feat: convert DigitalRoot and Mod to generic math

X10D.Tests/src/Math/UInt32Tests.cs

@@ -11,8 +11,14 @@ public partial class UInt32Tests
     public void DigitalRootShouldBeCorrect()
     {
         const uint value = 238;
+
+#if NET7_0_OR_GREATER
+        Assert.AreEqual(4, value.DigitalRoot());
+        Assert.AreEqual(4, (-value).DigitalRoot());
+#else
         Assert.AreEqual(4U, value.DigitalRoot());
         Assert.AreEqual(4U, (-value).DigitalRoot());
+#endif
     }
 
     [TestMethod]

X10D.Tests/src/Math/UInt64Tests.cs

@@ -11,12 +11,18 @@ public partial class UInt64Tests
     public void DigitalRootShouldBeCorrect()
     {
         const ulong value = 238;
-        Assert.AreEqual(4U, value.DigitalRoot());
 
         // -ulong operator not defined because it might exceed long.MinValue,
         // so instead, cast to long and then negate.
         // HAX.
+
+#if NET7_0_OR_GREATER
+        Assert.AreEqual(4, (-(long)value).DigitalRoot());
+        Assert.AreEqual(4, value.DigitalRoot());
+#else
         Assert.AreEqual(4U, (-(long)value).DigitalRoot());
+        Assert.AreEqual(4U, value.DigitalRoot());
+#endif
     }
 
     [TestMethod]

X10D/src/Math/BigIntegerExtensions.cs

@@ -10,6 +10,7 @@ namespace X10D.Math;
 /// </summary>
 public static class BigIntegerExtensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of this 8-bit integer.
     /// </summary>
@@ -27,6 +28,7 @@ public static int DigitalRoot(this BigInteger value)
         BigInteger root = BigInteger.Abs(value).Mod(9);
         return (int)(root == 0 ? 9 : root);
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 64-bit signed integer.
@@ -155,6 +157,7 @@ public static BigInteger LowestCommonMultiple(this BigInteger value, BigInteger
         return value * other / value.GreatestCommonFactor(other);
     }
 
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Performs a modulo operation which supports a negative dividend.
     /// </summary>
@@ -176,6 +179,7 @@ public static BigInteger Mod(this BigInteger dividend, BigInteger divisor)
         BigInteger r = dividend % divisor;
         return r < 0 ? r + divisor : r;
     }
+#endif
 
     /// <summary>
     ///     Returns the multiplicative persistence of a specified value.

X10D/src/Math/BinaryIntegerExtensions.cs

@@ -0,0 +1,58 @@
+#if NET7_0_OR_GREATER
+using System.Diagnostics.Contracts;
+using System.Globalization;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using X10D.CompilerServices;
+
+namespace X10D.Math;
+
+/// <summary>
+///     Math-related extension methods for <see cref="IBinaryInteger{TSelf}" />.
+/// </summary>
+public static class BinaryIntegerExtensions
+{
+    /// <summary>
+    ///     Computes the digital root of this integer.
+    /// </summary>
+    /// <param name="value">The value whose digital root to compute.</param>
+    /// <returns>The digital root of <paramref name="value" />.</returns>
+    /// <remarks>The digital root is defined as the recursive sum of digits until that result is a single digit.</remarks>
+    /// <remarks>
+    ///     <para>The digital root is defined as the recursive sum of digits until that result is a single digit.</para>
+    ///     <para>For example, the digital root of 239 is 5: <c>2 + 3 + 9 = 14</c>, then <c>1 + 4 = 5</c>.</para>
+    /// </remarks>
+    [Pure]
+    [MethodImpl(CompilerResources.MethodImplOptions)]
+    public static int DigitalRoot<TInteger>(this TInteger value)
+        where TInteger : IBinaryInteger<TInteger>
+    {
+        var nine = TInteger.CreateChecked(9);
+        TInteger root = TInteger.Abs(value).Mod(nine);
+        return int.CreateChecked(root == TInteger.Zero ? nine : root);
+    }
+
+    /// <summary>
+    ///     Performs a modulo operation which supports a negative dividend.
+    /// </summary>
+    /// <param name="dividend">The dividend.</param>
+    /// <param name="divisor">The divisor.</param>
+    /// <returns>The result of <c>dividend mod divisor</c>.</returns>
+    /// <remarks>
+    ///     The <c>%</c> operator (commonly called the modulo operator) in C# is not defined to be modulo, but is instead
+    ///     remainder. This quirk inherently makes it difficult to use modulo in a negative context, as <c>x % y</c> where x is
+    ///     negative will return a negative value, akin to <c>-(x % y)</c>, even if precedence is forced. This method provides a
+    ///     modulo operation which supports negative dividends.
+    /// </remarks>
+    /// <author>ShreevatsaR, https://stackoverflow.com/a/1082938/1467293</author>
+    /// <license>CC-BY-SA 2.5</license>
+    [Pure]
+    [MethodImpl(CompilerResources.MethodImplOptions)]
+    public static TInteger Mod<TInteger>(this TInteger dividend, TInteger divisor)
+        where TInteger : IBinaryInteger<TInteger>
+    {
+        TInteger r = dividend % divisor;
+        return r < TInteger.Zero ? r + divisor : r;
+    }
+}
+#endif

