Fix noise's bug when coord is negative (#39)

Author: sunnycase

src/MineCase.Algorithm/Noise/PerlinNoise.cs

@@ -192,10 +192,10 @@ public void AddNoise(float[,,] noise, Vector3 offset, Vector3 scale, float noise
 
         private static (int integer, float remainder) Split(float value)
         {
+            value = value % 256;
+            if (value < 0) value += 256;
             var integer = (int)value;
             var remainder = value - integer;
-            integer %= 256;
-            if (integer < 0) integer += 256;
             return (integer, remainder);
         }
 

tests/UnitTest/NoiseTest.cs

@@ -57,7 +57,7 @@ public void TestOctavedPerlinNoise3D()
             using (var file = File.OpenWrite(Path.Combine(RootDir, "OctavedPerlinNoise3D.bmp")))
             using (var image = new Image<ImageSharp.PixelFormats.Rgb24>(xExtent, yExtent))
             {
-                var noise = new OctavedNoise<PerlinNoise>(new PerlinNoise(100), 8, 1);
+                var noise = new OctavedNoise<PerlinNoise>(new PerlinNoise(100), 8, 0.25f);
                 var noiseValue = new float[xExtent, yExtent, 1];
                 noise.Noise(noiseValue, new Vector3(-10, 10, -10), new Vector3(0.1f, 0.1f, 0));
                 for (int x = 0; x < xExtent; x++)