diff --git a/mdbx.h b/mdbx.h
index c3c80831..5dc5db90 100644
--- a/mdbx.h
+++ b/mdbx.h
@@ -137,6 +137,100 @@ typedef pthread_t mdbx_tid_t;
 #define __has_attribute(x) (0)
 #endif /* __has_attribute */
 
+#ifndef __has_cpp_attribute
+#define __has_cpp_attribute(x) 0
+#endif /* __has_cpp_attribute */
+
+#ifndef __has_feature
+#define __has_feature(x) (0)
+#endif /* __has_feature */
+
+#ifndef __has_extension
+#define __has_extension(x) (0)
+#endif /* __has_extension */
+
+#ifndef __has_builtin
+#define __has_builtin(x) (0)
+#endif /* __has_builtin */
+
+#ifndef __pure_function
+/** Many functions have no effects except the return value and their
+ * return value depends only on the parameters and/or global variables.
+ * Such a function can be subject to common subexpression elimination
+ * and loop optimization just as an arithmetic operator would be.
+ * These functions should be declared with the attribute pure. */
+#if (defined(__GNUC__) || __has_attribute(__pure__)) &&                        \
+    (!defined(__clang__) /* https://bugs.llvm.org/show_bug.cgi?id=43275 */     \
+     || !defined(__cplusplus) || !__has_feature(cxx_exceptions))
+#define __pure_function __attribute__((__pure__))
+#elif defined(__cplusplus) && __has_cpp_attribute(gnu::pure) &&                \
+    (!defined(__clang__) || !__has_feature(cxx_exceptions))
+#define __pure_function [[gnu::pure]]
+#else
+#define __pure_function
+#endif
+#endif /* __pure_function */
+
+#ifndef __nothrow_pure_function
+/** Like \ref __pure_function with addition `noexcept` restriction
+ * that is compatible to CLANG and proposed [[pure]]. */
+#if defined(__GNUC__) ||                                                       \
+    (__has_attribute(__pure__) && __has_attribute(__nothrow__))
+#define __nothrow_pure_function __attribute__((__pure__, __nothrow__))
+#elif defined(__cplusplus) && __has_cpp_attribute(gnu::pure)
+#if __has_cpp_attribute(gnu::nothrow)
+#define __nothrow_pure_function [[gnu::pure, gnu::nothrow]]
+#else
+#define __nothrow_pure_function [[gnu::pure]]
+#endif
+#elif defined(__cplusplus) && __has_cpp_attribute(pure)
+#define __nothrow_pure_function [[pure]]
+#else
+#define __nothrow_pure_function
+#endif
+#endif /* __nothrow_pure_function */
+
+#ifndef __const_function
+/** Many functions do not examine any values except their arguments,
+ * and have no effects except the return value. Basically this is just
+ * slightly more strict class than the PURE attribute, since function
+ * is not allowed to read global memory.
+ *
+ * Note that a function that has pointer arguments and examines the
+ * data pointed to must not be declared const. Likewise, a function
+ * that calls a non-const function usually must not be const.
+ * It does not make sense for a const function to return void. */
+#if (defined(__GNUC__) || __has_attribute(__pure__)) &&                        \
+    (!defined(__clang__) /* https://bugs.llvm.org/show_bug.cgi?id=43275 */     \
+     || !defined(__cplusplus) || !__has_feature(cxx_exceptions))
+#define __const_function __attribute__((__const__))
+#elif defined(__cplusplus) && __has_cpp_attribute(gnu::const) &&               \
+    (!defined(__clang__) || !__has_feature(cxx_exceptions))
+#define __const_function [[gnu::const]]
+#else
+#define __const_function __pure_function
+#endif
+#endif /* __const_function */
+
+#ifndef __nothrow_const_function
+/** Like \ref __const_function with addition `noexcept` restriction
+ * that is compatible to CLANG and future [[const]]. */
+#if defined(__GNUC__) ||                                                       \
+    (__has_attribute(__const__) && __has_attribute(__nothrow__))
+#define __nothrow_const_function __attribute__((__const__, __nothrow__))
+#elif defined(__cplusplus) && __has_cpp_attribute(gnu::const)
+#if __has_cpp_attribute(gnu::nothrow)
+#define __nothrow_pure_function [[gnu::const, gnu::nothrow]]
+#else
+#define __nothrow_pure_function [[gnu::const]]
+#endif
+#elif defined(__cplusplus) && __has_cpp_attribute(const)
+#define __nothrow_const_function [[const]]
+#else
+#define __nothrow_const_function __nothrow_pure_function
+#endif
+#endif /* __nothrow_pure_function */
+
 #ifndef MDBX_DEPRECATED
 #ifdef __deprecated
 #define MDBX_DEPRECATED __deprecated
@@ -2138,40 +2232,47 @@ LIBMDBX_API int mdbx_is_readahead_reasonable(size_t volume,
 
 /** Returns the minimal database page size in bytes.
  * \ingroup c_statinfo */
-__inline intptr_t mdbx_limits_pgsize_min(void) { return MDBX_MIN_PAGESIZE; }
+__nothrow_const_function __inline intptr_t mdbx_limits_pgsize_min(void) {
+  return MDBX_MIN_PAGESIZE;
+}
 
