Fix TryParseBigIntegerHexOrBinaryNumberStyle (#97995)

* Fix TryParseBigIntegerHexOrBinaryNumberStyle

* Fix typo

* Add hex test

---------

Co-authored-by: Tanner Gooding <[email protected]>

Author: kzrnm

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

@@ -445,7 +445,7 @@ internal static ParsingStatus TryParseBigIntegerHexOrBinaryNumberStyle<TParser,
             int leadingBitsCount = value.Length % TParser.DigitsPerBlock;
 
             uint leading = signBits;
-            // First parse unanligned leading block if exists.
+            // First parse unaligned leading block if exists.
             if (leadingBitsCount != 0)
             {
                 if (!TParser.TryParseUnalignedBlock(value[0..leadingBitsCount], out leading))
@@ -484,8 +484,8 @@ internal static ParsingStatus TryParseBigIntegerHexOrBinaryNumberStyle<TParser,
                     // Require to store in _bits.
 
                     // Positive: sign=1, bits=[leading]
-                    // Negative: sign=-1, bits=[leading ^ -1 + 1]=[-leading]
-                    result = new BigInteger((int)signBits | 1, [leading ^ signBits - signBits]);
+                    // Negative: sign=-1, bits=[(leading ^ -1) + 1]=[-leading]
+                    result = new BigInteger((int)signBits | 1, [(leading ^ signBits) - signBits]);
                     return ParsingStatus.OK;
                 }
                 else

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

@@ -143,6 +143,18 @@ public void Parse_Hex32Bits()
             Assert.True(BigInteger.TryParse("080000001", NumberStyles.HexNumber, null, out result));
             Assert.Equal(0x80000001u, result);
 
+            Assert.True(BigInteger.TryParse("F0000001", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(-0xFFFFFFFL, result);
+
+            Assert.True(BigInteger.TryParse("0F0000001", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(0xF0000001u, result);
+            
+            Assert.True(BigInteger.TryParse("F00000001", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(-0xFFFFFFFFL, result);
+
+            Assert.True(BigInteger.TryParse("0F00000001", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(0xF00000001u, result);
+
             // Regression test for: https://github.com/dotnet/runtime/issues/74758
             Assert.True(BigInteger.TryParse("FFFFFFFFE", NumberStyles.HexNumber, null, out result));
             Assert.Equal(new BigInteger(-2), result);
@@ -175,6 +187,7 @@ public void Parse_Hex32Bits()
         [InlineData("10000000000000000000000000000000", (long)int.MinValue)]
         [InlineData("010000000000000000000000000000001", 0x080000001L)]
         [InlineData("111111111111111111111111111111110", -2L)]
+        [InlineData("100000000000000000000000000000001", -0xFFFFFFFFL)]
         [InlineData("0111111111111111111111111111111111", 0x1FFFFFFFFL)]
         public void Parse_BinSpecialCases(string input, long expectedValue)
         {