X10D/src/Math/ByteExtensions.cs

@@ -9,6 +9,7 @@ namespace X10D.Math;
 /// </summary>
 public static class ByteExtensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of this 8-bit integer.
     /// </summary>
@@ -26,6 +27,7 @@ public static byte DigitalRoot(this byte value)
         int root = value % 9;
         return (byte)(root == 0 ? 9 : root);
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 8-bit unsigned integer.

X10D/src/Math/Int16Extensions.cs

@@ -9,6 +9,7 @@ namespace X10D.Math;
 /// </summary>
 public static class Int16Extensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of this 16-bit integer.
     /// </summary>
@@ -25,6 +26,7 @@ public static short DigitalRoot(this short value)
         short root = System.Math.Abs(value).Mod(9);
         return root < 1 ? (short)(9 - root) : root;
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 16-bit signed integer.
@@ -125,6 +127,7 @@ public static short LowestCommonMultiple(this short value, short other)
         return (short)((long)value).LowestCommonMultiple(other);
     }
 
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Performs a modulo operation which supports a negative dividend.
     /// </summary>
@@ -146,6 +149,7 @@ public static short Mod(this short dividend, short divisor)
         int r = dividend % divisor;
         return (short)(r < 0 ? r + divisor : r);
     }
+#endif
 
     /// <summary>
     ///     Returns the multiplicative persistence of a specified value.

X10D/src/Math/Int32Extensions.cs

@@ -9,6 +9,7 @@ namespace X10D.Math;
 /// </summary>
 public static class Int32Extensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of this 32-bit integer.
     /// </summary>
@@ -25,6 +26,7 @@ public static int DigitalRoot(this int value)
         int root = System.Math.Abs(value).Mod(9);
         return root < 1 ? 9 - root : root;
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 32-bit signed integer.
@@ -125,6 +127,7 @@ public static int LowestCommonMultiple(this int value, int other)
         return (int)((long)value).LowestCommonMultiple(other);
     }
 
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Performs a modulo operation which supports a negative dividend.
     /// </summary>
@@ -146,6 +149,7 @@ public static int Mod(this int dividend, int divisor)
         int r = dividend % divisor;
         return r < 0 ? r + divisor : r;
     }
+#endif
 
     /// <summary>
     ///     Returns the multiplicative persistence of a specified value.

