From 2b924524ecd58e7973f8df45df1c1d10f41526dc Mon Sep 17 00:00:00 2001
From: Leo Yuriev <leo@yuriev.ru>
Date: Wed, 15 Feb 2017 20:16:07 +0300
Subject: [PATCH] mdbx: initial mdbx_cursor_on_ first/last().

---
 mdbx.c | 41 +++++++++++++++++++++++++++++++++++++++++
 mdbx.h | 13 +++++++++++--
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/mdbx.c b/mdbx.c
index 3599d14b..d32394a5 100644
--- a/mdbx.c
+++ b/mdbx.c
@@ -354,6 +354,47 @@ size_t mdbx_canary_get(MDB_txn *txn, mdbx_canary* canary)
 	return txn->mt_txnid;
 }
 
+int mdbx_cursor_on_first(MDB_cursor *mc)
+{
+	if (unlikely(mc == NULL))
+		return EINVAL;
+
+	if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
+		return MDB_VERSION_MISMATCH;
+
+	if (!(mc->mc_flags & C_INITIALIZED))
+		return MDBX_RESULT_FALSE;
+
+	unsigned i;
+	for(i = 0; i < mc->mc_snum; ++i) {
+		if (mc->mc_ki[i])
+			return MDBX_RESULT_FALSE;
+		}
+
+	return MDBX_RESULT_TRUE;
+}
+
+int mdbx_cursor_on_last(MDB_cursor *mc)
+{
+	if (unlikely(mc == NULL))
+		return EINVAL;
+
+	if (unlikely(mc->mc_signature != MDBX_MC_SIGNATURE))
+		return MDB_VERSION_MISMATCH;
+
+	if (!(mc->mc_flags & C_INITIALIZED))
+		return MDBX_RESULT_FALSE;
+
+	unsigned i;
+	for(i = 0; i < mc->mc_snum; ++i) {
+		unsigned nkeys = NUMKEYS(mc->mc_pg[i]);
+		if (mc->mc_ki[i] != nkeys - 1)
+			return MDBX_RESULT_FALSE;
+	}
+
+	return MDBX_RESULT_TRUE;
+}
+
 int mdbx_cursor_eof(MDB_cursor *mc)
 {
 	if (unlikely(mc == NULL))
diff --git a/mdbx.h b/mdbx.h
index 6a266395..515e819e 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -219,10 +219,19 @@ typedef struct mdbx_canary {
 int mdbx_canary_put(MDB_txn *txn, const mdbx_canary* canary);
 size_t mdbx_canary_get(MDB_txn *txn, mdbx_canary* canary);
 
-/* Returns 1 when no more data available or cursor not positioned,
- * 0 otherwise or less that zero in error case. */
+/* Returns:
+ *	- MDBX_RESULT_TRUE	when no more data available
+ *				or cursor not positioned;
+ *	- MDBX_RESULT_FALSE	when data available;
+ *	- Otherwise the error code. */
 int mdbx_cursor_eof(MDB_cursor *mc);
 
+/* Returns: MDBX_RESULT_TRUE, MDBX_RESULT_FALSE or Error code. */
+int mdbx_cursor_on_first(MDB_cursor *mc);
+
+/* Returns: MDBX_RESULT_TRUE, MDBX_RESULT_FALSE or Error code. */
+int mdbx_cursor_on_last(MDB_cursor *mc);
+
 #define MDBX_EMULTIVAL (MDB_LAST_ERRCODE - 42)
 #define MDBX_RESULT_FALSE MDB_SUCCESS
 #define MDBX_RESULT_TRUE (-1)