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 (eggert@twinsun.com). 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<zhaolei@cn.fujitsu.com> 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 69 /** 70 * time_to_tm - converts the calendar time to local broken-down time 71 * 72 * @totalsecs the number of seconds elapsed since 00:00:00 on January 1, 1970, 73 * Coordinated Universal Time (UTC). 74 * @offset offset seconds adding to totalsecs. 75 * @result pointer to struct tm variable to receive broken-down time 76 */ 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 } 127 EXPORT_SYMBOL(time_to_tm); 128