From aca3754a17de70453dd51d94b86dea54ae1b221b Mon Sep 17 00:00:00 2001
From: Joseph Da Silva <39675835+jfd16@users.noreply.github.com>
Date: Sat, 26 Jun 2021 12:33:01 -0700
Subject: [PATCH] Fix BigInteger hex string parsing bug (#54251) (#54262)

---
 .../src/System/Numerics/BigNumber.cs                        |  2 +-
 .../System.Runtime.Numerics/tests/BigInteger/parse.cs       | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
index 957bd73..5ce7919 100644
--- a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
+++ b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs
@@ -467,8 +467,8 @@ namespace System.Numerics
 
                     if ((!isNegative && sign < 0) || sign == int.MinValue)
                     {
-                        sign = isNegative ? -1 : 1;
                         bits = new[] { (uint)sign };
+                        sign = isNegative ? -1 : 1;
                     }
                 }
                 else
diff --git a/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs b/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
index 23440b4..115a613 100644
--- a/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
+++ b/src/libraries/System.Runtime.Numerics/tests/BigInteger/parse.cs
@@ -105,6 +105,19 @@ namespace System.Numerics.Tests
             Assert.Equal(0, result);
         }
 
+        [Fact]
+        public void Parse_Hex32Bits()
+        {
+            // Regression test for: https://github.com/dotnet/runtime/issues/54251
+            BigInteger result;
+
+            Assert.True(BigInteger.TryParse("80000000", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(int.MinValue, result);
+
+            Assert.True(BigInteger.TryParse("080000001", NumberStyles.HexNumber, null, out result));
+            Assert.Equal(0x80000001u, result);
+        }
+
         private static void RunFormatProviderParseStrings()
         {
             NumberFormatInfo nfi = new NumberFormatInfo();
-- 
2.7.4