mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-12-28 10:00:31 +00:00
1e7b32490d
This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).
124 lines
3.2 KiB
Go
124 lines
3.2 KiB
Go
// Package julianday provides Time to Julian day conversions.
|
|
package julianday
|
|
|
|
import (
|
|
"bytes"
|
|
"errors"
|
|
"math"
|
|
"strconv"
|
|
"time"
|
|
)
|
|
|
|
const secs_per_day = 86_400
|
|
const nsec_per_sec = 1_000_000_000
|
|
const nsec_per_day = nsec_per_sec * secs_per_day
|
|
const epoch_days = 2_440_587
|
|
const epoch_secs = secs_per_day / 2
|
|
|
|
func jd(t time.Time) (day, nsec int64) {
|
|
sec := t.Unix()
|
|
// guaranteed not to overflow
|
|
day, sec = sec/secs_per_day+epoch_days, sec%secs_per_day+epoch_secs
|
|
return day, sec*nsec_per_sec + int64(t.Nanosecond())
|
|
}
|
|
|
|
// Date returns the Julian day number for t,
|
|
// and the nanosecond offset within that day,
|
|
// in the range [0, 86399999999999].
|
|
func Date(t time.Time) (day, nsec int64) {
|
|
day, nsec = jd(t)
|
|
switch {
|
|
case nsec < 0:
|
|
day -= 1
|
|
nsec += nsec_per_day
|
|
case nsec >= nsec_per_day:
|
|
day += 1
|
|
nsec -= nsec_per_day
|
|
}
|
|
return day, nsec
|
|
}
|
|
|
|
// Float returns the Julian date for t as a float64.
|
|
//
|
|
// In the XXI century, this has submillisecond precision.
|
|
func Float(t time.Time) float64 {
|
|
day, nsec := jd(t)
|
|
// converting day and nsec to float64 is exact
|
|
return float64(day) + float64(nsec)/nsec_per_day
|
|
}
|
|
|
|
// Format returns the Julian date for t as a string.
|
|
//
|
|
// This has nanosecond precision.
|
|
func Format(t time.Time) string {
|
|
var buf [32]byte
|
|
return string(AppendFormat(buf[:0], t))
|
|
}
|
|
|
|
// AppendFormat is like Format but appends the textual representation to dst
|
|
// and returns the extended buffer.
|
|
func AppendFormat(dst []byte, t time.Time) []byte {
|
|
day, nsec := Date(t)
|
|
if day < 0 && nsec != 0 {
|
|
dst = append(dst, '-')
|
|
day = ^day
|
|
nsec = nsec_per_day - nsec
|
|
}
|
|
var buf [20]byte
|
|
dst = strconv.AppendInt(dst, day, 10)
|
|
frac := strconv.AppendFloat(buf[:0], float64(nsec)/nsec_per_day, 'f', 15, 64)
|
|
return append(dst, bytes.TrimRight(frac[1:], ".0")...)
|
|
}
|
|
|
|
// Time returns the UTC Time corresponding to the Julian day number
|
|
// and nanosecond offset within that day.
|
|
// Not all day values have a corresponding time value.
|
|
func Time(day, nsec int64) time.Time {
|
|
return time.Unix((day-epoch_days)*secs_per_day-epoch_secs, nsec).UTC()
|
|
}
|
|
|
|
// FloatTime returns the UTC Time corresponding to a Julian date.
|
|
// Not all date values have a corresponding time value.
|
|
//
|
|
// In the XXI century, this has submillisecond precision.
|
|
func FloatTime(date float64) time.Time {
|
|
day, frac := math.Modf(date)
|
|
nsec := math.Floor(frac * nsec_per_day)
|
|
return Time(int64(day), int64(nsec))
|
|
}
|
|
|
|
// Parse parses a formatted Julian date and returns the UTC Time it represents.
|
|
//
|
|
// This has nanosecond precision.
|
|
func Parse(s string) (time.Time, error) {
|
|
digits := 0
|
|
dot := len(s)
|
|
for i, b := range []byte(s) {
|
|
if '0' <= b && b <= '9' {
|
|
digits++
|
|
continue
|
|
}
|
|
if b == '.' && i < dot {
|
|
dot = i
|
|
continue
|
|
}
|
|
if (b == '+' || b == '-') && i == 0 {
|
|
continue
|
|
}
|
|
return time.Time{}, errors.New("julianday: invalid syntax")
|
|
}
|
|
if digits == 0 {
|
|
return time.Time{}, errors.New("julianday: invalid syntax")
|
|
}
|
|
|
|
day, err := strconv.ParseInt(s[:dot], 10, 64)
|
|
if err != nil && dot > 0 {
|
|
return time.Time{}, errors.New("julianday: value out of range")
|
|
}
|
|
frac, _ := strconv.ParseFloat(s[dot:], 64)
|
|
nsec := int64(math.Round(frac * nsec_per_day))
|
|
if s[0] == '-' {
|
|
nsec = -nsec
|
|
}
|
|
return Time(day, nsec), nil
|
|
}
|