bpo-21302: Add _PyTime_AsNanoseconds() (GH-28350)

Refactor pytime.c:

* Add pytime_from_nanoseconds() and pytime_as_nanoseconds(),
  and use explicitly these functions
* Add two empty lines between functions
* PEP 7: add braces { ... }
* C99: declare variables where they are set
* Rename private functions to lowercase
* Rename error_time_t_overflow() to pytime_time_t_overflow()
* Rename win_perf_counter_frequency() to py_win_perf_counter_frequency()
* py_get_monotonic_clock(): add an assertion to detect overflow when
  mach_absolute_time() unsigned uint64_t is casted to _PyTime_t
  (signed int64_t).

_testcapi: use _PyTime_FromNanoseconds().

1 files changed, 3 insertions, 0 deletions

diff --git a/Include/cpython/pytime.h b/Include/cpython/pytime.h
index 56607d1..b045388 100644
--- a/Include/cpython/pytime.h
+++ b/Include/cpython/pytime.h
@@ -111,6 +111,9 @@ PyAPI_FUNC(_PyTime_t) _PyTime_AsMilliseconds(_PyTime_t t,
 PyAPI_FUNC(_PyTime_t) _PyTime_AsMicroseconds(_PyTime_t t,
     _PyTime_round_t round);
 
+/* Convert timestamp to a number of nanoseconds (10^-9 seconds). */
+PyAPI_FUNC(_PyTime_t) _PyTime_AsNanoseconds(_PyTime_t t);
+
 /* Convert timestamp to a number of nanoseconds (10^-9 seconds) as a Python int
    object. */
 PyAPI_FUNC(PyObject *) _PyTime_AsNanosecondsObject(_PyTime_t t);