MDEV-8473: mysqlbinlog -v does not properly decode DECIMAL values in an RBR log

Backport of upstream patch. revno: 5696

mysql-test/suite/binlog/r/binlog_mysqlbinlog_row.result

@@ -1409,7 +1409,7 @@ BEGIN
 #010909  4:46:40 server id 1  end_log_pos # 	Write_rows: table id # flags: STMT_END_F
 ### INSERT INTO `test`.`t1`
 ### SET
-###   @1=000000124.450000000 /* DECIMAL(10,5) meta=2565 nullable=1 is_null=0 */
+###   @1=124.45000 /* DECIMAL(10,5) meta=2565 nullable=1 is_null=0 */
 # at #
 #010909  4:46:40 server id 1  end_log_pos # 	Query	thread_id=#	exec_time=#	error_code=0
 SET TIMESTAMP=1000000000/*!*/;
@@ -1426,7 +1426,7 @@ BEGIN
 #010909  4:46:40 server id 1  end_log_pos # 	Write_rows: table id # flags: STMT_END_F
 ### INSERT INTO `test`.`t1`
 ### SET
-###   @1=-000000543.210000000 /* DECIMAL(10,5) meta=2565 nullable=1 is_null=0 */
+###   @1=-543.21000 /* DECIMAL(10,5) meta=2565 nullable=1 is_null=0 */
 # at #
 #010909  4:46:40 server id 1  end_log_pos # 	Query	thread_id=#	exec_time=#	error_code=0
 SET TIMESTAMP=1000000000/*!*/;
@@ -1443,7 +1443,7 @@ BEGIN
 #010909  4:46:40 server id 1  end_log_pos # 	Delete_rows: table id # flags: STMT_END_F
 ### DELETE FROM `test`.`t1`
 ### WHERE
-###   @1=000000124.450000000 /* DECIMAL(10,5) meta=2565 nullable=1 is_null=0 */
+###   @1=124.45000 /* DECIMAL(10,5) meta=2565 nullable=1 is_null=0 */
 # at #
 #010909  4:46:40 server id 1  end_log_pos # 	Query	thread_id=#	exec_time=#	error_code=0
 SET TIMESTAMP=1000000000/*!*/;

sql/log_event.cc

@@ -2012,15 +2012,10 @@ log_event_print_value(IO_CACHE *file, const uchar *ptr,
       my_decimal dec;
       binary2my_decimal(E_DEC_FATAL_ERROR, (uchar*) ptr, &dec,
                         precision, decimals);
-      int i, end;
-      char buff[512], *pos;
-      pos= buff;
-      pos+= sprintf(buff, "%s", dec.sign() ? "-" : "");
-      end= ROUND_UP(dec.frac) + ROUND_UP(dec.intg)-1;
-      for (i=0; i < end; i++)
-        pos+= sprintf(pos, "%09d.", dec.buf[i]);
-      pos+= sprintf(pos, "%09d", dec.buf[i]);
-      my_b_printf(file, "%s", buff);
+      int length= DECIMAL_MAX_STR_LENGTH;
+      char buff[DECIMAL_MAX_STR_LENGTH + 1];
+      decimal2string(&dec, buff, &length, 0, 0, 0);
+      my_b_write(file, (uchar*)buff, length);
       my_snprintf(typestr, typestr_length, "DECIMAL(%d,%d)",
                   precision, decimals);
       return bin_size;