Fix final step of Reduce()

1 files changed, 9 insertions, 10 deletions

diff --git a/crypto/src/math/ec/custom/sec/SecP256R1Field.cs b/crypto/src/math/ec/custom/sec/SecP256R1Field.cs

index cb9874bfd..eab4af956 100644
--- a/crypto/src/math/ec/custom/sec/SecP256R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP256R1Field.cs
@@ -115,27 +115,26 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
             cc >>= 32;
 
             int c = (int)cc;
-            if (c > 0)
+            if (c < 0)
             {
                 do
                 {
+                    c += (int)Nat256.Add(z, P, z);
+                }
+                while (c < 0);
+            }
+            else
+            {
+                while (c > 0)
+                {
                     c += Nat256.Sub(z, P, z);
                 }
-                while (c != 0);
 
                 if (z[7] == P7 && Nat256.Gte(z, P))
                 {
                     Nat256.Sub(z, P, z);
                 }
             }
-            else if (c < 0)
-            {
-                do
-                {
-                    c += (int)Nat256.Add(z, P, z);
-                }
-                while (c != 0);
-            }
         }
 
         public static void Square(uint[] x, uint[] z)