Reverts Random.Decimal() implementation from PR 300 to previous v29 implementation. #319 #320

Author: bchavez

HISTORY.md

@@ -1,10 +1,15 @@
+## v30.0.4
+Release Date: 2020-08-15
+
+* Issue 319: The `Random.Decimal()` implementation reverted to previous v29 implementation. Avoids `System.OverflowException` when calling `Random.Decimal(0, decimal.MaxValue)`. The v30 implementation moved to `Bogus.Extensions` namespace as `Random.Decimal2()` which can generate more decimal precision.
+
 ## v30.0.3
-Release Date: 2020-08-13
+Release Date: 2020-08-13, UNPUBLISHED FROM NUGET
 
 * Added `f.Address.CountryOfUnitedKingdom()` extension method in `Bogus.Extensions.UnitedKingdom`.
 
 ## v30.0.2
-Release Date: 2020-08-05
+Release Date: 2020-08-05, UNPUBLISHED FROM NUGET
 
 * Deterministic sequences may have changed.
 * Promoted v30.0.1-beta-4 to v30.0.2 release.

Source/Bogus.Tests/GitHubIssues/Issue319.cs

@@ -0,0 +1,37 @@
+using System;
+using Bogus.Extensions;
+using FluentAssertions;
+using Xunit;
+
+namespace Bogus.Tests.GitHubIssues
+{
+   public class Issue319 : SeededTest
+   {
+      [Fact]
+      public void can_generate_decimal_edge_case()
+      {
+         var r = new Randomizer();
+
+         Action a = () =>
+            {
+               r.Decimal(0m, decimal.MaxValue);
+               r.Decimal(0m, decimal.MaxValue);
+               r.Decimal(0m, decimal.MaxValue);
+               r.Decimal(0m, decimal.MaxValue);
+            };
+         a.Should().NotThrow();
+      }
+
+      [Fact]
+      public void decimal2_should_throw_on_edge_case()
+      {
+         var r = new Randomizer();
+         Action a = () =>
+            {
+               r.Decimal2(0, decimal.MaxValue);
+            };
+
+         a.Should().Throw<OverflowException>();
+      }
+   }
+}

Source/Bogus.Tests/RandomizerTest.cs

@@ -194,7 +194,7 @@ public void generate_double_with_min_and_max()
       [Fact]
       public void generate_decimal_with_min_and_max()
       {
-         r.Decimal(2.2m, 5.2m).Should().Be(3.8697355489728032005903907232m);
+         r.Decimal(2.2m, 5.2m).Should().Be(4.0105668499183690m);
       }
 
       [Fact]

Source/Bogus/Extensions/ExtensionsForRandomizer.cs

@@ -0,0 +1,45 @@
+namespace Bogus.Extensions
+{
+   public static class ExtensionsForRandomizer
+   {
+      /// <summary>
+      /// Get a random decimal, between 0.0 and 1.0.
+      /// </summary>
+      /// <param name="min">Minimum, default 0.0</param>
+      /// <param name="max">Maximum, default 1.0</param>
+      public static decimal Decimal2(this Randomizer r, decimal min = 0.0m, decimal max = 1.0m)
+      {
+         // Decimal: 128 bits wide
+         //   bit 0: sign bit
+         //   bit 1-10: not used
+         //   bit 11-15: scale (values 29, 30, 31 not used)
+         //   bit 16-31: not used
+         //   bit 32-127: mantissa (96 bits)
+
+         // Max value: 00000000 FFFFFFFF FFFFFFFF FFFFFFFF
+         //          = 79228162514264337593543950335
+
+         // Max value with max scaling: 001C0000  FFFFFFFF  FFFFFFFF  FFFFFFFF
+         //                           = 7.9228162514264337593543950335
+
+         // Step 1: Generate a value with uniform distribution between 0 and this value.
+         // This ensures the greatest level of precision in the distribution of bits;
+         // the resulting value, after it is adjusted into the caller's desired range,
+         // should not skip any possible values at the least significant end of the
+         // mantissa.
+
+         int lowBits = r.Number(int.MinValue, int.MaxValue);
+         int middleBits = r.Number(int.MinValue, int.MaxValue);
+         int highBits = r.Number(int.MinValue, int.MaxValue);
+
+         const int Scale = 28;
+
+         decimal result = new decimal(lowBits, middleBits, highBits, isNegative: false, Scale);
+
+         // Step 2: Scale the value and adjust it to the desired range. This may decrease
+         // the accuracy by adjusting the scale as necessary, but we get the best possible
+         // outcome by starting with the most precise scale.
+         return result * (max - min) / 7.9228162514264337593543950335m + min;
+      }
+   }
+}

Source/Bogus/Randomizer.cs

@@ -194,37 +194,7 @@ public double Double(double min = 0.0d, double max = 1.0d)
       /// <param name="max">Maximum, default 1.0</param>
       public decimal Decimal(decimal min = 0.0m, decimal max = 1.0m)
       {
-         // Decimal: 128 bits wide
-         //   bit 0: sign bit
-         //   bit 1-10: not used
-         //   bit 11-15: scale (values 29, 30, 31 not used)
-         //   bit 16-31: not used
-         //   bit 32-127: mantissa (96 bits)
-
-         // Max value: 00000000 FFFFFFFF FFFFFFFF FFFFFFFF
-         //          = 79228162514264337593543950335
-
-         // Max value with max scaling: 001C0000  FFFFFFFF  FFFFFFFF  FFFFFFFF
-         //                           = 7.9228162514264337593543950335
-
-         // Step 1: Generate a value with uniform distribution between 0 and this value.
-         // This ensures the greatest level of precision in the distribution of bits;
-         // the resulting value, after it is adjusted into the caller's desired range,
-         // should not skip any possible values at the least significant end of the
-         // mantissa.
-
-         int lowBits = Number(int.MinValue, int.MaxValue);
-         int middleBits = Number(int.MinValue, int.MaxValue);
-         int highBits = Number(int.MinValue, int.MaxValue);
-
-         const int Scale = 28;
-
-         decimal result = new decimal(lowBits, middleBits, highBits, isNegative: false, Scale);
-
-         // Step 2: Scale the value and adjust it to the desired range. This may decrease
-         // the accuracy by adjusting the scale as necessary, but we get the best possible
-         // outcome by starting with the most precise scale.
-         return result * (max - min) / 7.9228162514264337593543950335m + min;
+         return Convert.ToDecimal(Double()) * (max - min) + min;
       }
 
       /// <summary>