Initial revision

1 files changed, 259 insertions, 0 deletions

diff --git a/libc/misc/time/mktime.c b/libc/misc/time/mktime.c
new file mode 100644
index 000000000..7f7aabcd7
--- /dev/null
+++ b/libc/misc/time/mktime.c
@@ -0,0 +1,259 @@
+
+/* This is adapted from glibc */
+/* Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc. */
+
+
+/* Assume that leap seconds are possible, unless told otherwise.
+   If the host has a `zic' command with a -L leapsecondfilename' option,
+   then it supports leap seconds; otherwise it probably doesn't.  */
+#ifndef LEAP_SECONDS_POSSIBLE
+#define LEAP_SECONDS_POSSIBLE 1
+#endif
+
+#include <sys/types.h>          /* Some systems define `time_t' here.  */
+#include <time.h>
+
+#if __STDC__ || __GNU_LIBRARY__ || STDC_HEADERS
+#include <limits.h>
+#endif
+
+#if DEBUG
+#include <stdio.h>
+#if __STDC__ || __GNU_LIBRARY__ || STDC_HEADERS
+#include <stdlib.h>
+#endif
+/* Make it work even if the system's libc has its own mktime routine.  */
+#define mktime my_mktime
+#endif /* DEBUG */
+
+#ifndef __P
+#if defined (__GNUC__) || (defined (__STDC__) && __STDC__)
+#define __P(args) args
+#else
+#define __P(args) ()
+#endif  /* GCC.  */
+#endif  /* Not __P.  */
+
+#ifndef CHAR_BIT
+#define CHAR_BIT 8
+#endif
+
+#ifndef INT_MIN
+#define INT_MIN (~0 << (sizeof (int) * CHAR_BIT - 1))
+#endif
+#ifndef INT_MAX
+#define INT_MAX (~0 - INT_MIN)
+#endif
+
+#ifndef TIME_T_MIN
+#define TIME_T_MIN (0 < (time_t) -1 ? (time_t) 0 \
+                    : ~ (time_t) 0 << (sizeof (time_t) * CHAR_BIT - 1))
+#endif
+#ifndef TIME_T_MAX
+#define TIME_T_MAX (~ (time_t) 0 - TIME_T_MIN)
+#endif
+
+#define TM_YEAR_BASE 1900
+#define EPOCH_YEAR 1970
+
+#ifndef __isleap
+/* Nonzero if YEAR is a leap year (every 4 years,
+   except every 100th isn't, and every 400th is).  */
+#define __isleap(year)  \
+  ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0))
+#endif
+
+/* How many days come before each month (0-12).  */
+const unsigned short int __mon_yday[2][13] =
+  {
+    /* Normal years.  */
+    { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 },
+    /* Leap years.  */
+    { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 }
+  };
+
+static time_t ydhms_tm_diff __P ((int, int, int, int, int, const struct tm *));
+time_t __mktime_internal __P ((struct tm *,
+                               struct tm *(*) (const time_t *, struct tm *),
+                               time_t *));
+
+/* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP),
+   measured in seconds, ignoring leap seconds.
+   YEAR uses the same numbering as TM->tm_year.
+   All values are in range, except possibly YEAR.
+   If overflow occurs, yield the low order bits of the correct answer.  */
+static time_t
+ydhms_tm_diff (year, yday, hour, min, sec, tp)
+     int year, yday, hour, min, sec;
+     const struct tm *tp;
+{
+  /* Compute intervening leap days correctly even if year is negative.
+     Take care to avoid int overflow.  time_t overflow is OK, since
+     only the low order bits of the correct time_t answer are needed.
+     Don't convert to time_t until after all divisions are done, since
+     time_t might be unsigned.  */
+  int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3);
+  int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3);
+  int a100 = a4 / 25 - (a4 % 25 < 0);
+  int b100 = b4 / 25 - (b4 % 25 < 0);
+  int a400 = a100 >> 2;
+  int b400 = b100 >> 2;
+  int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400);
+  time_t years = year - (time_t) tp->tm_year;
+  time_t days = (365 * years + intervening_leap_days
+                 + (yday - tp->tm_yday));
+  return (60 * (60 * (24 * days + (hour - tp->tm_hour))
+                + (min - tp->tm_min))
+          + (sec - tp->tm_sec));
+}
+
+
+static time_t localtime_offset;
+
+
+/* Convert *TP to a time_t value.  */
+time_t
+mktime (tp)
+     struct tm *tp;
+{
+#ifdef _LIBC
+  /* POSIX.1 8.1.1 requires that whenever mktime() is called, the
+     time zone names contained in the external variable `tzname' shall
+     be set as if the tzset() function had been called.  */
+  __tzset ();
+#endif
+
+  return __mktime_internal (tp, localtime_r, &localtime_offset);
+}
+
+/* Convert *TP to a time_t value, inverting
+   the monotonic and mostly-unit-linear conversion function CONVERT.
