Fix some generic math DIMs to have the correct behavior

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

@@ -37,7 +37,7 @@ static virtual TSelf LeadingZeroCount(TSelf value)
                 return TSelf.CreateChecked(bitCount);
             }
 
-            return (bitCount - TSelf.One) ^ TSelf.Log2(value);
+            return TSelf.IsNegative(value) ? TSelf.Zero : ((bitCount - TSelf.One) ^ TSelf.Log2(value));
         }
 
         /// <summary>Computes the number of bits that are set in a value.</summary>

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

@@ -118,9 +118,14 @@ static virtual TSelf Min(TSelf x, TSelf y)
             // otherwise returns the larger of the inputs. It
             // treats +0 as larger than -0 as per the specification.
 
-            if ((x != y) && !TSelf.IsNaN(x))
+            if (x != y)
             {
-                return x < y ? x : y;
+                if (!TSelf.IsNaN(x))
+                {
+                    return x < y ? x : y;
+                }
+
+                return x;
             }
 
             return TSelf.IsNegative(x) ? x : y;
@@ -160,6 +165,10 @@ static virtual int Sign(TSelf value)
         {
             if (value != TSelf.Zero)
             {
+                if (TSelf.IsNaN(value))
+                {
+                    ThrowHelper.ThrowArithmeticException(SR.Arithmetic_NaN);
+                }
                 return TSelf.IsNegative(value) ? -1 : +1;
             }
             return 0;

src/libraries/System.Private.CoreLib/src/System/ThrowHelper.cs

@@ -53,6 +53,12 @@ namespace System
     [StackTraceHidden]
     internal static class ThrowHelper
     {
+        [DoesNotReturn]
+        internal static void ThrowArithmeticException(string message)
+        {
+            throw new ArithmeticException(message);
+        }
+
         [DoesNotReturn]
         internal static void ThrowAccessViolationException()
         {