 /** Returns the maximal database page size in bytes.
  * \ingroup c_statinfo */
-__inline intptr_t mdbx_limits_pgsize_max(void) { return MDBX_MAX_PAGESIZE; }
+__nothrow_const_function __inline intptr_t mdbx_limits_pgsize_max(void) {
+  return MDBX_MAX_PAGESIZE;
+}
 
 /** Returns minimal database size in bytes for given page size,
  * or -1 if pagesize is invalid.
  * \ingroup c_statinfo */
-LIBMDBX_API intptr_t mdbx_limits_dbsize_min(intptr_t pagesize);
+__nothrow_const_function LIBMDBX_API intptr_t
+mdbx_limits_dbsize_min(intptr_t pagesize);
 
 /** Returns maximal database size in bytes for given page size,
  * or -1 if pagesize is invalid.
  * \ingroup c_statinfo */
-LIBMDBX_API intptr_t mdbx_limits_dbsize_max(intptr_t pagesize);
+__nothrow_const_function LIBMDBX_API intptr_t
+mdbx_limits_dbsize_max(intptr_t pagesize);
 
 /** Returns maximal key size in bytes for given page size
  * and database flags, or -1 if pagesize is invalid.
  * \ingroup c_statinfo
  * \see db_flags */
-LIBMDBX_API intptr_t mdbx_limits_keysize_max(intptr_t pagesize,
-                                             MDBX_db_flags_t flags);
+__nothrow_const_function LIBMDBX_API intptr_t
+mdbx_limits_keysize_max(intptr_t pagesize, MDBX_db_flags_t flags);
 
 /** Returns maximal data size in bytes for given page size
  * and database flags, or -1 if pagesize is invalid.
  * \ingroup c_statinfo
  * \see db_flags */
-LIBMDBX_API intptr_t mdbx_limits_valsize_max(intptr_t pagesize,
-                                             MDBX_db_flags_t flags);
+__nothrow_const_function LIBMDBX_API intptr_t
+mdbx_limits_valsize_max(intptr_t pagesize, MDBX_db_flags_t flags);
 
 /** Returns maximal write transaction size (i.e. limit for summary volume of
  * dirty pages) in bytes for given page size, or -1 if pagesize is invalid.
  * \ingroup c_statinfo */
-LIBMDBX_API intptr_t mdbx_limits_txnsize_max(intptr_t pagesize);
+__nothrow_const_function LIBMDBX_API intptr_t
+mdbx_limits_txnsize_max(intptr_t pagesize);
 
 /** Set the maximum number of threads/reader slots for the environment.
  * \ingroup c_settings
@@ -2253,8 +2354,8 @@ LIBMDBX_API int mdbx_env_get_maxdbs(MDBX_env *env, MDBX_dbi *dbs);
  *
  * \returns The maximum size of a key can write,
  *          or -1 if something is wrong. */
-LIBMDBX_API int mdbx_env_get_maxkeysize_ex(const MDBX_env *env,
-                                           MDBX_db_flags_t flags);
+__nothrow_pure_function LIBMDBX_API int
+mdbx_env_get_maxkeysize_ex(const MDBX_env *env, MDBX_db_flags_t flags);
 
 /** Get the maximum size of data we can write.
  * \ingroup c_statinfo
@@ -2265,13 +2366,14 @@ LIBMDBX_API int mdbx_env_get_maxkeysize_ex(const MDBX_env *env,
  *
  * \returns The maximum size of a data can write,
  *          or -1 if something is wrong. */
-LIBMDBX_API int mdbx_env_get_maxvalsize_ex(const MDBX_env *env,
-                                           MDBX_db_flags_t flags);
+__nothrow_pure_function LIBMDBX_API int
+mdbx_env_get_maxvalsize_ex(const MDBX_env *env, MDBX_db_flags_t flags);
 
 /** \deprecated Please use \ref mdbx_env_get_maxkeysize_ex()
  *              and/or \ref mdbx_env_get_maxvalsize_ex()
  * \ingroup c_statinfo */
-MDBX_DEPRECATED LIBMDBX_API int mdbx_env_get_maxkeysize(const MDBX_env *env);
+__nothrow_pure_function MDBX_DEPRECATED LIBMDBX_API int
+mdbx_env_get_maxkeysize(const MDBX_env *env);
 
 /** Set application information associated with the \ref MDBX_env.
  * \ingroup c_settings
@@ -2289,7 +2391,8 @@ LIBMDBX_API int mdbx_env_set_userctx(MDBX_env *env, void *ctx);
  *
  * \param [in] env An environment handle returned by \ref mdbx_env_create()
  * \returns The pointer set by \ref mdbx_env_set_userctx(). */
-LIBMDBX_API void *mdbx_env_get_userctx(const MDBX_env *env);
+__nothrow_pure_function LIBMDBX_API void *
+mdbx_env_get_userctx(const MDBX_env *env);
 
 /** Create a transaction for use with the environment.
  * \ingroup c_transactions
@@ -2414,7 +2517,7 @@ LIBMDBX_API int mdbx_txn_info(const MDBX_txn *txn, MDBX_txn_info *info,
  * \ingroup c_transactions
  *
  * \param [in] txn  A transaction handle returned by \ref mdbx_txn_begin() */
-LIBMDBX_API MDBX_env *mdbx_txn_env(const MDBX_txn *txn);
+__nothrow_pure_function LIBMDBX_API MDBX_env *mdbx_txn_env(const MDBX_txn *txn);
 
