db: store ints as ints, not floats

DatabaseULog.write_ulog complained about wrong value types during struct
packing.

pyulog/db.py

@@ -49,7 +49,7 @@ class DatabaseULog(ULog):
     contsructor will throw an exception. See the documentation of
     "ulog_migratedb" for more information.
     '''
-    SCHEMA_VERSION = 3
+    SCHEMA_VERSION = 4
 
     @staticmethod
     def get_db_handle(db_path):

pyulog/sql/pyulog.4.sql

@@ -0,0 +1,37 @@
+BEGIN;
+PRAGMA foreign_keys=off;
+
+-- Change REAL timestamps to INT. SQLITE only supports INT64, but ULog -- changed from REAL
+-- timestamps are UINT64. We accept losing 1 bit at the top end, since 2^63
+-- microseconds = 400,000 years. which should be enough.
+
+ALTER TABLE ULog RENAME COLUMN StartTimestamp TO StartTimestamp_old;
+ALTER TABLE ULog ADD COLUMN StartTimestamp INT;
+UPDATE ULog SET StartTimestamp = CAST(StartTimestamp_old AS INT);
+
+ALTER TABLE ULog RENAME COLUMN LastTimestamp TO LastTimestamp_old;
+ALTER TABLE ULog ADD COLUMN LastTimestamp INT;
+UPDATE ULog SET LastTimestamp = CAST(LastTimestamp_old AS INT);
+
+ALTER TABLE ULogMessageDropout RENAME COLUMN Timestamp TO Timestamp_old;
+ALTER TABLE ULogMessageDropout ADD COLUMN Timestamp INT;
+UPDATE ULogMessageDropout SET Timestamp = CAST(Timestamp_old AS INT);
+
+ALTER TABLE ULogMessageDropout RENAME COLUMN Duration TO Duration_old;
+ALTER TABLE ULogMessageDropout ADD COLUMN Duration INT;
+UPDATE ULogMessageDropout SET Duration = CAST(Duration_old AS INT);
+
+ALTER TABLE ULogMessageLogging RENAME COLUMN Timestamp TO Timestamp_old;
+ALTER TABLE ULogMessageLogging ADD COLUMN Timestamp INT;
+UPDATE ULogMessageLogging SET Timestamp = CAST(Timestamp_old AS INT);
+
+ALTER TABLE ULogMessageLoggingTagged RENAME COLUMN Timestamp TO Timestamp_old;
+ALTER TABLE ULogMessageLoggingTagged ADD COLUMN Timestamp INT;
+UPDATE ULogMessageLoggingTagged SET Timestamp = CAST(Timestamp_old AS INT);
+
+ALTER TABLE ULogChangedParameter RENAME COLUMN Timestamp TO Timestamp_old;
+ALTER TABLE ULogChangedParameter ADD COLUMN Timestamp INT;
+UPDATE ULogChangedParameter SET Timestamp = CAST(Timestamp_old AS INT);
+
+PRAGMA foreign_keys=on;
+COMMIT;