X10D/src/Math/Int64Extensions.cs

@@ -9,6 +9,7 @@ namespace X10D.Math;
 /// </summary>
 public static class Int64Extensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of this 64-bit integer.
     /// </summary>
@@ -25,6 +26,7 @@ public static long DigitalRoot(this long value)
         long root = System.Math.Abs(value).Mod(9L);
         return root < 1L ? 9L - root : root;
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 64-bit signed integer.
@@ -164,6 +166,7 @@ public static long LowestCommonMultiple(this long value, long other)
         return value * other / value.GreatestCommonFactor(other);
     }
 
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Performs a modulo operation which supports a negative dividend.
     /// </summary>
@@ -185,6 +188,7 @@ public static long Mod(this long dividend, long divisor)
         long r = dividend % divisor;
         return r < 0 ? r + divisor : r;
     }
+#endif
 
     /// <summary>
     ///     Returns the multiplicative persistence of a specified value.

X10D/src/Math/SByteExtensions.cs

@@ -10,6 +10,7 @@ namespace X10D.Math;
 [CLSCompliant(false)]
 public static class SByteExtensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of this 32-bit integer.
     /// </summary>
@@ -26,6 +27,7 @@ public static sbyte DigitalRoot(this sbyte value)
         int root = System.Math.Abs(value).Mod(9);
         return (sbyte)(root < 1 ? 9 - root : root);
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 8-bit signed integer.
@@ -126,6 +128,7 @@ public static sbyte LowestCommonMultiple(this sbyte value, sbyte other)
         return (sbyte)((long)value).LowestCommonMultiple(other);
     }
 
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Performs a modulo operation which supports a negative dividend.
     /// </summary>
@@ -147,6 +150,7 @@ public static sbyte Mod(this sbyte dividend, sbyte divisor)
         int r = dividend % divisor;
         return (sbyte)(r < 0 ? r + divisor : r);
     }
+#endif
 
     /// <summary>
     ///     Returns the multiplicative persistence of a specified value.

X10D/src/Math/UInt16Extensions.cs

@@ -10,6 +10,7 @@ namespace X10D.Math;
 [CLSCompliant(false)]
 public static class UInt16Extensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of the current 16-bit unsigned integer.
     /// </summary>
@@ -26,6 +27,7 @@ public static ushort DigitalRoot(this ushort value)
         var root = (ushort)(value % 9);
         return (ushort)(root == 0 ? 9 : root);
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 16-bit unsigned integer.

X10D/src/Math/UInt32Extensions.cs

@@ -10,6 +10,7 @@ namespace X10D.Math;
 [CLSCompliant(false)]
 public static class UInt32Extensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of the current 32-bit unsigned integer.
     /// </summary>
@@ -26,6 +27,7 @@ public static uint DigitalRoot(this uint value)
         uint root = value % 9;
         return root == 0 ? 9 : root;
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 32-bit unsigned integer.

X10D/src/Math/UInt64Extensions.cs

@@ -10,6 +10,7 @@ namespace X10D.Math;
 [CLSCompliant(false)]
 public static class UInt64Extensions
 {
+#if !NET7_0_OR_GREATER
     /// <summary>
     ///     Computes the digital root of the current 64-bit unsigned integer.
     /// </summary>
@@ -26,6 +27,7 @@ public static ulong DigitalRoot(this ulong value)
         ulong root = value % 9;
         return root == 0 ? 9 : root;
     }
+#endif
 
     /// <summary>
     ///     Returns the factorial of the current 64-bit unsigned integer.

X10D/src/Time/Int16Extensions.cs

@@ -32,7 +32,7 @@ public static bool IsLeapYear(this short value)
             value++;
         }
 
-        return value.Mod(4) == 0 && (value.Mod(100) != 0 || value.Mod(400) == 0);
+        return value.Mod((short)4) == 0 && (value.Mod((short)100) != 0 || value.Mod((short)400) == 0);
     }
 
     /// <summary>

X10D/src/Time/SByteExtensions.cs

@@ -33,7 +33,7 @@ public static bool IsLeapYear(this sbyte value)
             value++;
         }
 
-        return value.Mod(4) == 0 && value.Mod(100) != 0; // mod 400 not required, sbyte.MaxValue is 127 anyway
+        return value.Mod((sbyte)4) == 0 && value.Mod((sbyte)100) != 0; // mod 400 not required, sbyte.MaxValue is 127 anyway
     }
 
     /// <summary>