1 files changed, 104 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/daynum.c b/reference/C/CONTRIB/SNIP/daynum.c
new file mode 100755
index 0000000..b2e9461
--- /dev/null
+++ b/reference/C/CONTRIB/SNIP/daynum.c
@@ -0,0 +1,104 @@
+/*
+**  DAYNUM.C - Functions to return statistics about a given date.
+**
+**  public domain by Bob Stout - uses Ray Gardner's SCALDATE.C
+*/
+
+#include "scaldate.h"
+
+static long jan1date;
+
+/*
+**  Determine if a given date is valid
+*/
+
+int valiDate(unsigned yr, unsigned mo, unsigned day)
+{
+      unsigned int days[] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+
+      if (1 > mo || 12 < mo)
+            return 0;
+      if (1 > day || day > (days[mo - 1] + (2 == mo && isleap(yr))))
+            return 0;
+      else  return 1;
+}
+
+/*
+**  Return the day of the week
+*/
+
+int dow(unsigned yr, unsigned mo, unsigned day)
+{
+ 
+#if (!ISO)        /* Sunday(0) -> Saturday(6) (i.e. U.S.) calendars  */
+      return (ymd_to_scalar(yr, mo, day) % 7L);
+#else             /* International Monday(0) -> Sunday(6) calendars  */
+      return ((ymd_to_scalar(yr, mo, day) - 1L) % 7L);
+#endif
+}
+
+/*
+**  Return the day of the year (1 - 365/6)
+*/
+
+int daynum(int year, int month, int day)
+{
+      jan1date = ymd_to_scalar(year, 1, 1);
+      return (int)(ymd_to_scalar(year, month, day) - jan1date + 1L);
+}
+
+/*
+**  Return the week of the year (1 - 52, 0 - 52 if ISO)
+*/
+
+int weeknum(int year, int month, int day)
+{
+      int wn, j1n, dn = daynum(year, month, day);
+
+      dn += (j1n = (int)((jan1date - (long)ISO) % 7L)) - 1;
+      wn = dn / 7;
+      if (ISO)
+            wn += (j1n < 4);
+      else  ++wn;
+      return wn;
+}
+
+#ifdef TEST
+
+#include <stdio.h>
+#include <stdlib.h>
+
+void do_err(void);
+
+void main(int argc, char *argv[])
+{
+      int day, month, year;
+      char *days[] =
+#if (!ISO)
+            {"Sunday", "Monday", "Tuesday", "Wednesday",
+             "Thursday", "Friday", "Saturday"};
+#else
+            {"Monday", "Tuesday", "Wednesday", "Thursday",
+             "Friday", "Saturday", "Sunday"};
+#endif
+
+      if (4 > argc)
+      {
+            puts("Usage: DAYNUM month day year");
+            return;
+      }
+
+      month = atoi(argv[1]);
+      day   = atoi(argv[2]);
+      year  = atoi(argv[3]);
+      if (100 > year)
+            year += 1900;
+
+      if (!valiDate(year, month, day))
+            printf("%d/%d/%d is invalid!\n", month, day, year);
+      else  printf("%d/%d/%d is a %s, day #%d in week %d\n", month, day, year,
+                  days[dow(year, month, day)], daynum(year, month, day),
+                  weeknum(year, month, day));
+}
+
+#endif /* TEST */