Add Julian day conversion function.

Makefile

@@ -13,4 +13,7 @@ CGOFILES=\
 	trace.go\
 	blob.go
 
+GOFILES=\
+	date.go
+
 include $(GOROOT)/src/Make.pkg

date.go

+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package sqlite provides access to the SQLite library, version 3.
+
+package sqlite
+
+import (
+	"time"
+)
+
+const (
+	JULIAN_DAY         = 2440587.5 // 1970-01-01 00:00:00 is JD 2440587.5
+	DAY_IN_NANOSECONDS = 60 * 60 * 24 * 10E6
+)
+
+func JulianDayToUTC(jd float64) *time.Time {
+	jd -= JULIAN_DAY
+	jd *= DAY_IN_NANOSECONDS
+	return time.NanosecondsToUTC(int64(jd))
+}
+func JulianDayToLocalTime(jd float64) *time.Time {
+	jd -= JULIAN_DAY
+	jd *= DAY_IN_NANOSECONDS
+	return time.NanosecondsToLocalTime(int64(jd))
+}
+
+func JulianDay(t *time.Time) float64 {
+	ns := float64(t.Nanoseconds())
+	if ns >= 0 {
+		ns += 0.5
+	}
+	return ns/DAY_IN_NANOSECONDS + JULIAN_DAY
+}

date_test.go

+package sqlite
+
+import (
+	"testing"
+	"time"
+)
+
+func TestJulianDay(t *testing.T) {
+	utc := JulianDayToUTC(JULIAN_DAY)
+	if utc.Nanoseconds() != 0 {
+		t.Errorf("Error, expecting %d got %d", 0, utc.Nanoseconds())
+	}
+	now := time.LocalTime()
+	r := JulianDayToLocalTime(JulianDay(now))
+	if r.Nanoseconds()/10000 != now.Nanoseconds()/10000 { // FIXME Rounding problem?
+		t.Errorf("%#v <> %#v", now, r)
+	}
+}

sqlite.go

@@ -384,6 +384,8 @@ func (s *Stmt) Exec(args ...interface{}) os.Error {
 	return nil
 }
 
+// Don't use it with SELECT or anything that returns data.
+// Like Exec but returns the number of rows that were changed or inserted or deleted.
 func (s *Stmt) ExecUpdate(args ...interface{}) (int, os.Error) {
 	err := s.Exec(args...)
 	if err != nil {