WIP: add AllBitsSet to BigInteger with the wrong DIM, add test case.

Author: dakersnar

src/libraries/Common/tests/System/GenericMathHelpers.cs

@@ -59,6 +59,8 @@ public static class BinaryIntegerHelper<TSelf>
     public static class BinaryNumberHelper<TSelf>
         where TSelf : IBinaryNumber<TSelf>
     {
+        public static TSelf AllBitsSet => TSelf.AllBitsSet;
+
         public static bool IsPow2(TSelf value) => TSelf.IsPow2(value);
 
         public static TSelf Log2(TSelf value) => TSelf.Log2(value);

src/libraries/System.Private.CoreLib/src/System/Numerics/IBinaryNumber.cs

@@ -10,6 +10,9 @@ public interface IBinaryNumber<TSelf>
           INumber<TSelf>
         where TSelf : IBinaryNumber<TSelf>
     {
+        /// <summary>Gets an instance of the binary type in which all bits are set.</summary>
+        static virtual TSelf AllBitsSet => TSelf.One; // TODO: add the correct DIM when I am confident everything works
+
         /// <summary>Determines if a value is a power of two.</summary>
         /// <param name="value">The value to be checked.</param>
         /// <returns><c>true</c> if <paramref name="value" /> is a power of two; otherwise, <c>false</c>.</returns>

src/libraries/System.Runtime.Numerics/ref/System.Runtime.Numerics.cs

@@ -60,6 +60,7 @@ namespace System.Numerics
         public static bool IsNegative(System.Numerics.BigInteger value) { throw null; }
         public static bool IsOddInteger(System.Numerics.BigInteger value) { throw null; }
         public static bool IsPositive(System.Numerics.BigInteger value) { throw null; }
+        static BigInteger System.Numerics.IBinaryNumber<BigInteger>.AllBitsSet { get { throw null; } }
         public static bool IsPow2(System.Numerics.BigInteger value) { throw null; }
         public static System.Numerics.BigInteger LeadingZeroCount(System.Numerics.BigInteger value) { throw null; }
         public static double Log(System.Numerics.BigInteger value) { throw null; }

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs

@@ -3821,6 +3821,9 @@ private int GetGenericMathByteCount()
         // IBinaryNumber
         //
 
+        /// <inheritdoc cref="IBinaryNumber{TSelf}.AllBitsSet" />
+        static BigInteger IBinaryNumber<BigInteger>.AllBitsSet => MinusOne;
+
         /// <inheritdoc cref="IBinaryNumber{TSelf}.IsPow2(TSelf)" />
         public static bool IsPow2(BigInteger value) => value.IsPowerOfTwo;
 

src/libraries/System.Runtime.Numerics/tests/BigIntegerTests.GenericMath.cs

@@ -550,6 +550,12 @@ public static void TryWriteLittleEndianTest()
         // IBinaryNumber
         //
 
+        [Fact]
+        public static void AllBitsSetTest()
+        {
+            Assert.Equal(NegativeOne, BinaryNumberHelper<BigInteger>.AllBitsSet);
+        }
+
         [Fact]
         public static void IsPow2Test()
         {

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -10382,6 +10382,7 @@ public partial interface IBinaryInteger<TSelf> : System.IComparable, System.ICom
     }
     public partial interface IBinaryNumber<TSelf> : System.IComparable, System.IComparable<TSelf>, System.IEquatable<TSelf>, System.IFormattable, System.IParsable<TSelf>, System.ISpanFormattable, System.ISpanParsable<TSelf>, System.Numerics.IAdditionOperators<TSelf, TSelf, TSelf>, System.Numerics.IAdditiveIdentity<TSelf, TSelf>, System.Numerics.IBitwiseOperators<TSelf, TSelf, TSelf>, System.Numerics.IComparisonOperators<TSelf, TSelf>, System.Numerics.IDecrementOperators<TSelf>, System.Numerics.IDivisionOperators<TSelf, TSelf, TSelf>, System.Numerics.IEqualityOperators<TSelf, TSelf>, System.Numerics.IIncrementOperators<TSelf>, System.Numerics.IModulusOperators<TSelf, TSelf, TSelf>, System.Numerics.IMultiplicativeIdentity<TSelf, TSelf>, System.Numerics.IMultiplyOperators<TSelf, TSelf, TSelf>, System.Numerics.INumber<TSelf>, System.Numerics.INumberBase<TSelf>, System.Numerics.ISubtractionOperators<TSelf, TSelf, TSelf>, System.Numerics.IUnaryNegationOperators<TSelf, TSelf>, System.Numerics.IUnaryPlusOperators<TSelf, TSelf> where TSelf : System.Numerics.IBinaryNumber<TSelf>
     {
+        static virtual TSelf AllBitsSet => throw null;
         static abstract bool IsPow2(TSelf value);
         static abstract TSelf Log2(TSelf value);
     }