gh-110850: Add PyTime_t C API (GH-115215)

* gh-110850: Add PyTime_t C API

Add PyTime_t API:

* PyTime_t type.
* PyTime_MIN and PyTime_MAX constants.
* PyTime_AsSecondsDouble(), PyTime_Monotonic(),
  PyTime_PerfCounter() and PyTime_GetSystemClock() functions.

Co-authored-by: Victor Stinner <vstinner@python.org>

Doc/c-api/time.rst

@@ -0,0 +1,83 @@
+.. highlight:: c
+
+PyTime C API
+============
+
+.. versionadded:: 3.13
+
+The clock C API provides access to system clocks.
+It is similar to the Python :mod:`time` module.
+
+For C API related to the :mod:`datetime` module, see :ref:`datetimeobjects`.
+
+
+Types
+-----
+
+.. c:type:: PyTime_t
+
+   A timestamp or duration in nanoseconds, represented as a signed 64-bit
+   integer.
+
+   The reference point for timestamps depends on the clock used. For example,
+   :c:func:`PyTime_Time` returns timestamps relative to the UNIX epoch.
+
+   The supported range is around [-292.3 years; +292.3 years].
+   Using the Unix epoch (January 1st, 1970) as reference, the supported date
+   range is around [1677-09-21; 2262-04-11].
+   The exact limits are exposed as constants:
+
+.. c:var:: PyTime_t PyTime_MIN
+
+   Minimum value of :c:type:`PyTime_t`.
+
+.. c:var:: PyTime_t PyTime_MAX
+
+   Maximum value of :c:type:`PyTime_t`.
+
+
+Clock Functions
+---------------
+
+The following functions take a pointer to a :c:expr:`PyTime_t` that they
+set to the value of a particular clock.
+Details of each clock are given in the documentation of the corresponding
+Python function.
+
+The functions return ``0`` on success, or ``-1`` (with an exception set)
+on failure.
+
+On integer overflow, they set the :c:data:`PyExc_OverflowError` exception and
+set ``*result`` to the value clamped to the ``[PyTime_MIN; PyTime_MAX]``
+range.
+(On current systems, integer overflows are likely caused by misconfigured
+system time.)
+
+As any other C API (unless otherwise specified), the functions must be called
+with the :term:`GIL` held.
+
+.. c:function:: int PyTime_Monotonic(PyTime_t *result)
+
+   Read the monotonic clock.
+   See :func:`time.monotonic` for important details on this clock.
+
+.. c:function:: int PyTime_PerfCounter(PyTime_t *result)
+
+   Read the performance counter.
+   See :func:`time.perf_counter` for important details on this clock.
+
+.. c:function:: int PyTime_Time(PyTime_t *result)
+
+   Read the “wall clock” time.
+   See :func:`time.time` for details important on this clock.
+
+
+Conversion functions
+--------------------
+
+.. c:function:: double PyTime_AsSecondsDouble(PyTime_t t)
+
+   Convert a timestamp to a number of seconds as a C :c:expr:`double`.
+
+   The function cannot fail, but note that :c:expr:`double` has limited
+   accuracy for large values.

Doc/c-api/utilities.rst

@@ -20,4 +20,5 @@ and parsing function arguments and constructing Python values from C values.
    hash.rst
    reflection.rst
    codec.rst
+   time.rst
    perfmaps.rst