 /** Return the transaction's flags.
  * \ingroup c_transactions
@@ -2425,7 +2528,7 @@ LIBMDBX_API MDBX_env *mdbx_txn_env(const MDBX_txn *txn);
  *
  * \returns A transaction flags, valid if input is an valid transaction,
  *          otherwise -1. */
-LIBMDBX_API int mdbx_txn_flags(const MDBX_txn *txn);
+__nothrow_pure_function LIBMDBX_API int mdbx_txn_flags(const MDBX_txn *txn);
 
 /** Return the transaction's ID.
  * \ingroup c_statinfo
@@ -2438,7 +2541,7 @@ LIBMDBX_API int mdbx_txn_flags(const MDBX_txn *txn);
  *
  * \returns A transaction ID, valid if input is an active transaction,
  *          otherwise 0. */
-LIBMDBX_API uint64_t mdbx_txn_id(const MDBX_txn *txn);
+__nothrow_pure_function LIBMDBX_API uint64_t mdbx_txn_id(const MDBX_txn *txn);
 
 /** Commit all the operations of a transaction into the database.
  * \ingroup c_transactions
@@ -2748,15 +2851,28 @@ mdbx_dbi_open_ex(MDBX_txn *txn, const char *name, MDBX_db_flags_t flags,
  * and IEEE754 double values in one index for JSON-numbers with restriction for
  * integer numbers range corresponding to RFC-7159, i.e. \f$[-2^{53}+1,
  * 2^{53}-1]\f$. See bottom of page 6 at https://tools.ietf.org/html/rfc7159 */
-LIBMDBX_API uint64_t mdbx_key_from_jsonInteger(const int64_t json_integer);
-LIBMDBX_API uint64_t mdbx_key_from_double(const double ieee754_64bit);
-LIBMDBX_API uint64_t mdbx_key_from_ptrdouble(const double *const ieee754_64bit);
-LIBMDBX_API uint32_t mdbx_key_from_float(const float ieee754_32bit);
-LIBMDBX_API uint32_t mdbx_key_from_ptrfloat(const float *const ieee754_32bit);
-__inline uint64_t mdbx_key_from_int64(const int64_t i64) {
+__nothrow_const_function LIBMDBX_API uint64_t
+mdbx_key_from_jsonInteger(const int64_t json_integer);
+
+__nothrow_const_function LIBMDBX_API uint64_t
+mdbx_key_from_double(const double ieee754_64bit);
+
+__nothrow_pure_function LIBMDBX_API uint64_t
+mdbx_key_from_ptrdouble(const double *const ieee754_64bit);
+
+__nothrow_const_function LIBMDBX_API uint32_t
+mdbx_key_from_float(const float ieee754_32bit);
+
+__nothrow_const_function LIBMDBX_API uint32_t
+mdbx_key_from_ptrfloat(const float *const ieee754_32bit);
+
+__nothrow_const_function __inline uint64_t
+mdbx_key_from_int64(const int64_t i64) {
   return UINT64_C(0x8000000000000000) + i64;
 }
-__inline uint32_t mdbx_key_from_int32(const int32_t i32) {
+
+__nothrow_const_function __inline uint32_t
+mdbx_key_from_int32(const int32_t i32) {
   return UINT32_C(0x80000000) + i32;
 }
 /** @} */
@@ -2764,11 +2880,16 @@ __inline uint32_t mdbx_key_from_int32(const int32_t i32) {
 /** \defgroup key2value Key-to-Value functions to avoid custom comparators
  * \see value2key
  * @{ */
-LIBMDBX_API int64_t mdbx_jsonInteger_from_key(const MDBX_val);
-LIBMDBX_API double mdbx_double_from_key(const MDBX_val);
-LIBMDBX_API float mdbx_float_from_key(const MDBX_val);
-LIBMDBX_API int32_t mdbx_int32_from_key(const MDBX_val);
-LIBMDBX_API int64_t mdbx_int64_from_key(const MDBX_val);
+__nothrow_pure_function LIBMDBX_API int64_t
+mdbx_jsonInteger_from_key(const MDBX_val);
+
+__nothrow_pure_function LIBMDBX_API double mdbx_double_from_key(const MDBX_val);
+
+__nothrow_pure_function LIBMDBX_API float mdbx_float_from_key(const MDBX_val);
+
+__nothrow_pure_function LIBMDBX_API int32_t mdbx_int32_from_key(const MDBX_val);
+
+__nothrow_pure_function LIBMDBX_API int64_t mdbx_int64_from_key(const MDBX_val);
 /** @} */
 
 /** Retrieve statistics for a database.
@@ -3181,7 +3302,8 @@ LIBMDBX_API int mdbx_cursor_renew(MDBX_txn *txn, MDBX_cursor *cursor);
  * \ingroup c_cursors
  *
  * \param [in] cursor A cursor handle returned by \ref mdbx_cursor_open(). */
-LIBMDBX_API MDBX_txn *mdbx_cursor_txn(const MDBX_cursor *cursor);
+__nothrow_pure_function LIBMDBX_API MDBX_txn *
+mdbx_cursor_txn(const MDBX_cursor *cursor);
 
