File wfm_time.h¶

FileList > inc > wfm > wfm_time.h

#include <stdint.h>

Public Static Functions¶

Type	Name
int	wfm_j1950_to_unix_ns (double t_j1950, uint64_t * out_ns)
double	wfm_j1950_to_unix_sec (double t_j1950)
int	wfm_timecode_is_set (double timecode)
double	wfm_unix_to_j1950_sec (double t_unix)

Macros¶

Type	Name
define	WFM_J1950_UNIX_OFFSET_SEC `631152000.0`
define	WFM_TIMECODE_UNSET `0.0`

Public Static Functions Documentation¶

function wfm_j1950_to_unix_ns¶

static inline int wfm_j1950_to_unix_ns (
    double t_j1950,
    uint64_t * out_ns
)

Convert a BLUE timecode to UNIX nanoseconds, the form dp_sample_clock_track() takes.

Fails rather than wrapping for the two cases a uint64_t cannot express: an unset timecode, and any instant before 1970. A 1950s capture is real BLUE data, so this returning nonzero is a normal answer, not an error to paper over — the caller has an epoch it simply cannot hand to the sample clock.

Note:

Nanosecond precision is not available from BLUE. The timecode is a double of seconds, so near the present its own resolution is about half a microsecond (2^-52 * 2^31). The nanosecond result is exact arithmetic on an input that is not itself nanosecond-accurate; treat the bottom three digits as padding.

Parameters:

t_j1950 Seconds since 1950-01-01T00:00:00Z.
out_ns Receives nanoseconds since the UNIX epoch; untouched on failure.

Returns:

0 on success, -1 if the timecode is unset or predates 1970.

function wfm_j1950_to_unix_sec¶

static inline double wfm_j1950_to_unix_sec (
    double t_j1950
)

Convert a BLUE timecode to seconds since the UNIX epoch.

No range check: the result is simply shifted, and a pre-1970 capture is a legitimate negative. Guard with wfm_timecode_is_set first if a zero would be meaningless to the caller.

Parameters:

t_j1950 Seconds since 1950-01-01T00:00:00Z.

Returns:

Seconds since 1970-01-01T00:00:00Z.

function wfm_timecode_is_set¶

static inline int wfm_timecode_is_set (
    double timecode
)

Nonzero if timecode carries a real capture time.

Parameters:

timecode Raw BLUE header timecode, J1950 seconds.

function wfm_unix_to_j1950_sec¶

static inline double wfm_unix_to_j1950_sec (
    double t_unix
)

Convert seconds since the UNIX epoch to a BLUE timecode.

Parameters:

t_unix Seconds since 1970-01-01T00:00:00Z.

Returns:

Seconds since 1950-01-01T00:00:00Z.

Macro Definition Documentation¶

define WFM_J1950_UNIX_OFFSET_SEC¶

#define WFM_J1950_UNIX_OFFSET_SEC `631152000.0`

Seconds from the J1950 epoch to the UNIX epoch.

20 years, of which 1952/56/60/64/68 were leap: 20*365 + 5 = 7305 days, 7305 * 86400 = 631152000.

define WFM_TIMECODE_UNSET¶

#define WFM_TIMECODE_UNSET `0.0`

The value a BLUE header carries when nothing set a capture time.

A zero timecode is "unset", not 1950-01-01. doppler's own writer leaves the field zero (wfm_writer_core.c zeroes bytes 54-96), and so do many producers, so converting a zero straight through would date every such capture to 1950 — confidently, and wrongly. Same ambiguity wfm_fc_source_t exists to resolve for centre frequency: ask whether it was set before trusting what it says.

The documentation for this class was generated from the following file native/inc/wfm/wfm_time.h