Introduce ObjectId.StartsWith()

1 files changed, 47 insertions, 0 deletions

diff --git a/LibGit2Sharp/ObjectId.cs b/LibGit2Sharp/ObjectId.cs
index f3bb0481..3818347e 100644
--- a/LibGit2Sharp/ObjectId.cs
+++ b/LibGit2Sharp/ObjectId.cs
@@ -297,5 +297,52 @@ namespace LibGit2Sharp
 
             return objectId.All(c => hexDigits.Contains(c.ToString(CultureInfo.InvariantCulture)));
         }
+
+        /// <summary>
+        /// Determine whether the beginning of this instance matches the
+        /// <paramref name="len"/> first nibbles of <paramref name="rawId"/>.
+        /// </summary>
+        /// <param name="rawId">The byte array to compare the <see cref="ObjectId"/> against.</param>
+        /// <param name="len">The number of nibbles from <paramref name="rawId"/> </param>
+        /// <returns></returns>
+        public bool StartsWith(byte[] rawId, int len)
+        {
+            Ensure.ArgumentNotNull(rawId, "rawId");
+
+            if (len < 1 || len > HexSize)
+            {
+                throw new ArgumentOutOfRangeException("len");
+            }
+
+            if (len > rawId.Length * 2)
+            {
+                throw new ArgumentOutOfRangeException("len", "len exceeds the size of rawId");
+            }
+
+            bool match = true;
+
+            int length = len >> 1;
+            for (int i = 0; i < length; i++)
+            {
+                if (RawId[i] != rawId[i])
+                {
+                    match = false;
+                    break;
+                }
+            }
+
+            if (match && ((len & 1) == 1))
+            {
+                var a = RawId[length] >> 4;
+                var b = rawId[length] >> 4;
+
+                if (a != b)
+                {
+                    match = false;
+                }
+            }
+
+            return match;
+        }
     }
 }