mdbx: добавление mdbx_cursor_on_first/last_dup() в API.

mdbx.h

@@ -5138,6 +5138,10 @@ mdbx_cursor_eof(const MDBX_cursor *cursor);
 MDBX_NOTHROW_PURE_FUNCTION LIBMDBX_API int
 mdbx_cursor_on_first(const MDBX_cursor *cursor);
 
+/** FIXME */
+MDBX_NOTHROW_PURE_FUNCTION LIBMDBX_API int
+mdbx_cursor_on_first_dup(const MDBX_cursor *cursor);
+
 /** \brief Determines whether the cursor is pointed to the last key-value pair
  * or not.
  * \ingroup c_cursors
@@ -5152,6 +5156,10 @@ mdbx_cursor_on_first(const MDBX_cursor *cursor);
 MDBX_NOTHROW_PURE_FUNCTION LIBMDBX_API int
 mdbx_cursor_on_last(const MDBX_cursor *cursor);
 
+/** FIXME */
+MDBX_NOTHROW_PURE_FUNCTION LIBMDBX_API int
+mdbx_cursor_on_last_dup(const MDBX_cursor *cursor);
+
 /** \addtogroup c_rqest
  * \details \note The estimation result varies greatly depending on the filling
  * of specific pages and the overall balance of the b-tree:

mdbx.h++

@@ -4467,6 +4467,8 @@ public:
   inline bool eof() const;
   inline bool on_first() const;
   inline bool on_last() const;
+  inline bool on_first_multival() const;
+  inline bool on_last_multival() const;
   inline estimate_result estimate(const slice &key, const slice &value) const;
   inline estimate_result estimate(const slice &key) const;
   inline estimate_result estimate(move_operation operation) const;
@@ -6396,6 +6398,14 @@ inline bool cursor::on_last() const {
   return error::boolean_or_throw(::mdbx_cursor_on_last(*this));
 }
 
+inline bool cursor::on_first_multival() const {
+  return error::boolean_or_throw(::mdbx_cursor_on_first_dup(*this));
+}
+
+inline bool cursor::on_last_multival() const {
+  return error::boolean_or_throw(::mdbx_cursor_on_last_dup(*this));
+}
+
 inline cursor::estimate_result cursor::estimate(const slice &key,
                                                 const slice &value) const {
   return estimate_result(*this, multi_exactkey_lowerboundvalue, key, value);

src/core.c

@@ -24533,6 +24533,29 @@ int mdbx_cursor_on_first(const MDBX_cursor *mc) {
   return MDBX_RESULT_TRUE;
 }
 
+int mdbx_cursor_on_first_dup(const MDBX_cursor *mc) {
+  if (unlikely(mc == NULL))
+    return MDBX_EINVAL;
+
+  if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
+    return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
+                                                     : MDBX_EBADSIGN;
+
+  if (!(mc->mc_flags & C_INITIALIZED))
+    return mc->mc_db->md_entries ? MDBX_RESULT_FALSE : MDBX_RESULT_TRUE;
+
+  if (!mc->mc_xcursor)
+    return MDBX_RESULT_TRUE;
+
+  mc = &mc->mc_xcursor->mx_cursor;
+  for (size_t 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(const MDBX_cursor *mc) {
   if (unlikely(mc == NULL))
     return MDBX_EINVAL;
@@ -24553,6 +24576,30 @@ int mdbx_cursor_on_last(const MDBX_cursor *mc) {
   return MDBX_RESULT_TRUE;
 }
 
+int mdbx_cursor_on_last_dup(const MDBX_cursor *mc) {
+  if (unlikely(mc == NULL))
+    return MDBX_EINVAL;
+
+  if (unlikely(mc->mc_signature != MDBX_MC_LIVE))
+    return (mc->mc_signature == MDBX_MC_READY4CLOSE) ? MDBX_EINVAL
+                                                     : MDBX_EBADSIGN;
+
+  if (!(mc->mc_flags & C_INITIALIZED))
+    return mc->mc_db->md_entries ? MDBX_RESULT_FALSE : MDBX_RESULT_TRUE;
+
+  if (!mc->mc_xcursor)
+    return MDBX_RESULT_TRUE;
+
+  mc = &mc->mc_xcursor->mx_cursor;
+  for (size_t i = 0; i < mc->mc_snum; ++i) {
+    size_t nkeys = page_numkeys(mc->mc_pg[i]);
+    if (mc->mc_ki[i] < nkeys - 1)
+      return MDBX_RESULT_FALSE;
+  }
+
+  return MDBX_RESULT_TRUE;
+}
+
 int mdbx_cursor_eof(const MDBX_cursor *mc) {
   if (unlikely(mc == NULL))
     return MDBX_EINVAL;