Add extra arg to addWord() and add variant of copy()

2 files changed, 13 insertions, 7 deletions

diff --git a/core/src/main/java/org/bouncycastle/math/ec/Nat.java b/core/src/main/java/org/bouncycastle/math/ec/Nat.java
index 40b6ebb3..2cf00c59 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/Nat.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/Nat.java
@@ -70,18 +70,19 @@ public abstract class Nat
         return (int)c;
     }
 
-    public static int addWord(int len, int x, int[] z)
+    public static int addWord(int len, int x, int[] z, int zOff)
     {
-        long c = (x & M) + (z[0] & M);
-        z[0] = (int)c;
+        // assert zOff < len;
+        long c = (x & M) + (z[zOff + 0] & M);
+        z[zOff + 0] = (int)c;
         c >>>= 32;
-        return c == 0 ? 0 : inc(len, z, 1);
+        return c == 0 ? 0 : inc(len, z, zOff + 1);
     }
 
     public static int addWordExt(int len, int x, int[] zz, int zzOff)
     {
         int extLen = len << 1;
-        // assert zzOff <= (extLen - 1);
+        // assert zzOff < extLen;
         long c = (x & M) + (zz[zzOff + 0] & M);
         zz[zzOff + 0] = (int)c;
         c >>>= 32;
@@ -95,6 +96,11 @@ public abstract class Nat
         return z;
     }
 
+    public static void copy(int len, int[] x, int[] z)
+    {
+        System.arraycopy(x, 0, z, 0, len);
+    }
+
     public static int[] create(int len)
     {
         return new int[len];
diff --git a/core/src/main/java/org/bouncycastle/math/ec/custom/sec/SecP521R1Field.java b/core/src/main/java/org/bouncycastle/math/ec/custom/sec/SecP521R1Field.java
index 5d0a0fd7..1608d406 100644
--- a/core/src/main/java/org/bouncycastle/math/ec/custom/sec/SecP521R1Field.java
+++ b/core/src/main/java/org/bouncycastle/math/ec/custom/sec/SecP521R1Field.java
@@ -24,7 +24,7 @@ public class SecP521R1Field
 
     public static void addOne(int[] x, int[] z)
     {
-        System.arraycopy(x, 0, z, 0, 16);
+        Nat.copy(16, x, z);
         int c = Nat.inc(16, z, 0) + x[16];
         if (c > P16 || (c == P16 && Nat.eq(16, z, P)))
         {
@@ -89,7 +89,7 @@ public class SecP521R1Field
     public static void reduce23(int[] z)
     {
         int z16 = z[16];
-        int c = Nat.addWord(16, z16 >>> 9, z) + (z16 & P16);
+        int 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);