Avoid some allocations around MPInteger

1 files changed, 36 insertions, 29 deletions

diff --git a/crypto/src/bcpg/MPInteger.cs b/crypto/src/bcpg/MPInteger.cs
index 441407244..2f564b00c 100644
--- a/crypto/src/bcpg/MPInteger.cs
+++ b/crypto/src/bcpg/MPInteger.cs
@@ -1,59 +1,66 @@
 using System;
-using System.IO;
 
 using Org.BouncyCastle.Math;
+using Org.BouncyCastle.Math.EC;
 
 namespace Org.BouncyCastle.Bcpg
 {
 	/// <remarks>A multiple precision integer</remarks>
-    public class MPInteger
+    public sealed class MPInteger
         : BcpgObject
     {
-        private readonly BigInteger val;
+        private readonly BigInteger m_val;
 
-        public MPInteger(
-            BcpgInputStream bcpgIn)
+        public MPInteger(BcpgInputStream bcpgIn)
         {
 			if (bcpgIn == null)
-				throw new ArgumentNullException("bcpgIn");
+				throw new ArgumentNullException(nameof(bcpgIn));
 
-			int length = (bcpgIn.ReadByte() << 8) | bcpgIn.ReadByte();
-            byte[] bytes = new byte[(length + 7) / 8];
+			int lengthInBits = (bcpgIn.ReadByte() << 8) | bcpgIn.ReadByte();
+            int lengthInBytes = (lengthInBits + 7) / 8;
 
-            bcpgIn.ReadFully(bytes);
+#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+            if (lengthInBytes <= 512)
+            {
+                Span<byte> span = stackalloc byte[lengthInBytes];
+                bcpgIn.ReadFully(span);
+                m_val = new BigInteger(1, span);
+                return;
+            }
+#endif
 
-            this.val = new BigInteger(1, bytes);
+            byte[] bytes = new byte[lengthInBytes];
+            bcpgIn.ReadFully(bytes);
+            m_val = new BigInteger(1, bytes);
         }
 
-		public MPInteger(
-            BigInteger val)
+		public MPInteger(BigInteger val)
         {
 			if (val == null)
-				throw new ArgumentNullException("val");
+				throw new ArgumentNullException(nameof(val));
 			if (val.SignValue < 0)
-				throw new ArgumentException("Values must be positive", "val");
+				throw new ArgumentException("Values must be positive", nameof(val));
 
-			this.val = val;
+			m_val = val;
         }
 
-		public BigInteger Value
+        public BigInteger Value => m_val;
+
+        public override void Encode(BcpgOutputStream bcpgOut)
         {
-            get { return val; }
+            bcpgOut.WriteShort((short)m_val.BitLength);
+            bcpgOut.Write(m_val.ToByteArrayUnsigned());
         }
 
-        public override void Encode(
-            BcpgOutputStream bcpgOut)
+        internal static BigInteger ToMpiBigInteger(ECPoint point)
         {
-			bcpgOut.WriteShort((short) val.BitLength);
-			bcpgOut.Write(val.ToByteArrayUnsigned());
+#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
+            Span<byte> encoding = stackalloc byte[point.GetEncodedLength(false)];
+            point.EncodeTo(false, encoding);
+            return new BigInteger(1, encoding);
+#else
+            return new BigInteger(1, point.GetEncoded(false));
+#endif
         }
-
-		internal static void Encode(
-			BcpgOutputStream	bcpgOut,
-			BigInteger			val)
-		{
-			bcpgOut.WriteShort((short) val.BitLength);
-			bcpgOut.Write(val.ToByteArrayUnsigned());
-		}
     }
 }