+   Use *OFFSET to keep track of a guess at the offset of the result,
+   compared to what the result would be for UTC without leap seconds.
+   If *OFFSET's guess is correct, only one CONVERT call is needed.  */
+time_t
+__mktime_internal (tp, convert, offset)
+     struct tm *tp;
+     struct tm *(*convert) __P ((const time_t *, struct tm *));
+     time_t *offset;
+{
+  time_t t, dt, t0;
+  struct tm tm;
+
+  /* The maximum number of probes (calls to CONVERT) should be enough
+     to handle any combinations of time zone rule changes, solar time,
+     and leap seconds.  Posix.1 prohibits leap seconds, but some hosts
+     have them anyway.  */
+  int remaining_probes = 4;
+
+  /* Time requested.  Copy it in case CONVERT modifies *TP; this can
+     occur if TP is localtime's returned value and CONVERT is localtime.  */
+  int sec = tp->tm_sec;
+  int min = tp->tm_min;
+  int hour = tp->tm_hour;
+  int mday = tp->tm_mday;
+  int mon = tp->tm_mon;
+  int year_requested = tp->tm_year;
+  int isdst = tp->tm_isdst;
+
+  /* Ensure that mon is in range, and set year accordingly.  */
+  int mon_remainder = mon % 12;
+  int negative_mon_remainder = mon_remainder < 0;
+  int mon_years = mon / 12 - negative_mon_remainder;
+  int year = year_requested + mon_years;
+
+  /* The other values need not be in range:
+     the remaining code handles minor overflows correctly,
+     assuming int and time_t arithmetic wraps around.
+     Major overflows are caught at the end.  */
+
+  /* Calculate day of year from year, month, and day of month.
+     The result need not be in range.  */
+  int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)]
+               [mon_remainder + 12 * negative_mon_remainder])
+              + mday - 1);
+
+#if LEAP_SECONDS_POSSIBLE
+  /* Handle out-of-range seconds specially,
+     since ydhms_tm_diff assumes every minute has 60 seconds.  */
+  int sec_requested = sec;
+  if (sec < 0)
+    sec = 0;
+  if (59 < sec)
+    sec = 59;
+#endif
+
+  /* Invert CONVERT by probing.  First assume the same offset as last time.
+     Then repeatedly use the error to improve the guess.  */
+
+  tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE;
+  tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0;
+  t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm);
+
+  for (t = t0 + *offset;
+       (dt = ydhms_tm_diff (year, yday, hour, min, sec, (*convert) (&t, &tm)));
+       t += dt)
+    if (--remaining_probes == 0)
+      return -1;
+
+  /* Check whether tm.tm_isdst has the requested value, if any.  */
+  if (0 <= isdst && 0 <= tm.tm_isdst)
+    {
+      int dst_diff = (isdst != 0) - (tm.tm_isdst != 0);
+      if (dst_diff)
+        {
+          /* Move two hours in the direction indicated by the disagreement,
+             probe some more, and switch to a new time if found.
+             The largest known fallback due to daylight savings is two hours:
+             once, in Newfoundland, 1988-10-30 02:00 -> 00:00.  */
+          time_t ot = t - 2 * 60 * 60 * dst_diff;
+          while (--remaining_probes != 0)
+            {
+              struct tm otm;
+              if (! (dt = ydhms_tm_diff (year, yday, hour, min, sec,
+                                         (*convert) (&ot, &otm))))
+                {
+                  t = ot;
+                  tm = otm;
+                  break;
+                }
+              if ((ot += dt) == t)
+                break;  /* Avoid a redundant probe.  */
+            }
+        }
+    }
+
+  *offset = t - t0;
+
+#if LEAP_SECONDS_POSSIBLE
+  if (sec_requested != tm.tm_sec)
+    {
+      /* Adjust time to reflect the tm_sec requested, not the normalized value.
+         Also, repair any damage from a false match due to a leap second.  */
+      t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60);
+      (*convert) (&t, &tm);
+    }
+#endif
+
+#if 0
+  if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3)
+    {
+      /* time_t isn't large enough to rule out overflows in ydhms_tm_diff,
+         so check for major overflows.  A gross check suffices,
+         since if t has overflowed, it is off by a multiple of
+         TIME_T_MAX - TIME_T_MIN + 1.  So ignore any component of
+         the difference that is bounded by a small value.  */
+
+      double dyear = (double) year_requested + mon_years - tm.tm_year;
+      double dday = 366 * dyear + mday;
+      double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested;
+
+      if (TIME_T_MAX / 3 - TIME_T_MIN / 3 < (dsec < 0 ? - dsec : dsec))
+        return -1;
+    }
+#endif
+
+  *tp = tm;
+  return t;
+}
+