From e3b4a8f03f3ed060abf61fdab1852bcf9dc835db Mon Sep 17 00:00:00 2001
From: Spiegel <spiegel.im.spiegel@gmail.com>
Date: Tue, 3 May 2022 09:13:01 +0900
Subject: [PATCH] Modified functions in jdn package

---
 README.md       |  4 ++--
 jdn/jdn.go      | 16 ++++++++++++++--
 jdn/jdn_test.go | 15 +++++++++++++--
 3 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index ffc21f8..879847b 100644
--- a/README.md
+++ b/README.md
@@ -262,8 +262,8 @@ func main() {
 これを実行すると以下のような結果になります。
 
 ```
-$ go run sample/sample4.go 2022-01-01
-Julian Day Number of 2022-01-01 is 2459580
+$ go run sample/sample4.go 2023-02-25
+Julian Day Number of 2023-02-25 is 2460000
 ```
 
 ## Modules Requirement Graph
diff --git a/jdn/jdn.go b/jdn/jdn.go
index 03aec3e..f0ea008 100644
--- a/jdn/jdn.go
+++ b/jdn/jdn.go
@@ -36,8 +36,8 @@ func GetMJDN(dt time.Time) int64 {
 }
 
 // FromJDN returns time.Time instance form Julian Day Number.
-func FromJD(jn int64) time.Time {
-	l := intRat(jn + 68569)
+func FromJDN(jdnum int64) time.Time {
+	l := intRat(jdnum + 68569)
 	n := floorRat(mulInt(quoInt(l, 146097), 4))
 	l = subRat(l, floorRat(quoInt(addInt(mulInt(n, 146097), 3), 4)))
 	i := floorRat(quoInt(mulInt(addInt(l, 1), 4000), 1461001))
@@ -50,6 +50,18 @@ func FromJD(jn int64) time.Time {
 	return time.Date(int(year.Num().Int64()), time.Month(int(month.Num().Int64())), int(day.Num().Int64()), 12, 0, 0, 0, time.UTC)
 }
 
+// FromJD returns time.Time instance form Julian Date.
+func FromJD(jd float64) time.Time {
+	jdnum := int64(jd)
+	dt := FromJDN(jdnum)
+	return dt.Add(time.Duration((jd - float64(jdnum)) * float64(24*time.Hour)))
+}
+
+// FromJD returns time.Time instance form Julian Date.
+func FromMJD(mjd float64) time.Time {
+	return FromJD(mjd + 2400000.5)
+}
+
 func intRat(x int64) *big.Rat {
 	return fracInt(x, 1)
 }
diff --git a/jdn/jdn_test.go b/jdn/jdn_test.go
index 4e9257b..d184f66 100644
--- a/jdn/jdn_test.go
+++ b/jdn/jdn_test.go
@@ -18,19 +18,25 @@ func TestGetJDN(t *testing.T) {
 	}{
 		{inp: time.Date(2015, time.January, 1, 0, 0, 0, 0, time.UTC), outp1: floatRat(2457023.5), outp2: 2457023, outpDt: time.Date(2015, time.January, 0, 12, 0, 0, 0, time.UTC), outp3: floatRat(57023.0), outp4: 57023},
 		{inp: time.Date(2022, time.January, 1, 0, 0, 0, 0, jst), outp1: floatRat(2459580.125), outp2: 2459580, outpDt: time.Date(2022, time.January, 0, 12, 0, 0, 0, time.UTC), outp3: floatRat(59579.625), outp4: 59579},
+		{inp: time.Date(2023, time.February, 24, 12, 0, 0, 0, time.UTC), outp1: floatRat(2460000.0), outp2: 2460000, outpDt: time.Date(2023, time.February, 24, 12, 0, 0, 0, time.UTC), outp3: floatRat(59999.5), outp4: 59999},
 	}
 	for _, tc := range testCases {
 		jd := GetJD(tc.inp)
 		if jd.Cmp(tc.outp1) != 0 {
 			t.Errorf("GetJD(%v) is %v, want %v.", tc.inp, jd.FloatString(5), tc.outp1.FloatString(5))
 		}
+		fjd, _ := jd.Float64()
+		dt := FromJD(fjd)
+		if !dt.Equal(tc.inp) {
+			t.Errorf("FromJD(%v) is %v, want %v.", fjd, dt, tc.inp)
+		}
 		jn := GetJDN(tc.inp)
 		if jn != tc.outp2 {
 			t.Errorf("GetJDN(%v) is %v, want %v.", tc.inp, jn, tc.outp2)
 		}
-		dt := FromJD(jn)
+		dt = FromJDN(jn)
 		if !dt.Equal(tc.outpDt) {
-			t.Errorf("FromJD(%v) is %v, want %v.", jn, dt, tc.outpDt)
+			t.Errorf("FromJDN(%v) is %v, want %v.", jn, dt, tc.outpDt)
 		}
 		mjd := GetMJD(tc.inp)
 		if mjd.Cmp(tc.outp3) != 0 {
@@ -40,6 +46,11 @@ func TestGetJDN(t *testing.T) {
 		if mjdn != tc.outp4 {
 			t.Errorf("GetMJDN(%v) is %v, want %v.", tc.inp, mjdn, tc.outp4)
 		}
+		fmjd, _ := mjd.Float64()
+		dt = FromMJD(fmjd)
+		if !dt.Equal(tc.inp) {
+			t.Errorf("FromMJD(%v) is %v, want %v.", fjd, dt, tc.inp)
+		}
 	}
 }