 /** Return the cursor's database handle.
  * \ingroup c_cursors
@@ -3347,7 +3469,8 @@ LIBMDBX_API int mdbx_cursor_count(const MDBX_cursor *cursor, size_t *pcount);
  *                             positioned
  * \retval MDBX_RESULT_FALSE   A data is available
  * \retval Otherwise the error code */
-LIBMDBX_API int mdbx_cursor_eof(const MDBX_cursor *cursor);
+__nothrow_pure_function LIBMDBX_API int
+mdbx_cursor_eof(const MDBX_cursor *cursor);
 
 /** Determines whether the cursor is pointed to the first key-value pair or
  * not.
@@ -3358,9 +3481,10 @@ LIBMDBX_API int mdbx_cursor_eof(const MDBX_cursor *cursor);
  * \returns A MDBX_RESULT_TRUE or MDBX_RESULT_FALSE value,
  *          otherwise the error code:
  * \retval MDBX_RESULT_TRUE   Cursor positioned to the first key-value pair
- * \retval MDBX_RESULT_FALSE  Cursor NOT positioned to the first key-value pair
- * \retval Otherwise the error code */
-LIBMDBX_API int mdbx_cursor_on_first(const MDBX_cursor *cursor);
+ * \retval MDBX_RESULT_FALSE  Cursor NOT positioned to the first key-value
+ * pair \retval Otherwise the error code */
+__nothrow_pure_function LIBMDBX_API int
+mdbx_cursor_on_first(const MDBX_cursor *cursor);
 
 /** Determines whether the cursor is pointed to the last key-value pair or not.
  * \ingroup c_cursors
@@ -3372,7 +3496,8 @@ LIBMDBX_API int mdbx_cursor_on_first(const MDBX_cursor *cursor);
  * \retval MDBX_RESULT_TRUE   Cursor positioned to the last key-value pair
  * \retval MDBX_RESULT_FALSE  Cursor NOT positioned to the last key-value pair
  * \retval Otherwise the error code */
-LIBMDBX_API int mdbx_cursor_on_last(const MDBX_cursor *cursor);
+__nothrow_pure_function LIBMDBX_API int
+mdbx_cursor_on_last(const MDBX_cursor *cursor);
 
 /** \addtogroup c_rqest
  * \details \note The estimation result varies greatly depending on the filling
@@ -3512,7 +3637,8 @@ LIBMDBX_API int mdbx_estimate_range(MDBX_txn *txn, MDBX_dbi dbi,
  * \retval MDBX_RESULT_TRUE    Given address is on the dirty page.
  * \retval MDBX_RESULT_FALSE   Given address is NOT on the dirty page.
  * \retval Otherwise the error code. */
-LIBMDBX_API int mdbx_is_dirty(const MDBX_txn *txn, const void *ptr);
+__nothrow_pure_function LIBMDBX_API int mdbx_is_dirty(const MDBX_txn *txn,
+                                                      const void *ptr);
 
 /** Sequence generation for a database.
  * \ingroup c_crud
@@ -3552,12 +3678,15 @@ LIBMDBX_API int mdbx_dbi_sequence(MDBX_txn *txn, MDBX_dbi dbi, uint64_t *result,
  * \param [in] b     The second item to compare.
  *
  * \returns < 0 if a < b, 0 if a == b, > 0 if a > b */
-LIBMDBX_API int mdbx_cmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
-                         const MDBX_val *b);
+__nothrow_pure_function LIBMDBX_API int mdbx_cmp(const MDBX_txn *txn,
+                                                 MDBX_dbi dbi,
+                                                 const MDBX_val *a,
+                                                 const MDBX_val *b);
 
 /** Returns default internal key's comparator for given database flags.
  * \ingroup c_extra */
-LIBMDBX_API MDBX_cmp_func *mdbx_get_keycmp(MDBX_db_flags_t flags);
+__nothrow_const_function LIBMDBX_API MDBX_cmp_func *
+mdbx_get_keycmp(MDBX_db_flags_t flags);
 
 /** Compare two data items according to a particular database.
  * \ingroup c_crud
@@ -3573,12 +3702,15 @@ LIBMDBX_API MDBX_cmp_func *mdbx_get_keycmp(MDBX_db_flags_t flags);
  * \param [in] b     The second item to compare.
  *
  * \returns < 0 if a < b, 0 if a == b, > 0 if a > b */
-LIBMDBX_API int mdbx_dcmp(const MDBX_txn *txn, MDBX_dbi dbi, const MDBX_val *a,
-                          const MDBX_val *b);
+__nothrow_pure_function LIBMDBX_API int mdbx_dcmp(const MDBX_txn *txn,
+                                                  MDBX_dbi dbi,
+                                                  const MDBX_val *a,
+                                                  const MDBX_val *b);
 
 /** Returns default internal data's comparator for given database flags
  * \ingroup c_extra */
-LIBMDBX_API MDBX_cmp_func *mdbx_get_datacmp(MDBX_db_flags_t flags);
+__nothrow_const_function LIBMDBX_API MDBX_cmp_func *
+mdbx_get_datacmp(MDBX_db_flags_t flags);
 
 /** A callback function used to enumerate the reader lock table.
  * \ingroup c_statinfo
@@ -3764,7 +3896,8 @@ LIBMDBX_API int mdbx_env_set_oomfunc(MDBX_env *env, MDBX_oom_func *oom_func);
  * \param [in] env   An environment handle returned by \ref mdbx_env_create().
  *
  * \returns A MDBX_oom_func function or NULL if disabled. */
-LIBMDBX_API MDBX_oom_func *mdbx_env_get_oomfunc(const MDBX_env *env);
+__nothrow_pure_function LIBMDBX_API MDBX_oom_func *
+mdbx_env_get_oomfunc(const MDBX_env *env);
 
