Guard against div/0 for HeatContainerHelpers (#42213)

Guard against div/0 for HeatContainers

Content.Shared/Temperature/HeatContainer/HeatContainerHelpers.Exchange.cs

@@ -16,9 +16,13 @@ public static partial class HeatContainerHelpers
     /// <returns>The amount of heat in joules that is needed
     /// to bring the containers to thermal equilibrium.</returns>
     /// <example>A positive value indicates heat transfer from a hot cA to a cold cB.</example>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the combined heat capacity of both containers is zero or negative.</exception>
     [PublicAPI]
     public static float EquilibriumHeatQuery(this ref HeatContainer cA, ref HeatContainer cB)
     {
+        var cTotal = cA.HeatCapacity + cB.HeatCapacity;
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(cTotal);
+
         /*
         The solution is derived from the following facts:
         1. Let Q be the amount of heat energy transferred from cA to cB.
@@ -32,7 +36,7 @@ public static partial class HeatContainerHelpers
         7. Solve for Q.
         */
         return (cA.Temperature - cB.Temperature) *
-               (cA.HeatCapacity * cB.HeatCapacity / (cA.HeatCapacity + cB.HeatCapacity));
+               (cA.HeatCapacity * cB.HeatCapacity / cTotal);
     }
 
     /// <summary>
@@ -42,11 +46,14 @@ public static partial class HeatContainerHelpers
     /// <param name="cA">The first <see cref="HeatContainer"/> to exchange heat.</param>
     /// <param name="cB">The second <see cref="HeatContainer"/> to exchange heat with.</param>
     /// <returns>The resulting equilibrium temperature both containers will be at.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the combined heat capacity of both containers is zero or negative.</exception>
     [PublicAPI]
     public static float EquilibriumTemperatureQuery(this ref HeatContainer cA, ref HeatContainer cB)
     {
+        var cTotal = cA.HeatCapacity + cB.HeatCapacity;
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(cTotal);
         // Insert the above solution for Q into T_A_final = T_A_initial - Q / C_A and rearrange the result.
-        return (cA.HeatCapacity * cA.Temperature - cB.HeatCapacity * cB.Temperature) / (cA.HeatCapacity + cB.HeatCapacity);
+        return (cA.HeatCapacity * cA.Temperature - cB.HeatCapacity * cB.Temperature) / cTotal;
     }
 
     /// <summary>
@@ -75,6 +82,7 @@ public static partial class HeatContainerHelpers
         var tFinal = EquilibriumTemperatureQuery(ref cA, ref cB);
         cA.Temperature = tFinal;
         cB.Temperature = tFinal;
+        // Guarded against div/0 in EquilibriumTemperatureQuery: totalHeatCapacity > 0.
         dQ = (tInitialA - tFinal) / cA.HeatCapacity;
     }
 
@@ -120,6 +128,7 @@ public static partial class HeatContainerHelpers
     /// </summary>
     /// <param name="cN">The array of <see cref="HeatContainer"/>s to bring into thermal equilibrium.</param>
     /// <returns>The temperature of all <see cref="HeatContainer"/>s involved after reaching thermal equilibrium.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the combined heat capacity of all containers is zero or negative.</exception>
     [PublicAPI]
     public static float EquilibriumTemperatureQuery(this HeatContainer[] cN)
     {
@@ -161,6 +170,8 @@ public static partial class HeatContainerHelpers
             denominator += c.HeatCapacity;
         }
 
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(denominator);
+
         return numerator / denominator;
     }
 

Content.Shared/Temperature/HeatContainer/HeatContainerHelpers.Merge.cs

@@ -9,13 +9,16 @@ public static partial class HeatContainerHelpers
     /// </summary>
     /// <param name="cA">The first <see cref="HeatContainer"/> to merge. This will be modified to contain the merged result.</param>
     /// <param name="cB">The second <see cref="HeatContainer"/> to merge.</param>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the combined heat capacity of both containers is zero or negative.</exception>
     [PublicAPI]
     public static void Merge(this ref HeatContainer cA, HeatContainer cB)
     {
+        var combinedHeatCapacity = cA.HeatCapacity + cB.HeatCapacity;
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(combinedHeatCapacity);
         var merged = new HeatContainer
         {
-            HeatCapacity = cA.HeatCapacity + cB.HeatCapacity,
-            Temperature = (cA.InternalEnergy + cB.InternalEnergy) / (cA.HeatCapacity + cB.HeatCapacity)
+            HeatCapacity = combinedHeatCapacity,
+            Temperature = (cA.InternalEnergy + cB.InternalEnergy) / combinedHeatCapacity,
         };
 
         cA = merged;
@@ -43,6 +46,7 @@ public static partial class HeatContainerHelpers
     /// </summary>
     /// <param name="cN">The array of <see cref="HeatContainer"/>s to merge.</param>
     /// <returns>A new <see cref="HeatContainer"/> representing the merged result.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the combined heat capacity of all containers is zero or negative.</exception>
     [PublicAPI]
     public static HeatContainer Merge(this HeatContainer[] cN)
     {
@@ -55,6 +59,8 @@ public static partial class HeatContainerHelpers
             totalEnergy += c.InternalEnergy;
         }
 
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(totalHeatCapacity);
+
         var result = new HeatContainer
         {
             HeatCapacity = totalHeatCapacity,

Content.Shared/Temperature/HeatContainer/HeatContainerHelpers.cs

@@ -29,9 +29,11 @@ public static partial class HeatContainerHelpers
     /// <param name="c">The <see cref="HeatContainer"/> to query.</param>
     /// <param name="dQ">The energy in joules to add or remove.</param>
     /// <returns>The resulting temperature in kelvin after the heat change.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the heat capacity of the container is zero or negative.</exception>
     [PublicAPI]
     public static float AddHeatQuery(this ref HeatContainer c, float dQ)
     {
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(c.HeatCapacity);
         // Don't allow the temperature to go below the absolute minimum.
         return Math.Max(0f, c.Temperature + dQ / c.HeatCapacity);
     }
@@ -42,9 +44,11 @@ public static partial class HeatContainerHelpers
     /// </summary>
     /// <param name="c">The <see cref="HeatContainer"/> to modify.</param>
     /// <param name="newHeatCapacity">The new heat capacity to set.</param>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown when the new heat capacity is zero or negative.</exception>
     [PublicAPI]
     public static void SetHeatCapacity(this ref HeatContainer c, float newHeatCapacity)
     {
+        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(c.HeatCapacity);
         var currentEnergy = c.InternalEnergy;
         c.HeatCapacity = newHeatCapacity;
         c.Temperature = currentEnergy / c.HeatCapacity;