Add extra arg to AddWord() and add variant of Copy()

2 files changed, 12 insertions, 6 deletions

diff --git a/crypto/src/math/ec/Nat.cs b/crypto/src/math/ec/Nat.cs

index a5a496fad..9d2290ba7 100644
--- a/crypto/src/math/ec/Nat.cs
+++ b/crypto/src/math/ec/Nat.cs
@@ -69,10 +69,11 @@ namespace Org.BouncyCastle.Math.EC
             return (uint)c;
         }
 
-        public static uint AddWord(int len, uint x, uint[] z)
+        public static uint AddWord(int len, uint x, uint[] z, int zOff)
         {
-            ulong c = (ulong)x + z[0];
-            z[0] = (uint)c;
+            Debug.Assert(zOff < len);
+            ulong c = (ulong)x + z[zOff + 0];
+            z[zOff + 0] = (uint)c;
             c >>= 32;
             return c == 0 ? 0 : Inc(len, z, 1);
         }
@@ -80,13 +81,18 @@ namespace Org.BouncyCastle.Math.EC
         public static uint AddWordExt(int len, uint x, uint[] zz, int zzOff)
         {
             int extLen = len << 1;
-            Debug.Assert(zzOff <= (extLen - 1));
+            Debug.Assert(zzOff < extLen);
             ulong c = (ulong)x + zz[zzOff];
             zz[zzOff] = (uint)c;
             c >>= 32;
             return c == 0 ? 0 : Inc(extLen, zz, zzOff + 1);
         }
 
+        public static void Copy(int len, uint[] x, uint[] z)
+        {
+            Array.Copy(x, 0, z, 0, len);
+        }
+
         public static uint[] Copy(int len, uint[] x)
         {
             uint[] z = new uint[len];
diff --git a/crypto/src/math/ec/custom/sec/SecP521R1Field.cs b/crypto/src/math/ec/custom/sec/SecP521R1Field.cs

index cfe3202cd..f57804778 100644
--- a/crypto/src/math/ec/custom/sec/SecP521R1Field.cs
+++ b/crypto/src/math/ec/custom/sec/SecP521R1Field.cs
@@ -23,7 +23,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
 
         public static void AddOne(uint[] x, uint[] z)
         {
-            Array.Copy(x, 0, z, 0, 16);
+            Nat.Copy(16, x, z);
             uint c = Nat.Inc(16, z, 0) + x[16];
             if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
             {
@@ -87,7 +87,7 @@ namespace Org.BouncyCastle.Math.EC.Custom.Sec
         public static void Reduce23(uint[] z)
         {
             uint z16 = z[16];
-            uint c = Nat.AddWord(16, z16 >> 9, z) + (z16 & P16);
+            uint c = Nat.AddWord(16, z16 >> 9, z, 0) + (z16 & P16);
             if (c > P16 || (c == P16 && Nat.Eq(16, z, P)))
             {
                 c += Nat.Inc(16, z, 0);