 /** \defgroup btree_traversal B-tree Traversal
  * This is internal API for mdbx_chk tool. You should avoid to use it, except
diff --git a/src/core.c b/src/core.c
index 5d1d5ca6..1646cf19 100644
--- a/src/core.c
+++ b/src/core.c
@@ -40,7 +40,7 @@
 /*------------------------------------------------------------------------------
  * Internal inlines */
 
-static __pure_function unsigned log2n(size_t value) {
+__nothrow_const_function static unsigned log2n(size_t value) {
   assert(value > 0 && value < INT32_MAX && is_powerof2(value));
   assert((value & -(int32_t)value) == value);
 #if __GNUC_PREREQ(4, 1) || __has_builtin(__builtin_ctzl)
@@ -60,14 +60,14 @@ static __pure_function unsigned log2n(size_t value) {
 /*------------------------------------------------------------------------------
  * Unaligned access */
 
-static __pure_function __maybe_unused __always_inline unsigned
+__nothrow_const_function static __maybe_unused __always_inline unsigned
 field_alignment(unsigned alignment_baseline, size_t field_offset) {
   unsigned merge = alignment_baseline | (unsigned)field_offset;
   return merge & -(int)merge;
 }
 
 /* read-thunk for UB-sanitizer */
-static __pure_function __always_inline uint8_t
+__nothrow_pure_function static __always_inline uint8_t
 peek_u8(const uint8_t *const __restrict ptr) {
   return *ptr;
 }
@@ -78,7 +78,7 @@ static __always_inline void poke_u8(uint8_t *const __restrict ptr,
   *ptr = v;
 }
 
-static __pure_function __always_inline uint16_t
+__nothrow_pure_function static __always_inline uint16_t
 unaligned_peek_u16(const unsigned expected_alignment, const void *const ptr) {
   assert((uintptr_t)ptr % expected_alignment == 0);
   if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(uint16_t)) == 0)
@@ -100,7 +100,7 @@ unaligned_poke_u16(const unsigned expected_alignment,
     memcpy(ptr, &v, sizeof(v));
 }
 
-static __pure_function __always_inline uint32_t unaligned_peek_u32(
+__nothrow_pure_function static __always_inline uint32_t unaligned_peek_u32(
     const unsigned expected_alignment, const void *const __restrict ptr) {
   assert((uintptr_t)ptr % expected_alignment == 0);
   if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(uint32_t)) == 0)
@@ -132,7 +132,7 @@ unaligned_poke_u32(const unsigned expected_alignment,
     memcpy(ptr, &v, sizeof(v));
 }
 
-static __pure_function __always_inline uint64_t unaligned_peek_u64(
+__nothrow_pure_function static __always_inline uint64_t unaligned_peek_u64(
     const unsigned expected_alignment, const void *const __restrict ptr) {
   assert((uintptr_t)ptr % expected_alignment == 0);
   if (MDBX_UNALIGNED_OK || (expected_alignment % sizeof(uint64_t)) == 0)
@@ -185,7 +185,7 @@ unaligned_poke_u64(const unsigned expected_alignment,
   unaligned_poke_u64(1, (char *)(ptr) + offsetof(struct, field), value)
 
 /* Get the page number pointed to by a branch node */
-static __pure_function __always_inline pgno_t
+__nothrow_pure_function static __always_inline pgno_t
 node_pgno(const MDBX_node *const __restrict node) {
   pgno_t pgno = UNALIGNED_PEEK_32(node, MDBX_node, mn_pgno32);
   if (sizeof(pgno) > 4)
@@ -205,7 +205,7 @@ static __always_inline void node_set_pgno(MDBX_node *const __restrict node,
 }
 
 /* Get the size of the data in a leaf node */
-static __pure_function __always_inline size_t
+__nothrow_pure_function static __always_inline size_t
 node_ds(const MDBX_node *const __restrict node) {
   return UNALIGNED_PEEK_32(node, MDBX_node, mn_dsize);
 }
@@ -218,7 +218,7 @@ static __always_inline void node_set_ds(MDBX_node *const __restrict node,
 }
 
 /* The size of a key in a node */
-static __pure_function __always_inline size_t
+__nothrow_pure_function static __always_inline size_t
 node_ks(const MDBX_node *const __restrict node) {
   return UNALIGNED_PEEK_16(node, MDBX_node, mn_ksize);
 }
@@ -230,7 +230,7 @@ static __always_inline void node_set_ks(MDBX_node *const __restrict node,
   UNALIGNED_POKE_16(node, MDBX_node, mn_ksize, (uint16_t)size);
 }
 
-static __pure_function __always_inline uint8_t
+__nothrow_pure_function static __always_inline uint8_t
 node_flags(const MDBX_node *const __restrict node) {
   return UNALIGNED_PEEK_8(node, MDBX_node, mn_flags);
 }
@@ -244,29 +244,29 @@ static __always_inline void node_set_flags(MDBX_node *const __restrict node,
 #define NODESIZE offsetof(MDBX_node, mn_data)
 
 /* Address of the key for the node */
-static __pure_function __always_inline void *
+__nothrow_pure_function static __always_inline void *
 node_key(const MDBX_node *const __restrict node) {
   return (char *)node + NODESIZE;
 }
 
