Merge pull request #1655 from SixLabors/js/fix-1616

Use GreatestCommonDivisor to prevent overflow
SixLabors · Jun 11, 2021 · 381dff8 · 381dff8
2 parents 11e31ed + 87aec89
commit 381dff8
Show file tree

Hide file tree

Showing 2 changed files with 5 additions and 2 deletions.
diff --git a/src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeKernelMap.cs b/src/ImageSharp/Processing/Processors/Transforms/Resize/ResizeKernelMap.cs
@@ -130,9 +130,9 @@ public static ResizeKernelMap Calculate<TResampler>(
             int radius = (int)TolerantMath.Ceiling(scale * sampler.Radius);
 
             // 'ratio' is a rational number.
-            // Multiplying it by LCM(sourceSize, destSize)/sourceSize will result in a whole number "again".
+            // Multiplying it by destSize/GCD(sourceSize, destSize) will result in a whole number "again".
             // This value is determining the length of the periods in repeating kernel map rows.
-            int period = Numerics.LeastCommonMultiple(sourceSize, destinationSize) / sourceSize;
+            int period = destinationSize / Numerics.GreatestCommonDivisor(sourceSize, destinationSize);
 
             // the center position at i == 0:
             double center0 = (ratio - 1) * 0.5;

diff --git a/tests/ImageSharp.Tests/Processing/Processors/Transforms/ResizeKernelMapTests.cs b/tests/ImageSharp.Tests/Processing/Processors/Transforms/ResizeKernelMapTests.cs
@@ -80,6 +80,9 @@ public static readonly TheoryData<IResampler, int, int> KernelMapData
             { KnownResamplers.Bicubic, 1680, 1200 },
             { KnownResamplers.Box, 13, 299 },
             { KnownResamplers.Lanczos5, 3032, 600 },
+
+            // Large number. https://github.com/SixLabors/ImageSharp/issues/1616
+            { KnownResamplers.Bicubic, 207773, 51943 }
         };
 
         public static TheoryData<string, int, int> GeneratedImageResizeData =