Repo created

libs/base/timegm.cpp

@@ -0,0 +1,87 @@
+#include "base/timegm.hpp"
+
+#include "base/assert.hpp"
+#include "base/timer.hpp"
+
+// There are issues with this implementation due to absence
+// of time_t fromat specification. There are no guarantees
+// of its internal structure so we cannot rely on + or -.
+
+// It could be possible to substitute time_t with boost::ptime
+// in contexts where we need some arithmetical and logical operations
+// on time and we don't have to use precisely time_t.
+
+namespace
+{
+
+// Number of days elapsed since Jan 01 up to each month
+// (except for February in leap years).
+int const g_monoff[] = {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
+
+int LeapDaysCount(int y1, int y2)
+{
+  --y1;
+  --y2;
+  return (y2 / 4 - y1 / 4) - (y2 / 100 - y1 / 100) + (y2 / 400 - y1 / 400);
+}
+}  // namespace
+
+namespace base
+{
+
+int DaysOfMonth(int year, int month)
+{
+  ASSERT_GREATER_OR_EQUAL(month, 1, ());
+  ASSERT_LESS_OR_EQUAL(month, 12, ());
+
+  int const february = base::IsLeapYear(year) ? 29 : 28;
+  int const daysPerMonth[12] = {31, february, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+  return daysPerMonth[month - 1];
+}
+
+bool IsLeapYear(int year)
+{
+  return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
+}
+
+// Inspired by python's calendar.py
+time_t TimeGM(std::tm const & tm)
+{
+  int year;
+  int days;
+  int hours;
+  int minutes;
+  int seconds;
+
+  year = 1900 + tm.tm_year;
+  days = 365 * (year - 1970) + LeapDaysCount(1970, year);
+  days += g_monoff[tm.tm_mon];
+
+  if (tm.tm_mon > 1 && IsLeapYear(year))
+    ++days;
+  days += tm.tm_mday - 1;
+
+  hours = days * 24 + tm.tm_hour;
+  minutes = hours * 60 + tm.tm_min;
+  seconds = minutes * 60 + tm.tm_sec;
+
+  return base::SecondsSinceEpochToTimeT(seconds);
+}
+
+time_t TimeGM(int year, int month, int day, int hour, int min, int sec)
+{
+  ASSERT_GREATER_OR_EQUAL(month, 1, ());
+  ASSERT_LESS_OR_EQUAL(month, 12, ());
+  ASSERT_GREATER_OR_EQUAL(day, 1, ());
+  ASSERT_LESS_OR_EQUAL(day, DaysOfMonth(year, month), ());
+
+  tm t = {};
+  t.tm_year = year - 1900;
+  t.tm_mon = month - 1;
+  t.tm_mday = day;
+  t.tm_hour = hour;
+  t.tm_min = min;
+  t.tm_sec = sec;
+  return TimeGM(t);
+}
+}  // namespace base