hops_leap_seconds.hh File Reference

Self-contained (link-free) reimplementation of the small slice of the date library's tz facilities that HOPS actually uses: the utc/tai/gps clocks and leap-second lookup. HOPS uses ZERO timezone functionality, so the only runtime data the compiled libdate-tz supplied was the leap-second table. More...

#include <algorithm>
#include <chrono>
#include <cstdint>
#include <vector>
#include "date/date.h"

Go to the source code of this file.

Classes
struct	hops::gps_clock
	GPS clock: SI seconds since 1980-01-06; constant offset from UTC. More...
struct	hops::leap_detail::leap_entry
struct	hops::leap_second_info
	Result of a leap-second lookup, mirroring date::leap_second_info. elapsed = number of leap seconds inserted strictly before the query instant; is_leap_second = true iff the instant falls inside an inserted (23:59:60) second. More...
struct	hops::tai_clock
	TAI clock: SI seconds since 1958-01-01; constant offset from UTC. More...
struct	hops::utc_clock
	UTC clock: real SI seconds since 1970-01-01 including leap seconds. More...

Namespaces
	hops
	hops::leap_detail

Typedefs
template<class Duration >
using	hops::gps_time = std::chrono::time_point< gps_clock, Duration >
template<class Duration >
using	hops::tai_time = std::chrono::time_point< tai_clock, Duration >
template<class Duration >
using	hops::utc_time = std::chrono::time_point< utc_clock, Duration >

Functions
template<class Duration >
leap_second_info	hops::get_leap_second_info (const utc_time< Duration > &ut)
	Leap-second lookup for a utc_time, matching date::get_leap_second_info. More...
const std::vector< leap_entry > &	hops::leap_detail::leap_table ()
std::int64_t	hops::leap_detail::offset_at_sys (std::int64_t sys_seconds)

Detailed Description

Self-contained (link-free) reimplementation of the small slice of the date library's tz facilities that HOPS actually uses: the utc/tai/gps clocks and leap-second lookup. HOPS uses ZERO timezone functionality, so the only runtime data the compiled libdate-tz supplied was the leap-second table.

That table is short, well known, and last changed 2017-01-01 (CGPM Res. 4, 2022 commits to abolishing leap seconds by ~2035, so none are expected). We hardcode it here. This is so we can have: 1) no link against libdate-tz, 2) no runtime dependency on the host's /usr/share/zoneinfo (deterministic and reproducible across the manylinux / Ubuntu-LTS distribution targets), However, this is important! : the hard-coded leap second table is now our maintenance responsibility. If IERS Bulletin C ever announces a new leap second, append one entry to the events[] list in leap_table() below: the day AFTER the event and a signed delta (+1 for the usual inserted 23:59:60 second, -1 for a negative/removed leap second where 23:59:59 is skipped). TestLeapSecondDrift cross-checks the table against the installed system tz db at build time....which should catch a problem in most cases

All 27 leap seconds so far are +1; We have not had any negative leap seconds yet, but the signed representation below should in theory be able to handle either sign.

Conventions match date exactly (so results are interchangeable):

• sys_time = POSIX/std::chrono::system_clock, 86400 s/day, ignores leaps.
• utc_time = counts real SI seconds since 1970-01-01 WITH leap seconds; the leap count returned by get_leap_second_info() ranges 0..27 (the pre-1972 10 s base is folded into the tai_time constant below).
• tai_time = SI seconds since 1958-01-01; to_utc subtracts a fixed constant.
• gps_time = SI seconds since 1980-01-06; to_utc adds a fixed constant.

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Class Documentation

hops::leap_detail::leap_entry

struct hops::leap_detail::leap_entry

Class Members
int64_t	cumulative
int64_t	transition_sys

hops::leap_second_info

struct hops::leap_second_info

Result of a leap-second lookup, mirroring date::leap_second_info. elapsed = number of leap seconds inserted strictly before the query instant; is_leap_second = true iff the instant falls inside an inserted (23:59:60) second.

Class Members
seconds	elapsed
bool	is_leap_second