1 files changed, 66 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/moon_age.c b/reference/C/CONTRIB/SNIP/moon_age.c
new file mode 100755
index 0000000..e979498
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+++ b/reference/C/CONTRIB/SNIP/moon_age.c
@@ -0,0 +1,66 @@
+/* PD by Michelangelo Jones, 1:1/124. */
+
+/*
+**  Returns 0 for new moon, 15 for full moon,
+**  29 for the day before new, and so forth.
+*/
+
+/*
+**  This routine sometimes gets "off" by a few days,
+**  but is self-correcting.
+*/
+
+int moon_age(int month, int day, int year)
+{
+      static short int ages[] =
+            {18, 0, 11, 22, 3, 14, 25, 6, 17,
+             28, 9, 20, 1, 12, 23, 4, 15, 26, 7};
+      static short int offsets[] =
+            {-1, 1, 0, 1, 2, 3, 4, 5, 7, 7, 9, 9};
+
+      if (day == 31)
+            day = 1;
+      return ((ages[(year + 1) % 19] + ((day + offsets[month-1]) % 30) +
+            (year < 1900)) % 30);
+}
+
+#ifdef TEST
+
+#include <stdio.h>
+#include <stdlib.h>
+
+static char *description[] = {
+      "new",                  /* totally dark                         */
+      "waxing crescent",      /* increasing to full & quarter light   */
+      "in its first quarter", /* increasing to full & half light      */
+      "waxing gibbous",       /* increasing to full & > than half     */
+      "full",                 /* fully lighted                        */
+      "waning gibbous",       /* decreasing from full & > than half   */
+      "in its last quarter",  /* decreasing from full & half light    */
+      "waning crescent"       /* decreasing from full & quarter light */
+      };
+
+static char *months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
+                         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
+
+int main(int argc, char *argv[])
+{
+      int month, day, year, phase;
+
+      if (4 > argc)
+      {
+            puts("Usage: MOON_AGE month day year");
+            return EXIT_FAILURE;
+      }
+      month = atoi(argv[1]);
+      day   = atoi(argv[2]);
+      year  = atoi(argv[3]);
+      if (100 > year)
+            year += 1900;
+      printf("moon_age(%d, %d, %d) returned %d\n", month, day, year,
+            phase = moon_age(month, day, year));
+      printf("Moon phase on %d %s %d is %s\n", day, months[month - 1], year,
+            description[(int)((phase + 2) * 16L / 59L)]);
+}
+
+#endif /* TEST */