Add conversions to and from struct timespec to module interface.

Time values are a fundamental data type, and such conversions are hard
to implement within modules because of the various forms of time
values in Emacs Lisp.  Adding dedicated conversion functions can
significantly simplify module code dealing with times.

This approach uses nanosecond precision.  While Emacs in theory has
support for higher-precision time values, in practice most languages
and standards, such as POSIX, C, Java, and Go, have settled on
nanosecond-precision integers to represent time.

* src/emacs-module.h.in: Add header for struct timespec.

* src/module-env-27.h: Add module functions for time conversion.

* src/emacs-module.c (module_extract_time, module_make_time): New
functions.
(initialize_environment): Use them.

* test/data/emacs-module/mod-test.c (Fmod_test_add_nanosecond): New
test function.
(emacs_module_init): Define it.

* test/src/emacs-module-tests.el (mod-test-add-nanosecond/valid)
(mod-test-add-nanosecond/nil, mod-test-add-nanosecond/invalid): New
unit tests.

* doc/lispref/internals.texi (Module Values): Document time
conversion functions.

1 files changed, 44 insertions, 0 deletions

diff --git a/doc/lispref/internals.texi b/doc/lispref/internals.texi
index 25892d4b57c..0e7a1339e76 100644
--- a/doc/lispref/internals.texi
+++ b/doc/lispref/internals.texi
@@ -1387,6 +1387,38 @@ This function returns the value of a Lisp float specified by
 @var{arg}, as a C @code{double} value.
 @end deftypefn
 
+@deftypefn Function struct timespec extract_time (emacs_env *@var{env}, emacs_value @var{time})
+This function, which is available since Emacs 27, interprets
+@var{time} as an Emacs Lisp time value and returns the corresponding
+@code{struct timespec}.  @xref{Time of Day}.  @code{struct timespec}
+represents a timestamp with nanosecond precision.  It has the
+following members:
+
+@table @code
+@item time_t tv_sec
+Whole number of seconds.
+@item long tv_nsec
+Fractional seconds as number of nanoseconds, always less than one
+billion.
+@end table
+
+@noindent
+@xref{Elapsed Time,,,libc}.
+
+If @var{time} has higher precision than nanoseconds, then this
+function truncates it to nanosecond precision.  This function signals
+an error if @var{time} (truncated to nanoseconds) cannot be
+represented by @code{struct timespec}.  For example, if @code{time_t}
+is a 32-bit integral type, then a @var{time} value of ten billion
+seconds would signal an error, but a @var{time} value of 600
+picoseconds would get truncated to zero.
+
+If you need to deal with time values that are not representable by
+@code{struct timespec}, or if you want higher precision, call the Lisp
+function @code{encode-time} and work with its return value.
+@xref{Time Conversion}.
+@end deftypefn
+
 @deftypefn Function bool copy_string_contents (emacs_env *@var{env}, emacs_value @var{arg}, char *@var{buf}, ptrdiff_t *@var{len})
 This function stores the UTF-8 encoded text of a Lisp string specified
 by @var{arg} in the array of @code{char} pointed by @var{buf}, which
@@ -1452,6 +1484,18 @@ This function takes a @code{double} argument @var{d} and returns the
 corresponding Emacs floating-point value.
 @end deftypefn
 
+@deftypefn Function emacs_value make_time (emacs_env *@var{env}, struct timespec @var{time})
+This function, which is available since Emacs 27, takes a @code{struct
+timespec} argument @var{time} and returns the corresponding Emacs
+timestamp as a pair @code{(@var{ticks} . @var{hz})}.  @xref{Time of
+Day}.  The return value represents exactly the same timestamp as
+@var{time}: all input values are representable, and there is never a
+loss of precision.  @code{@var{time}.tv_sec} and
+@code{@var{time}.tv_nsec} can be arbitrary values.  In particular,
+there's no requirement that @var{time} be normalized.  This means that
+@code{@var{time}.tv_nsec} can be negative or larger than 999,999,999.
+@end deftypefn
+
 @deftypefn Function emacs_value make_string (emacs_env *@var{env}, const char *@var{str}, ptrdiff_t @var{strlen})
 This function creates an Emacs string from C text string pointed by
 @var{str} whose length in bytes, not including the terminating null