Fix BigInteger parse hex strings on negative numbers (#84792)

fixes #74758
dotnet · May 10, 2023 · 40438e0 · 40438e0
1 parent c77d916
commit 40438e0
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Showing 2 changed files with 12 additions and 13 deletions.
diff --git a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
@@ -466,6 +466,11 @@ private static ParsingStatus HexNumberToBigInteger(ref BigNumberBuffer number, o
 
                 Debug.Assert(partialDigitCount == 0 && bitsBufferPos == -1);
 
+                if (isNegative)
+                {
+                    NumericsHelpers.DangerousMakeTwosComplement(bitsBuffer);
+                }
+
                 // BigInteger requires leading zero blocks to be truncated.
                 bitsBuffer = bitsBuffer.TrimEnd(0u);
 
@@ -477,26 +482,15 @@ private static ParsingStatus HexNumberToBigInteger(ref BigNumberBuffer number, o
                     sign = 0;
                     bits = null;
                 }
-                else if (bitsBuffer.Length == 1)
+                else if (bitsBuffer.Length == 1 && bitsBuffer[0] <= int.MaxValue)
                 {
-                    sign = (int)bitsBuffer[0];
+                    sign = (int)bitsBuffer[0] * (isNegative ? -1 : 1);
                     bits = null;
-
-                    if ((!isNegative && sign < 0) || sign == int.MinValue)
-                    {
-                        bits = new[] { (uint)sign };
-                        sign = isNegative ? -1 : 1;
-                    }
                 }
                 else
                 {
                     sign = isNegative ? -1 : 1;
                     bits = bitsBuffer.ToArray();
-
-                    if (isNegative)
-                    {
-                        NumericsHelpers.DangerousMakeTwosComplement(bits);
-                    }
                 }
 
                 result = new BigInteger(sign, bits);

diff --git a/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs b/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
@@ -132,6 +132,11 @@ public void Parse_Hex32Bits()
             Assert.True(BigInteger.TryParse("080000001", NumberStyles.HexNumber, null, out result));
             Assert.Equal(0x80000001u, 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);
+            Assert.Equal(-2, result);
+
             Assert.Throws<FormatException>(() =>
             {
                 BigInteger.Parse("zzz", NumberStyles.HexNumber);