date: optional support for %N. Closes bug 1861.

function                                             old     new   delta
date_main                                            862    1090    +228
clock_gettime                                          -      41     +41
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 1/0 up/down: 269/0)             Total: 269 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 60 insertions, 6 deletions

diff --git a/coreutils/Config.in b/coreutils/Config.in
index ead632a31..37e885c1c 100644
--- a/coreutils/Config.in
+++ b/coreutils/Config.in
@@ -115,6 +115,13 @@ config FEATURE_DATE_ISOFMT
           Enable option (-I) to output an ISO-8601 compliant
           date/time string.
 
+config FEATURE_DATE_NANO
+        bool "Support %[num]N nanosecond format specifier"
+        default y
+        depends on DATE
+        help
+          Support %[num]N format specifier. Adds ~250 bytes of code.
+
 config FEATURE_DATE_COMPAT
         bool "Support weird 'date MMDDhhmm[[YY]YY][.ss]' format"
         default y
diff --git a/coreutils/date.c b/coreutils/date.c
index 4e5b3b0b8..c1390be76 100644
--- a/coreutils/date.c
+++ b/coreutils/date.c
@@ -84,9 +84,9 @@ static const char date_longopts[] ALIGN1 =
 int date_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int date_main(int argc UNUSED_PARAM, char **argv)
 {
+        struct timespec ts;
         struct tm tm_time;
         char buf_fmt_dt2str[64];
-        time_t tm;
         unsigned opt;
         int ifmt = -1;
         char *date_str;
@@ -161,11 +161,18 @@ int date_main(int argc UNUSED_PARAM, char **argv)
         if (opt & OPT_REFERENCE) {
                 struct stat statbuf;
                 xstat(filename, &statbuf);
-                tm = statbuf.st_mtime;
+                ts.tv_sec = statbuf.st_mtime;
+#if ENABLE_FEATURE_DATE_NANO
+                ts.tv_nsec = statbuf.st_mtimensec; //or st_atim.tv_nsec?
+#endif
         } else {
-                time(&tm);
+#if ENABLE_FEATURE_DATE_NANO
+                clock_gettime(CLOCK_REALTIME, &ts);
+#else
+                time(&ts.tv_nsec);
+#endif
         }
-        localtime_r(&tm, &tm_time);
+        localtime_r(&ts.tv_sec, &tm_time);
 
         /* If date string is given, update tm_time, and maybe set date */
         if (date_str != NULL) {
@@ -184,12 +191,12 @@ int date_main(int argc UNUSED_PARAM, char **argv)
 
                 /* Correct any day of week and day of year etc. fields */
                 tm_time.tm_isdst = -1;  /* Be sure to recheck dst */
-                tm = validate_tm_time(date_str, &tm_time);
+                ts.tv_sec = validate_tm_time(date_str, &tm_time);
 
                 maybe_set_utc(opt);
 
                 /* if setting time, set it */
-                if ((opt & OPT_SET) && stime(&tm) < 0) {
+                if ((opt & OPT_SET) && stime(&ts.tv_sec) < 0) {
                         bb_perror_msg("can't set date");
                 }
         }
@@ -222,6 +229,46 @@ int date_main(int argc UNUSED_PARAM, char **argv)
                         fmt_dt2str = (char*)"%a %b %e %H:%M:%S %Z %Y";
                 }
         }
+#if ENABLE_FEATURE_DATE_NANO
+        else {
+                /* User-specified fmt_dt2str */
+                /* Search for and process "%N" */
+                char *p = fmt_dt2str;
+                while ((p = strchr(p, '%')) != NULL) {
+                        int n, m;
+                        unsigned pres, scale;
+
+                        p++;
+                        if (*p == '%') {
+                                p++;
+                                continue;
+                        }
+                        n = strspn(p, "0123456789");
+                        if (p[n] != 'N') {
+                                p += n;
+                                continue;
+                        }
+                        /* We have "%[nnn]N" */
+                        p[-1] = '\0';
+                        p[n] = '\0';
+                        scale = 1;
+                        pres = 9;
+                        if (n) {
+                                pres = xatoi_u(p);
+                                if (pres == 0)
+                                        pres = 9;
+                                m = 9 - pres;
+                                while (--m >= 0)
+                                        scale *= 10;
+                        }
+
+                        m = p - fmt_dt2str;
+                        p += n + 1;
+                        fmt_dt2str = xasprintf("%s%0*u%s", fmt_dt2str, pres, (unsigned)ts.tv_nsec / scale, p);
+                        p = fmt_dt2str + m;
+                }
+        }
+#endif
 
 #define date_buf bb_common_bufsiz1
         if (*fmt_dt2str == '\0') {