Using NaN instead of 0.0

FastRng/Double/Distributions/ChiSquare.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -24,7 +25,7 @@ namespace FastRng.Double.Distributions
         public async ValueTask<double> GetDistributedValue(CancellationToken token)
         {
             if (this.Random == null)
-                return 0.0;
+                return System.Double.NaN;
 
             return await this.Random.NextNumber(new Gamma{ Shape = 0.5 * this.DegreesOfFreedom, Scale = 2.0 }, token);
         }

FastRng/Double/Distributions/Exponential.cs

@@ -25,7 +25,7 @@ namespace FastRng.Double.Distributions
         public async ValueTask<double> GetDistributedValue(CancellationToken token)
         {
             if (this.Random == null)
-                return 0.0;
+                return System.Double.NaN;
 
             if(this.Mean == 1.0)
                 return -Math.Log(await this.Random.GetUniform(token));

FastRng/Double/Distributions/Gamma.cs

@@ -29,7 +29,7 @@ namespace FastRng.Double.Distributions
         public async ValueTask<double> GetDistributedValue(CancellationToken token)
         {
             if (this.Random == null)
-                return 0.0;
+                return System.Double.NaN;
             
             // Implementation based on "A Simple Method for Generating Gamma Variables"
             // by George Marsaglia and Wai Wan Tsang.  ACM Transactions on Mathematical Software

FastRng/Double/Distributions/Normal.cs

@@ -27,7 +27,7 @@ namespace FastRng.Double.Distributions
         public async ValueTask<double> GetDistributedValue(CancellationToken token = default)
         {
             if (this.Random == null)
-                return 0.0;
+                return System.Double.NaN;
 
             var u1 = await this.Random.GetUniform(token);
             var u2 = await this.Random.GetUniform(token);

FastRng/Double/Distributions/Uniform.cs

@@ -7,6 +7,6 @@ namespace FastRng.Double.Distributions
     {
         public IRandom Random { get; set; }
         
-        public async ValueTask<double> GetDistributedValue(CancellationToken token = default) => this.Random == null ? 0.0 : await this.Random.GetUniform(token);
+        public async ValueTask<double> GetDistributedValue(CancellationToken token = default) => this.Random == null ? System.Double.NaN : await this.Random.GetUniform(token);
     }
 }