Improve mysys/hash by caching hash_nr

This is done without using any additional memory
Added internal test case

This is similar to MDEV-7716

.gitignore

@@ -82,6 +82,7 @@ mysql-test/mysql-test-run
 mysql-test/var
 mysql-test-gcov.err
 mysql-test-gcov.msg
+mysys/test_hash
 mysys/thr_lock
 mysys/thr_timer
 packaging/rpm-oel/mysql.spec

include/hash.h

@@ -42,7 +42,7 @@ extern "C" {
 #define HASH_UNIQUE     1       /* hash_insert fails on duplicate key */
 #define HASH_THREAD_SPECIFIC 2  /* Mark allocated memory THREAD_SPECIFIC */
 
-typedef uint my_hash_value_type;
+typedef uint32 my_hash_value_type;
 typedef uchar *(*my_hash_get_key)(const uchar *,size_t*,my_bool);
 typedef my_hash_value_type (*my_hash_function)(CHARSET_INFO *,
                                                const uchar *, size_t);

mysys/CMakeLists.txt

@@ -96,6 +96,10 @@ ADD_EXECUTABLE(thr_timer thr_timer.c)
 TARGET_LINK_LIBRARIES(thr_timer mysys)
 SET_TARGET_PROPERTIES(thr_timer PROPERTIES COMPILE_FLAGS "-DMAIN")
 
+ADD_EXECUTABLE(test_hash hash.c)
+TARGET_LINK_LIBRARIES(test_hash mysys)
+SET_TARGET_PROPERTIES(test_hash PROPERTIES COMPILE_FLAGS "-DMAIN")
+
 IF(MSVC)
    INSTALL_DEBUG_TARGET(mysys DESTINATION ${INSTALL_LIBDIR}/debug)
 ENDIF()