1 // SPDX-License-Identifier: LGPL-2.0+ 2 /* 3 * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc. 4 * This file is part of the GNU C Library. 5 * Contributed by Paul Eggert (eggert@twinsun.com). 6 * 7 * The GNU C Library is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Library General Public License as 9 * published by the Free Software Foundation; either version 2 of the 10 * License, or (at your option) any later version. 11 * 12 * The GNU C Library is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Library General Public License for more details. 16 * 17 * You should have received a copy of the GNU Library General Public 18 * License along with the GNU C Library; see the file COPYING.LIB. If not, 19 * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, 20 * Boston, MA 02111-1307, USA. 21 */ 22 23 /* 24 * Converts the calendar time to broken-down time representation 25 * Based on code from glibc-2.6 26 * 27 * 2009-7-14: 28 * Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com> 29 */ 30 31 #include <linux/time.h> 32 #include <linux/module.h> 33 34 /* 35 * Nonzero if YEAR is a leap year (every 4 years, 36 * except every 100th isn't, and every 400th is). 37 */ 38 static int __isleap(long year) 39 { 40 return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0); 41 } 42 43 /* do a mathdiv for long type */ 44 static long math_div(long a, long b) 45 { 46 return a / b - (a % b < 0); 47 } 48 49 /* How many leap years between y1 and y2, y1 must less or equal to y2 */ 50 static long leaps_between(long y1, long y2) 51 { 52 long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100) 53 + math_div(y1 - 1, 400); 54 long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100) 55 + math_div(y2 - 1, 400); 56 return leaps2 - leaps1; 57 } 58 59 /* How many days come before each month (0-12). */ 60 static const unsigned short __mon_yday[2][13] = { 61 /* Normal years. */ 62 {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365}, 63 /* Leap years. */ 64 {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366} 65 }; 66 67 #define SECS_PER_HOUR (60 * 60) 68 #define SECS_PER_DAY (SECS_PER_HOUR * 24) 69 70 /** 71 * time64_to_tm - converts the calendar time to local broken-down time 72 * 73 * @totalsecs the number of seconds elapsed since 00:00:00 on January 1, 1970, 74 * Coordinated Universal Time (UTC). 75 * @offset offset seconds adding to totalsecs. 76 * @result pointer to struct tm variable to receive broken-down time 77 */ 78 void time64_to_tm(time64_t totalsecs, int offset, struct tm *result) 79 { 80 long days, rem, y; 81 int remainder; 82 const unsigned short *ip; 83 84 days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder); 85 rem = remainder; 86 rem += offset; 87 while (rem < 0) { 88 rem += SECS_PER_DAY; 89 --days; 90 } 91 while (rem >= SECS_PER_DAY) { 92 rem -= SECS_PER_DAY; 93 ++days; 94 } 95 96 result->tm_hour = rem / SECS_PER_HOUR; 97 rem %= SECS_PER_HOUR; 98 result->tm_min = rem / 60; 99 result->tm_sec = rem % 60; 100 101 /* January 1, 1970 was a Thursday. */ 102 result->tm_wday = (4 + days) % 7; 103 if (result->tm_wday < 0) 104 result->tm_wday += 7; 105 106 y = 1970; 107 108 while (days < 0 || days >= (__isleap(y) ? 366 : 365)) { 109 /* Guess a corrected year, assuming 365 days per year. */ 110 long yg = y + math_div(days, 365); 111 112 /* Adjust DAYS and Y to match the guessed year. */ 113 days -= (yg - y) * 365 + leaps_between(y, yg); 114 y = yg; 115 } 116 117 result->tm_year = y - 1900; 118 119 result->tm_yday = days; 120 121 ip = __mon_yday[__isleap(y)]; 122 for (y = 11; days < ip[y]; y--) 123 continue; 124 days -= ip[y]; 125 126 result->tm_mon = y; 127 result->tm_mday = days + 1; 128 } 129 EXPORT_SYMBOL(time64_to_tm); 130