odds and sods

[tridge/junkcode.git] / tz.c

diff --git a/tz.c b/tz.c
new file mode 100644 (file)
index 0000000..b35c790
--- /dev/null
+++ b/tz.c
@@ -0,0 +1,46 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <time.h>
+
+#define TM_YEAR_BASE 1900
+
+/*******************************************************************
+yield the difference between *A and *B, in seconds, ignoring leap seconds
+********************************************************************/
+static int tm_diff(struct tm *a, struct tm *b)
+{
+  int ay = a->tm_year + (TM_YEAR_BASE - 1);
+  int by = b->tm_year + (TM_YEAR_BASE - 1);
+  int intervening_leap_days =
+    (ay/4 - by/4) - (ay/100 - by/100) + (ay/400 - by/400);
+  int years = ay - by;
+  int days = 365*years + intervening_leap_days + (a->tm_yday - b->tm_yday);
+  int hours = 24*days + (a->tm_hour - b->tm_hour);
+  int minutes = 60*hours + (a->tm_min - b->tm_min);
+  int seconds = 60*minutes + (a->tm_sec - b->tm_sec);
+
+  printf("tm_diff ay=%d by=%d ild=%d y=%d d=%d h=%d m=%d s=%d am=%d bm=%d asec=%d bsec=%d\n",
+          ay, by, intervening_leap_days, years, days, hours, minutes, seconds,
+          a->tm_min, b->tm_min,
+          a->tm_sec, b->tm_sec
+          );
+
+  if (a->tm_sec != b->tm_sec)
+         printf("Your timezone file is broken\n");
+  return seconds;
+}
+
+/*******************************************************************
+  return the UTC offset in seconds west of UTC
+  ******************************************************************/
+static int TimeZone(time_t t)
+{
+  struct tm tm_utc = *(gmtime(&t));
+  return tm_diff(&tm_utc,localtime(&t));
+}
+
+int main(int argc, char *argv[])
+{
+       TimeZone(time(NULL));
+       return 0;
+}