 /* Address of the data for a node */
-static __pure_function __always_inline void *
+__nothrow_pure_function static __always_inline void *
 node_data(const MDBX_node *const __restrict node) {
   return (char *)node_key(node) + node_ks(node);
 }
 
 /* Size of a node in a leaf page with a given key and data.
  * This is node header plus key plus data size. */
-static __pure_function __always_inline size_t
+__nothrow_const_function static __always_inline size_t
 node_size_len(const size_t key_len, const size_t value_len) {
   return NODESIZE + EVEN(key_len + value_len);
 }
-static __pure_function __always_inline size_t node_size(const MDBX_val *key,
-                                                        const MDBX_val *value) {
+__nothrow_pure_function static __always_inline size_t
+node_size(const MDBX_val *key, const MDBX_val *value) {
   return node_size_len(key ? key->iov_len : 0, value ? value->iov_len : 0);
 }
 
-static __pure_function __always_inline pgno_t
+__nothrow_pure_function static __always_inline pgno_t
 peek_pgno(const void *const __restrict ptr) {
   if (sizeof(pgno_t) == sizeof(uint32_t))
     return (pgno_t)unaligned_peek_u32(1, ptr);
@@ -289,7 +289,7 @@ static __always_inline void poke_pgno(void *const __restrict ptr,
     memcpy(ptr, &pgno, sizeof(pgno));
 }
 
-static __pure_function __always_inline pgno_t
+__nothrow_pure_function static __always_inline pgno_t
 node_largedata_pgno(const MDBX_node *const __restrict node) {
   assert(node_flags(node) & F_BIGDATA);
   return peek_pgno(node_data(node));
@@ -411,9 +411,8 @@ __cold intptr_t mdbx_limits_valsize_max(intptr_t pagesize,
  * size will only include the key and not the data. Sizes are always
  * rounded up to an even number of bytes, to guarantee 2-byte alignment
  * of the MDBX_node headers. */
-static __pure_function __always_inline size_t leaf_size(const MDBX_env *env,
-                                                        const MDBX_val *key,
-                                                        const MDBX_val *data) {
+__nothrow_pure_function static __always_inline size_t
+leaf_size(const MDBX_env *env, const MDBX_val *key, const MDBX_val *data) {
   size_t node_bytes = node_size(key, data);
   /* NOTE: The actual limit is LEAF_NODEMAX(env->me_psize), but it reasonable to
    * use env->me_branch_nodemax (which is 3 times less) as the treshold because:
@@ -455,8 +454,8 @@ static __pure_function __always_inline size_t leaf_size(const MDBX_env *env,
  * [in] key The key for the node.
  *
  * Returns The number of bytes needed to store the node. */
-static __pure_function __always_inline size_t branch_size(const MDBX_env *env,
-                                                          const MDBX_val *key) {
+__nothrow_pure_function static __always_inline size_t
+branch_size(const MDBX_env *env, const MDBX_val *key) {
   /* Size of a node in a branch page with a given key.
    * This is just the node header plus the key, there is no data. */
   size_t node_bytes = node_size(key, nullptr);
@@ -471,7 +470,7 @@ static __pure_function __always_inline size_t branch_size(const MDBX_env *env,
   return node_bytes + sizeof(indx_t);
 }
 
-static __pure_function __always_inline uint16_t
+__nothrow_const_function static __always_inline uint16_t
 flags_db2sub(uint16_t db_flags) {
   uint16_t sub_flags = db_flags & MDBX_DUPFIXED;
 
@@ -492,81 +491,84 @@ flags_db2sub(uint16_t db_flags) {
 
 /*----------------------------------------------------------------------------*/
 
-static __pure_function __always_inline size_t pgno2bytes(const MDBX_env *env,
-                                                         pgno_t pgno) {
+__nothrow_pure_function static __always_inline size_t
+pgno2bytes(const MDBX_env *env, pgno_t pgno) {
   mdbx_assert(env, (1u << env->me_psize2log) == env->me_psize);
   return ((size_t)pgno) << env->me_psize2log;
 }
 
-static __pure_function __always_inline MDBX_page *pgno2page(const MDBX_env *env,
-                                                            pgno_t pgno) {
+__nothrow_pure_function static __always_inline MDBX_page *
+pgno2page(const MDBX_env *env, pgno_t pgno) {
   return (MDBX_page *)(env->me_map + pgno2bytes(env, pgno));
 }
 
-static __pure_function __always_inline pgno_t bytes2pgno(const MDBX_env *env,
-                                                         size_t bytes) {
+__nothrow_pure_function static __always_inline pgno_t
+bytes2pgno(const MDBX_env *env, size_t bytes) {
   mdbx_assert(env, (env->me_psize >> env->me_psize2log) == 1);
   return (pgno_t)(bytes >> env->me_psize2log);
 }
 
-static __pure_function size_t pgno_align2os_bytes(const MDBX_env *env,
-                                                  pgno_t pgno) {
+__nothrow_pure_function static size_t pgno_align2os_bytes(const MDBX_env *env,
+                                                          pgno_t pgno) {
   return ceil_powerof2(pgno2bytes(env, pgno), env->me_os_psize);
 }
 
