diff --git a/osu.Game.Rulesets.Osu/Difficulty/OsuPerformanceCalculator.cs b/osu.Game.Rulesets.Osu/Difficulty/OsuPerformanceCalculator.cs
index 7013ee55c4..f191180630 100644
--- a/osu.Game.Rulesets.Osu/Difficulty/OsuPerformanceCalculator.cs
+++ b/osu.Game.Rulesets.Osu/Difficulty/OsuPerformanceCalculator.cs
@@ -10,7 +10,6 @@ using osu.Game.Rulesets.Osu.Difficulty.Skills;
 using osu.Game.Rulesets.Osu.Mods;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Scoring;
-using osu.Game.Utils;
 
 namespace osu.Game.Rulesets.Osu.Difficulty
 {
@@ -371,10 +370,10 @@ namespace osu.Game.Rulesets.Osu.Difficulty
 
             // Compute the deviation assuming greats and oks are normally distributed, and mehs are uniformly distributed.
             // Begin with greats and oks first. Ignoring mehs, we can be 99% confident that the deviation is not higher than:
-            double deviation = hitWindowGreat / (Math.Sqrt(2) * SpecialFunctions.ErfInv(pLowerBound));
+            double deviation = hitWindowGreat / (Math.Sqrt(2) * DifficultyCalculationUtils.ErfInv(pLowerBound));
 
             double randomValue = Math.Sqrt(2 / Math.PI) * hitWindowOk * Math.Exp(-0.5 * Math.Pow(hitWindowOk / deviation, 2))
-                                 / (deviation * SpecialFunctions.Erf(hitWindowOk / (Math.Sqrt(2) * deviation)));
+                                 / (deviation * DifficultyCalculationUtils.Erf(hitWindowOk / (Math.Sqrt(2) * deviation)));
 
             deviation *= Math.Sqrt(1 - randomValue);
 
diff --git a/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs b/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs
index c29ea3ba73..9e7bf7cb7a 100644
--- a/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs
+++ b/osu.Game.Rulesets.Taiko/Difficulty/TaikoPerformanceCalculator.cs
@@ -5,11 +5,11 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using osu.Game.Rulesets.Difficulty;
+using osu.Game.Rulesets.Difficulty.Utils;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Rulesets.Scoring;
 using osu.Game.Rulesets.Taiko.Objects;
 using osu.Game.Scoring;
-using osu.Game.Utils;
 
 namespace osu.Game.Rulesets.Taiko.Difficulty
 {
@@ -99,7 +99,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             double accScalingExponent = 2 + attributes.MonoStaminaFactor;
             double accScalingShift = 500 - 100 * attributes.MonoStaminaFactor;
 
-            return difficultyValue * Math.Pow(SpecialFunctions.Erf(accScalingShift / (Math.Sqrt(2) * estimatedUnstableRate.Value)), accScalingExponent);
+            return difficultyValue * Math.Pow(DifficultyCalculationUtils.Erf(accScalingShift / (Math.Sqrt(2) * estimatedUnstableRate.Value)), accScalingExponent);
         }
 
         private double computeAccuracyValue(ScoreInfo score, TaikoDifficultyAttributes attributes, bool isConvert)
@@ -139,7 +139,7 @@ namespace osu.Game.Rulesets.Taiko.Difficulty
             double pLowerBound = (n * p + z * z / 2) / (n + z * z) - z / (n + z * z) * Math.Sqrt(n * p * (1 - p) + z * z / 4);
 
             // We can be 99% confident that the deviation is not higher than:
-            return attributes.GreatHitWindow / (Math.Sqrt(2) * SpecialFunctions.ErfInv(pLowerBound));
+            return attributes.GreatHitWindow / (Math.Sqrt(2) * DifficultyCalculationUtils.ErfInv(pLowerBound));
         }
 
         private int totalHits => countGreat + countOk + countMeh + countMiss;
diff --git a/osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils.cs b/osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils.cs
index aeccf2fd55..78df8a139b 100644
--- a/osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils.cs
+++ b/osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils.cs
@@ -6,7 +6,7 @@ using System.Linq;
 
 namespace osu.Game.Rulesets.Difficulty.Utils
 {
-    public static class DifficultyCalculationUtils
+    public static partial class DifficultyCalculationUtils
     {
         /// <summary>
         /// Converts BPM value into milliseconds
diff --git a/osu.Game/Utils/SpecialFunctions.cs b/osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils_ErrorFunction.cs
similarity index 99%
rename from osu.Game/Utils/SpecialFunctions.cs
rename to osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils_ErrorFunction.cs
index 795a84a973..4b89cbe7cc 100644
--- a/osu.Game/Utils/SpecialFunctions.cs
+++ b/osu.Game/Rulesets/Difficulty/Utils/DifficultyCalculationUtils_ErrorFunction.cs
@@ -3,7 +3,6 @@
 
 // All code is referenced from the following:
 // https://github.com/mathnet/mathnet-numerics/blob/master/src/Numerics/SpecialFunctions/Erf.cs
-// https://github.com/mathnet/mathnet-numerics/blob/master/src/Numerics/Optimization/NelderMeadSimplex.cs
 
 /*
  Copyright (c) 2002-2022 Math.NET
@@ -14,12 +13,10 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 
 using System;
 
-namespace osu.Game.Utils
+namespace osu.Game.Rulesets.Difficulty.Utils
 {
-    public class SpecialFunctions
+    public partial class DifficultyCalculationUtils
     {
-        private const double sqrt2_pi = 2.5066282746310005024157652848110452530069867406099d;
-
         /// <summary>
         /// **************************************
         /// COEFFICIENTS FOR METHOD ErfImp       *