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timeconv.c
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1 /*
2  * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
3  * This file is part of the GNU C Library.
4  * Contributed by Paul Eggert ([email protected]).
5  *
6  * The GNU C Library is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU Library General Public License as
8  * published by the Free Software Foundation; either version 2 of the
9  * License, or (at your option) any later version.
10  *
11  * The GNU C Library is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14  * Library General Public License for more details.
15  *
16  * You should have received a copy of the GNU Library General Public
17  * License along with the GNU C Library; see the file COPYING.LIB. If not,
18  * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19  * Boston, MA 02111-1307, USA.
20  */
21 
22 /*
23  * Converts the calendar time to broken-down time representation
24  * Based on code from glibc-2.6
25  *
26  * 2009-7-14:
27  * Moved from glibc-2.6 to kernel by Zhaolei<[email protected]>
28  */
29 
30 #include <linux/time.h>
31 #include <linux/module.h>
32 
33 /*
34  * Nonzero if YEAR is a leap year (every 4 years,
35  * except every 100th isn't, and every 400th is).
36  */
37 static int __isleap(long year)
38 {
39  return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
40 }
41 
42 /* do a mathdiv for long type */
43 static long math_div(long a, long b)
44 {
45  return a / b - (a % b < 0);
46 }
47 
48 /* How many leap years between y1 and y2, y1 must less or equal to y2 */
49 static long leaps_between(long y1, long y2)
50 {
51  long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
52  + math_div(y1 - 1, 400);
53  long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
54  + math_div(y2 - 1, 400);
55  return leaps2 - leaps1;
56 }
57 
58 /* How many days come before each month (0-12). */
59 static const unsigned short __mon_yday[2][13] = {
60  /* Normal years. */
61  {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
62  /* Leap years. */
63  {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
64 };
65 
66 #define SECS_PER_HOUR (60 * 60)
67 #define SECS_PER_DAY (SECS_PER_HOUR * 24)
68 
77 void time_to_tm(time_t totalsecs, int offset, struct tm *result)
78 {
79  long days, rem, y;
80  const unsigned short *ip;
81 
82  days = totalsecs / SECS_PER_DAY;
83  rem = totalsecs % SECS_PER_DAY;
84  rem += offset;
85  while (rem < 0) {
86  rem += SECS_PER_DAY;
87  --days;
88  }
89  while (rem >= SECS_PER_DAY) {
90  rem -= SECS_PER_DAY;
91  ++days;
92  }
93 
94  result->tm_hour = rem / SECS_PER_HOUR;
95  rem %= SECS_PER_HOUR;
96  result->tm_min = rem / 60;
97  result->tm_sec = rem % 60;
98 
99  /* January 1, 1970 was a Thursday. */
100  result->tm_wday = (4 + days) % 7;
101  if (result->tm_wday < 0)
102  result->tm_wday += 7;
103 
104  y = 1970;
105 
106  while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
107  /* Guess a corrected year, assuming 365 days per year. */
108  long yg = y + math_div(days, 365);
109 
110  /* Adjust DAYS and Y to match the guessed year. */
111  days -= (yg - y) * 365 + leaps_between(y, yg);
112  y = yg;
113  }
114 
115  result->tm_year = y - 1900;
116 
117  result->tm_yday = days;
118 
119  ip = __mon_yday[__isleap(y)];
120  for (y = 11; days < ip[y]; y--)
121  continue;
122  days -= ip[y];
123 
124  result->tm_mon = y;
125  result->tm_mday = days + 1;
126 }