final

BlueLaminate/BlueLaminate.Core/Tradeups/TradeupMath.cs

@@ -0,0 +1,38 @@
+namespace BlueLaminate.Core.Tradeups;
+
+/// <summary>
+/// The exact float arithmetic of a CS2 tradeup. Kept pure and dependency-free so it
+/// can be unit-tested in isolation and reused verbatim by any frontend.
+/// <para>
+/// The contract: each input float is normalised to its own skin's range FIRST, those
+/// fractions are averaged, and the average is mapped onto the OUTPUT skin's range. The
+/// output float depends only on the average input fraction — a single scalar — which
+/// is what makes the search tractable (see the engine design notes).
+/// </para>
+/// </summary>
+public static class TradeupMath
+{
+    /// <summary>
+    /// Normalises an input float to the fraction of its own skin's wear range:
+    /// <c>(value − min) / (max − min)</c>, clamped to [0,1]. A zero-width range
+    /// (min == max) has no meaningful fraction and yields 0.
+    /// </summary>
+    public static decimal NormalizedFraction(decimal floatValue, decimal skinFloatMin, decimal skinFloatMax)
+    {
+        var span = skinFloatMax - skinFloatMin;
+        if (span <= 0m)
+        {
+            return 0m;
+        }
+
+        var fraction = (floatValue - skinFloatMin) / span;
+        return Math.Clamp(fraction, 0m, 1m);
+    }
+
+    /// <summary>
+    /// Maps an average input fraction onto an output skin's wear range to get the exact
+    /// float the tradeup would produce: <c>avgFraction × (max − min) + min</c>.
+    /// </summary>
+    public static decimal OutputFloat(decimal averageFraction, decimal outputFloatMin, decimal outputFloatMax)
+        => averageFraction * (outputFloatMax - outputFloatMin) + outputFloatMin;
+}