I compute the max memory size that mysql will use

I compute the max memory size that mysql will use :

SHOW VARIABLES LIKE 'innodb_buffer_pool_size';
-- 12G
SHOW VARIABLES LIKE 'innodb_additional_mem_pool_size';
-- 16M
SHOW VARIABLES LIKE 'innodb_log_buffer_size';
-- 16M
SHOW VARIABLES LIKE 'thread_stack';
-- 192K
SHOW VARIABLES LIKE 'max_connections';
-- 200
show variables like 'tmp_table_size';
-- 100663296 , 96M

SET @kilo_bytes = 1024;
SET @mega_bytes = @kilo_bytes * 1024;
SET @giga_bytes = @mega_bytes * 1024;
SET @innodb_buffer_pool_size = 12 * @giga_bytes;
SET @innodb_additional_mem_pool_size = 16 * @mega_bytes;
SET @innodb_log_buffer_size = 16 * @mega_bytes;
SET @thread_stack = 192 * @kilo_bytes;

SELECT
( @@key_buffer_size + @@query_cache_size + @@tmp_table_size
+ @innodb_buffer_pool_size + @innodb_additional_mem_pool_size
+ @innodb_log_buffer_size
+ @@max_connections * (
@@read_buffer_size + @@read_rnd_buffer_size + @@sort_buffer_size
+ @@join_buffer_size + @@binlog_cache_size + @thread_stack
) ) / @giga_bytes AS MAX_MEMORY_GB;