Sequences with negative numbers and auto_increment_increment crashes

This also fixes MDEV-16313 Assertion `next_free_value % real_increment == offset' fails upon CREATE SEQUENCE in galera cluster

Fixed by adding llabs() to assert.
Also adjusted auto_increment_offset to mod auto_increment_increment.

mysql-test/suite/sql_sequence/auto_increment.result

+set global auto_increment_increment= 2, auto_increment_offset= 2;
+create sequence s start with -3 minvalue= -1000 increment 0;
+select nextval(s);
+nextval(s)
+-2
+select nextval(s);
+nextval(s)
+0
+flush tables;
+select nextval(s);
+nextval(s)
+1998
+drop sequence s;
+set global auto_increment_increment= 2, auto_increment_offset= 1;
+create sequence s start with -3 minvalue= -1000 increment 0;
+select nextval(s);
+nextval(s)
+-3
+select nextval(s);
+nextval(s)
+-1
+select nextval(s);
+nextval(s)
+1
+flush tables;
+select nextval(s);
+nextval(s)
+1997
+drop sequence s;
+set global auto_increment_increment= default, auto_increment_offset= default;

mysql-test/suite/sql_sequence/auto_increment.test

+--source include/have_sequence.inc
+
+#
+# tests with auto_increment_increment and auto_increment_offset
+#
+
+set global auto_increment_increment= 2, auto_increment_offset= 2;
+
+create sequence s start with -3 minvalue= -1000 increment 0;
+
+select nextval(s);
+select nextval(s);
+flush tables;
+select nextval(s);
+drop sequence s;
+
+set global auto_increment_increment= 2, auto_increment_offset= 1;
+
+create sequence s start with -3 minvalue= -1000 increment 0;
+
+select nextval(s);
+select nextval(s);
+select nextval(s);
+flush tables;
+select nextval(s);
+drop sequence s;
+
+# Clean up
+
+set global auto_increment_increment= default, auto_increment_offset= default;

mysql-test/suite/sql_sequence/next.result

@@ -519,3 +519,18 @@ create temporary table tmp (i int);
 select next value for tmp;
 ERROR 42S02: 'test.tmp' is not a SEQUENCE
 drop table tmp;
+#
+# Test negative numbers
+#
+create sequence s start with 1 minvalue=-1000 maxvalue=1000 increment -1;
+select next value for s;
+next value for s
+1
+select next value for s;
+next value for s
+0
+flush tables;
+select next value for s;
+next value for s
+-999
+drop sequence s;

mysql-test/suite/sql_sequence/next.test

@@ -269,3 +269,14 @@ create temporary table tmp (i int);
 --error ER_NOT_SEQUENCE
 select next value for tmp;
 drop table tmp;
+
+--echo #
+--echo # Test negative numbers
+--echo #
+
+create sequence s start with 1 minvalue=-1000 maxvalue=1000 increment -1;
+select next value for s;
+select next value for s;
+flush tables;
+select next value for s;
+drop sequence s;

sql/sql_sequence.cc

@@ -542,7 +542,8 @@ void sequence_definition::adjust_values(longlong next_value)
 
     if ((real_increment= global_system_variables.auto_increment_increment)
         != 1)
-      offset= global_system_variables.auto_increment_offset;
+      offset= (global_system_variables.auto_increment_offset %
+               global_system_variables.auto_increment_increment);
 
     /*
       Ensure that next_free_value has the right offset, so that we
@@ -564,7 +565,7 @@ void sequence_definition::adjust_values(longlong next_value)
     else
     {
       next_free_value+= to_add;
-      DBUG_ASSERT(next_free_value % real_increment == offset);
+      DBUG_ASSERT(llabs(next_free_value % real_increment) == offset);
     }
   }
 }