-static __pure_function pgno_t pgno_align2os_pgno(const MDBX_env *env,
-                                                 pgno_t pgno) {
+__nothrow_pure_function static pgno_t pgno_align2os_pgno(const MDBX_env *env,
+                                                         pgno_t pgno) {
   return bytes2pgno(env, pgno_align2os_bytes(env, pgno));
 }
 
-static __pure_function size_t bytes_align2os_bytes(const MDBX_env *env,
-                                                   size_t bytes) {
+__nothrow_pure_function static size_t bytes_align2os_bytes(const MDBX_env *env,
+                                                           size_t bytes) {
   return ceil_powerof2(ceil_powerof2(bytes, env->me_psize), env->me_os_psize);
 }
 
 /* Address of first usable data byte in a page, after the header */
-static __pure_function __always_inline void *page_data(const MDBX_page *mp) {
+__nothrow_pure_function static __always_inline void *
+page_data(const MDBX_page *mp) {
   return (char *)mp + PAGEHDRSZ;
 }
 
-static __pure_function __always_inline const MDBX_page *
+__nothrow_pure_function static __always_inline const MDBX_page *
 data_page(const void *data) {
   return container_of(data, MDBX_page, mp_ptrs);
 }
 
-static __pure_function __always_inline MDBX_meta *page_meta(MDBX_page *mp) {
+__nothrow_pure_function static __always_inline MDBX_meta *
+page_meta(MDBX_page *mp) {
   return (MDBX_meta *)page_data(mp);
 }
 
 /* Number of nodes on a page */
-static __pure_function __always_inline unsigned
+__nothrow_pure_function static __always_inline unsigned
 page_numkeys(const MDBX_page *mp) {
   return mp->mp_lower >> 1;
 }
 
 /* The amount of space remaining in the page */
-static __pure_function __always_inline unsigned page_room(const MDBX_page *mp) {
+__nothrow_pure_function static __always_inline unsigned
+page_room(const MDBX_page *mp) {
   return mp->mp_upper - mp->mp_lower;
 }
 
-static __pure_function __always_inline unsigned
+__nothrow_pure_function static __always_inline unsigned
 page_space(const MDBX_env *env) {
   STATIC_ASSERT(PAGEHDRSZ % 2 == 0);
   return env->me_psize - PAGEHDRSZ;
 }
 
-static __pure_function __always_inline unsigned page_used(const MDBX_env *env,
-                                                          const MDBX_page *mp) {
+__nothrow_pure_function static __always_inline unsigned
+page_used(const MDBX_env *env, const MDBX_page *mp) {
   return page_space(env) - page_room(mp);
 }
 
 /* The percentage of space used in the page, in a percents. */
-static __pure_function __maybe_unused __inline double
+__nothrow_pure_function static __maybe_unused __inline double
 page_fill(const MDBX_env *env, const MDBX_page *mp) {
   return page_used(env, mp) * 100.0 / page_space(env);
 }
 
-static __pure_function __inline bool
+__nothrow_pure_function static __inline bool
 page_fill_enough(const MDBX_page *mp, unsigned spaceleft_threshold,
                  unsigned minkeys_threshold) {
   return page_room(mp) < spaceleft_threshold &&
@@ -574,14 +576,14 @@ page_fill_enough(const MDBX_page *mp, unsigned spaceleft_threshold,
 }
 
 /* The number of overflow pages needed to store the given size. */
-static __pure_function __always_inline pgno_t
+__nothrow_pure_function static __always_inline pgno_t
 number_of_ovpages(const MDBX_env *env, size_t bytes) {
   return bytes2pgno(env, PAGEHDRSZ - 1 + bytes) + 1;
 }
 
 /* Address of node i in page p */
-static __pure_function __always_inline MDBX_node *page_node(const MDBX_page *mp,
-                                                            unsigned i) {
+__nothrow_pure_function static __always_inline MDBX_node *
+page_node(const MDBX_page *mp, unsigned i) {
   assert((mp->mp_flags & (P_LEAF2 | P_OVERFLOW | P_META)) == 0);
   assert(page_numkeys(mp) > (unsigned)(i));
   assert(mp->mp_ptrs[i] % 2 == 0);
@@ -591,7 +593,7 @@ static __pure_function __always_inline MDBX_node *page_node(const MDBX_page *mp,
 /* The address of a key in a LEAF2 page.
  * LEAF2 pages are used for MDBX_DUPFIXED sorted-duplicate sub-DBs.
  * There are no node headers, keys are stored contiguously. */
-static __pure_function __always_inline void *
+__nothrow_pure_function static __always_inline void *
 page_leaf2key(const MDBX_page *mp, unsigned i, size_t keysize) {
   assert((mp->mp_flags & (P_BRANCH | P_LEAF | P_LEAF2 | P_OVERFLOW | P_META)) ==
          (P_LEAF | P_LEAF2));
@@ -1362,7 +1364,7 @@ static __inline void lcklist_unlock(void) {
 #endif
 }
 
-static uint64_t rrxmrrxmsx_0(uint64_t v) {
+__nothrow_const_function static uint64_t rrxmrrxmsx_0(uint64_t v) {
   /* Pelle Evensen's mixer, https://bit.ly/2HOfynt */
   v ^= (v << 39 | v >> 25) ^ (v << 14 | v >> 50);
   v *= UINT64_C(0xA24BAED4963EE407);
diff --git a/src/defs.h b/src/defs.h
index d062b7c1..90428add 100644
--- a/src/defs.h
+++ b/src/defs.h
@@ -43,22 +43,6 @@
 #   endif
 #endif /* __GLIBC_PREREQ */
 
