From 5cf6542fa002a1cd543ac524b5bfb8de43e00337 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=9B=D0=B5=D0=BE=D0=BD=D0=B8=D0=B4=20=D0=AE=D1=80=D1=8C?=
 =?UTF-8?q?=D0=B5=D0=B2=20=28Leonid=20Yuriev=29?= <leo@yuriev.ru>
Date: Sat, 18 Nov 2023 23:20:53 +0300
Subject: [PATCH] =?UTF-8?q?mdbx:=20=D0=B4=D0=BE=D0=B1=D0=B0=D0=B2=D0=BB?=
 =?UTF-8?q?=D0=B5=D0=BD=D0=B8=D0=B5=20`mdbx=5Fcursor=5Fscan=5Ffrom()`=20?=
 =?UTF-8?q?=D0=B2=20API.?=
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---
 mdbx.h     |  7 +++++++
 src/core.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/mdbx.h b/mdbx.h
index c1fdd90e..611efd1e 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -4938,6 +4938,13 @@ LIBMDBX_API int mdbx_cursor_scan(MDBX_cursor *cursor,
                                  MDBX_cursor_op start_op,
                                  MDBX_cursor_op turn_op, void *arg);
 
+/** FIXME */
+LIBMDBX_API int mdbx_cursor_scan_from(MDBX_cursor *cursor,
+                                      MDBX_predicate_func *predicate,
+                                      void *context, MDBX_cursor_op from_op,
+                                      MDBX_val *from_key, MDBX_val *from_value,
+                                      MDBX_cursor_op turn_op, void *arg);
+
 /** \brief Retrieve multiple non-dupsort key/value pairs by cursor.
  * \ingroup c_crud
  *
diff --git a/src/core.c b/src/core.c
index 23eaaa92..861c266f 100644
--- a/src/core.c
+++ b/src/core.c
@@ -17466,6 +17466,50 @@ int mdbx_cursor_scan(MDBX_cursor *mc, MDBX_predicate_func *predicate,
   }
 }
 
+int mdbx_cursor_scan_from(MDBX_cursor *mc, MDBX_predicate_func *predicate,
+                          void *context, MDBX_cursor_op from_op, MDBX_val *key,
+                          MDBX_val *value, MDBX_cursor_op turn_op, void *arg) {
+  if (unlikely(!predicate))
+    return MDBX_EINVAL;
+
+  const unsigned valid_start_mask =
+      1 << MDBX_GET_BOTH | 1 << MDBX_GET_BOTH_RANGE | 1 << MDBX_SET_KEY |
+      1 << MDBX_GET_MULTIPLE | 1 << MDBX_SET_LOWERBOUND |
+      1 << MDBX_SET_UPPERBOUND;
+  ;
+  if (unlikely(from_op < MDBX_TO_KEY_LESSER_THAN &&
+               ((1 << from_op) & valid_start_mask) == 0))
+    return MDBX_EINVAL;
+
+  const unsigned valid_turn_mask =
+      1 << MDBX_NEXT | 1 << MDBX_NEXT_DUP | 1 << MDBX_NEXT_NODUP |
+      1 << MDBX_PREV | 1 << MDBX_PREV_DUP | 1 << MDBX_PREV_NODUP |
+      1 << MDBX_NEXT_MULTIPLE | 1 << MDBX_PREV_MULTIPLE;
+  if (unlikely(turn_op > 30 || ((1 << turn_op) & valid_turn_mask) == 0))
+    return MDBX_EINVAL;
+
+  int rc = mdbx_cursor_get(mc, key, value, from_op);
+  if (unlikely(MDBX_IS_ERROR(rc)))
+    return rc;
+
+  cASSERT(mc, key != nullptr);
+  MDBX_val stub;
+  if (!value) {
+    value = &stub;
+    rc = cursor_get(mc, key, value, MDBX_GET_CURRENT);
+    if (unlikely(rc != MDBX_SUCCESS))
+      return rc;
+  }
+  for (;;) {
+    rc = predicate(context, key, value, arg);
+    if (rc != MDBX_RESULT_FALSE)
+      return rc;
+    rc = cursor_get(mc, key, value, turn_op);
+    if (rc != MDBX_SUCCESS)
+      return (rc == MDBX_NOTFOUND) ? MDBX_RESULT_FALSE : rc;
+  }
+}
+
 static int cursor_first_batch(MDBX_cursor *mc) {
   if (!(mc->mc_flags & C_INITIALIZED) || mc->mc_top) {
     int err = page_search(mc, NULL, MDBX_PS_FIRST);