GRASS Programmer's Manual  6.4.3(2013)-r
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tz2.c
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1 /*
2  * Copyright (C) 1995. Bill Brown <brown@gis.uiuc.edu> & Michael Shapiro
3  *
4  * This program is free software under the GPL (>=v2)
5  * Read the file GPL.TXT coming with GRASS for details.
6  */
7 #include <grass/datetime.h>
8 
9 
24 int datetime_change_timezone(DateTime * dt, int minutes)
25 { /* new timezone in minutes */
26  int stat;
27  int old_minutes, diff_minutes;
28  DateTime incr;
29 
30  stat = datetime_get_timezone(dt, &old_minutes);
31  if (stat != 0)
32  return stat;
33  if (!datetime_is_valid_timezone(minutes))
34  return datetime_error(-4, "invalid datetime timezone");
35 
36  /* create a relative minute increment */
37  datetime_set_type(&incr, DATETIME_RELATIVE, DATETIME_MINUTE,
38  DATETIME_MINUTE, 0);
39 
40  /* BB - needed to set SIGN here */
41  diff_minutes = minutes - old_minutes;
42  if (diff_minutes >= 0) {
43  datetime_set_minute(&incr, diff_minutes);
44  }
45  else {
46  datetime_invert_sign(&incr);
47  datetime_set_minute(&incr, -diff_minutes);
48  }
49 
50  return datetime_increment(dt, &incr);
51 }
52 
53 
63 int datetime_change_to_utc(DateTime * dt)
64 {
65  return datetime_change_timezone(dt, 0);
66 }
67 
68 
87 void datetime_decompose_timezone(int tz, int *hours, int *minutes)
88 {
89  if (tz < 0)
90  tz = -tz;
91 
92  *hours = tz / 60;
93  *minutes = tz % 60;
94 }