diff --git a/crypto/src/util/BigIntegers.cs b/crypto/src/util/BigIntegers.cs
index 6674750bb..bac5f12c0 100644
--- a/crypto/src/util/BigIntegers.cs
+++ b/crypto/src/util/BigIntegers.cs
@@ -15,7 +15,7 @@ namespace Org.BouncyCastle.Utilities
/**
* Return the passed in value as an unsigned byte array.
*
- * @param value value to be converted.
+ * @param value the value to be converted.
* @return a byte array without a leading zero byte if present in the signed encoding.
*/
public static byte[] AsUnsignedByteArray(
@@ -25,11 +25,11 @@ namespace Org.BouncyCastle.Utilities
}
/**
- * Return the passed in value as an unsigned byte array of specified length, zero-extended as necessary.
- *
- * @param length desired length of result array.
- * @param n value to be converted.
- * @return a byte array of specified length, with leading zeroes as necessary given the size of n.
+ * Return the passed in value as an unsigned byte array of the specified length, padded with
+ * leading zeros as necessary.
+ * @param length the fixed length of the result.
+ * @param n the value to be converted.
+ * @return a byte array padded to a fixed length with leading zeros.
*/
public static byte[] AsUnsignedByteArray(int length, BigInteger n)
{
@@ -46,6 +46,39 @@ namespace Org.BouncyCastle.Utilities
return tmp;
}
+ /**
+ * Write the passed in value as unsigned bytes to the specified buffer range, padded with
+ * leading zeros as necessary.
+ *
+ * @param value
+ * the value to be converted.
+ * @param buf
+ * the buffer to which the value is written.
+ * @param off
+ * the start offset in array <code>buf</code> at which the data is written.
+ * @param len
+ * the fixed length of data written (possibly padded with leading zeros).
+ */
+ public static void AsUnsignedByteArray(BigInteger value, byte[] buf, int off, int len)
+ {
+ byte[] bytes = value.ToByteArrayUnsigned();
+ if (bytes.Length == len)
+ {
+ Array.Copy(bytes, 0, buf, off, len);
+ return;
+ }
+
+ int start = bytes[0] == 0 ? 1 : 0;
+ int count = bytes.Length - start;
+
+ if (count > len)
+ throw new ArgumentException("standard length exceeded for value");
+
+ int padLen = len - count;
+ Arrays.Fill(buf, off, off + padLen, 0);
+ Array.Copy(bytes, start, buf, off + padLen, count);
+ }
+
/// <summary>
/// Creates a Random BigInteger from the secure random of a given bit length.
/// </summary>
diff --git a/crypto/src/util/Integers.cs b/crypto/src/util/Integers.cs
index bd05a053e..afb4b827f 100644
--- a/crypto/src/util/Integers.cs
+++ b/crypto/src/util/Integers.cs
@@ -19,6 +19,20 @@ namespace Org.BouncyCastle.Utilities
return n;
}
+ public static int NumberOfTrailingZeros(int i)
+ {
+ if (i == 0)
+ return 32;
+
+ int count = 0;
+ while ((i & 1) == 0)
+ {
+ i >>= 1;
+ ++count;
+ }
+ return count;
+ }
+
public static int RotateLeft(int i, int distance)
{
return (i << distance) ^ (int)((uint)i >> -distance);
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