-#ifndef __has_attribute
-#   define __has_attribute(x) (0)
-#endif
-
-#ifndef __has_feature
-#   define __has_feature(x) (0)
-#endif
-
-#ifndef __has_extension
-#   define __has_extension(x) (0)
-#endif
-
-#ifndef __has_builtin
-#   define __has_builtin(x) (0)
-#endif
-
 #ifndef __has_warning
 #   define __has_warning(x) (0)
 #endif
@@ -67,10 +51,6 @@
 #   define __has_include(x) (0)
 #endif
 
-#ifndef __has_cpp_attribute
-#   define __has_cpp_attribute(x) (0)
-#endif
-
 #if __has_feature(thread_sanitizer)
 #   define __SANITIZE_THREAD__ 1
 #endif
@@ -196,40 +176,6 @@
 #   endif
 #endif /* __nothrow */
 
-#ifndef __pure_function
-    /* Many functions have no effects except the return value and their
-     * return value depends only on the parameters and/or global variables.
-     * Such a function can be subject to common subexpression elimination
-     * and loop optimization just as an arithmetic operator would be.
-     * These functions should be declared with the attribute pure. */
-#   if (defined(__GNUC__) || __has_attribute(__pure__)) &&                     \
-        (!defined(__clang__) /* https://bugs.llvm.org/show_bug.cgi?id=43275 */ \
-         || !defined(__cplusplus) || !__has_feature(cxx_exceptions))
-#       define __pure_function __attribute__((__pure__))
-#   else
-#       define __pure_function
-#   endif
-#endif /* __pure_function */
-
-#ifndef __const_function
-    /* Many functions do not examine any values except their arguments,
-     * and have no effects except the return value. Basically this is just
-     * slightly more strict class than the PURE attribute, since function
-     * is not allowed to read global memory.
-     *
-     * Note that a function that has pointer arguments and examines the
-     * data pointed to must not be declared const. Likewise, a function
-     * that calls a non-const function usually must not be const.
-     * It does not make sense for a const function to return void. */
-#   if (defined(__GNUC__) || __has_attribute(__pure__)) &&                     \
-        (!defined(__clang__) /* https://bugs.llvm.org/show_bug.cgi?id=43275 */ \
-         || !defined(__cplusplus) || !__has_feature(cxx_exceptions))
-#       define __const_function __attribute__((__const__))
-#   else
-#       define __const_function
-#   endif
-#endif /* __const_function */
-
 #ifndef __hidden
 #   if defined(__GNUC__) || __has_attribute(__visibility__)
 #       define __hidden __attribute__((__visibility__("hidden")))
diff --git a/src/internals.h b/src/internals.h
index 07a84880..094f6571 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -1354,12 +1354,14 @@ typedef struct MDBX_node {
 /* Do not spill pages to disk if txn is getting full, may fail instead */
 #define MDBX_NOSPILL 0x8000
 
-static __maybe_unused __inline pgno_t pgno_add(pgno_t base, pgno_t augend) {
+__nothrow_const_function static __maybe_unused __inline pgno_t
+pgno_add(pgno_t base, pgno_t augend) {
   assert(base <= MAX_PAGENO);
   return (augend < MAX_PAGENO - base) ? base + augend : MAX_PAGENO;
 }
 
-static __maybe_unused __inline pgno_t pgno_sub(pgno_t base, pgno_t subtrahend) {
+__nothrow_const_function static __maybe_unused __inline pgno_t
+pgno_sub(pgno_t base, pgno_t subtrahend) {
   assert(base >= MIN_PAGENO);
   return (subtrahend < base - MIN_PAGENO) ? base - subtrahend : MIN_PAGENO;
 }
@@ -1373,18 +1375,18 @@ static __maybe_unused __inline void mdbx_jitter4testing(bool tiny) {
 #endif
 }
 
-static __pure_function __always_inline __maybe_unused bool
+__nothrow_const_function static __always_inline __maybe_unused bool
 is_powerof2(size_t x) {
   return (x & (x - 1)) == 0;
 }
 
-static __pure_function __always_inline __maybe_unused size_t
+__nothrow_const_function static __always_inline __maybe_unused size_t
 floor_powerof2(size_t value, size_t granularity) {
   assert(is_powerof2(granularity));
   return value & ~(granularity - 1);
 }
 
-static __pure_function __always_inline __maybe_unused size_t
+__nothrow_const_function static __always_inline __maybe_unused size_t
 ceil_powerof2(size_t value, size_t granularity) {
   return floor_powerof2(value + granularity - 1, granularity);
 }
diff --git a/src/osal.h b/src/osal.h
index 8fef7cf7..7e6fa999 100644
--- a/src/osal.h
+++ b/src/osal.h
@@ -511,7 +511,8 @@ MDBX_INTERNAL_VAR bool
 /* Get the size of a memory page for the system.
  * This is the basic size that the platform's memory manager uses, and is
  * fundamental to the use of memory-mapped files. */
-static __maybe_unused __inline size_t mdbx_syspagesize(void) {
+__nothrow_const_function static __maybe_unused __inline size_t
+mdbx_syspagesize(void) {
 #if defined(_WIN32) || defined(_WIN64)
   SYSTEM_INFO si;
   GetSystemInfo(&si);