gmt2local.c revision 56893
1/* 2 * Copyright (c) 1997 3 * The Regents of the University of California. All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that: (1) source code distributions 7 * retain the above copyright notice and this paragraph in its entirety, (2) 8 * distributions including binary code include the above copyright notice and 9 * this paragraph in its entirety in the documentation or other materials 10 * provided with the distribution, and (3) all advertising materials mentioning 11 * features or use of this software display the following acknowledgement: 12 * ``This product includes software developed by the University of California, 13 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of 14 * the University nor the names of its contributors may be used to endorse 15 * or promote products derived from this software without specific prior 16 * written permission. 17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED 18 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF 19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 20 */ 21 22#ifndef lint 23static const char rcsid[] = 24 "@(#) $Header: /tcpdump/master/tcpdump/gmt2local.c,v 1.3 1999/11/21 09:36:47 fenner Exp $ (LBL)"; 25#endif 26 27#ifdef HAVE_CONFIG_H 28#include "config.h" 29#endif 30 31#include <sys/types.h> 32#include <sys/time.h> 33 34#include <stdio.h> 35#ifdef TIME_WITH_SYS_TIME 36#include <time.h> 37#endif 38 39#include "gnuc.h" 40#ifdef HAVE_OS_PROTO_H 41#include "os-proto.h" 42#endif 43 44#include "gmt2local.h" 45 46/* 47 * Returns the difference between gmt and local time in seconds. 48 * Use gmtime() and localtime() to keep things simple. 49 */ 50int32_t 51gmt2local(time_t t) 52{ 53 register int dt, dir; 54 register struct tm *gmt, *loc; 55 struct tm sgmt; 56 57 if (t == 0) 58 t = time(NULL); 59 gmt = &sgmt; 60 *gmt = *gmtime(&t); 61 loc = localtime(&t); 62 dt = (loc->tm_hour - gmt->tm_hour) * 60 * 60 + 63 (loc->tm_min - gmt->tm_min) * 60; 64 65 /* 66 * If the year or julian day is different, we span 00:00 GMT 67 * and must add or subtract a day. Check the year first to 68 * avoid problems when the julian day wraps. 69 */ 70 dir = loc->tm_year - gmt->tm_year; 71 if (dir == 0) 72 dir = loc->tm_yday - gmt->tm_yday; 73 dt += dir * 24 * 60 * 60; 74 75 return (dt); 76} 77