//////////////////////////////////////////////////////////////////////////
// DST Calculations
//////////////////////////////////////////////////////////////////////////
/// <summary>
/// Compute the daylight savings time offset (in seconds)
/// for the specified parameters:
/// - Rule: the rule for a given year
/// - mon: month 0-11
/// - day: day 1-31
/// - weekday: 0-6
/// - time: seconds since midnight
/// </summary>
internal static int dstOffset(Rule rule, int year, int mon, int day, int time)
{
DstTime start = rule.dstStart;
DstTime end = rule.dstEnd;
if (start == null)
{
return(0);
}
int s = compare(rule, start, year, mon, day, time);
int e = compare(rule, end, year, mon, day, time);
// if end month comes earlier than start month,
// then this is dst in southern hemisphere
if (end.mon < start.mon)
{
if (e > 0 || s <= 0)
{
return(rule.dstOffset);
}
}
else
{
if (s <= 0 && e > 0)
{
return(rule.dstOffset);
}
}
return(0);
}
/// <summary>
/// Compare at time.
/// </summary>
static int compareAtTime(Rule rule, DstTime x, int time)
{
int atTime = x.atTime;
// if universal time, then we need to move atTime back to
// local time (we might cross into the previous day)
if (x.atMode == 'u')
{
if (rule.offset + x.atTime < 0)
{
atTime = 24 * 60 * 60 + rule.offset + x.atTime;
}
else
{
atTime += rule.offset;
}
}
if (atTime < time)
{
return(-1);
}
if (atTime > time)
{
return(+1);
}
return(0);
}
/// <summary>
/// Compare on day.
/// 'd' 5 the fifth of the month
/// 'l' lastSun the last Sunday in the month
/// 'l' lastMon the last Monday in the month
/// '>' Sun>=8 first Sunday on or after the eighth
/// '<' Sun<=25 last Sunday on or before the 25th (not used)
/// </summary>
static int compareOnDay(Rule rule, DstTime x, int year, int mon, int day)
{
// universal atTime might push us into the previous day
if (x.atMode == 'u' && rule.offset + x.atTime < 0)
{
++day;
}
switch (x.onMode)
{
case (byte)'d':
if (x.onDay < day)
{
return(-1);
}
if (x.onDay > day)
{
return(+1);
}
return(0);
case (byte)'l':
int last = DateTime.weekdayInMonth(year, mon, x.onWeekday, -1);
if (last < day)
{
return(-1);
}
if (last > day)
{
return(+1);
}
return(0);
case (byte)'>':
int start = DateTime.weekdayInMonth(year, mon, x.onWeekday, 1);
while (start < x.onDay)
{
start += 7;
}
if (start < day)
{
return(-1);
}
if (start > day)
{
return(+1);
}
return(0);
default:
throw new Exception("" + (char)x.onMode);
}
}
/// <summary>
/// Compare month
/// </summary>
static int compareMonth(DstTime x, int mon)
{
if (x.mon < mon)
{
return(-1);
}
if (x.mon > mon)
{
return(+1);
}
return(0);
}
/*
* static void loadIndex()
* {
* DataReader reader = new DataReader(new BufferedStream(dbFile.OpenRead()));
* try
* {
* // check magic "fantz 01"
* long magic = reader.ReadLong();
* if (magic != 0x66616e747a203031L)
* throw new IOException("Invalid magic 0x" + magic.ToString("X").ToLower());
* reader.ReadUTF();
*
* // load the name/offset pairs and verify in sort order
* int num = reader.ReadInt();
* indexNames = new string[num];
* indexTypes = new byte[num];
* indexOffsets = new int[num];
* for (int i=0; i<num; ++i)
* {
* indexNames[i] = reader.ReadUTF();
* indexTypes[i] = (byte)reader.ReadByte();
* indexOffsets[i] = reader.ReadInt();
* if (i != 0 && String.Compare(indexNames[i-1], indexNames[i], StringComparison.Ordinal) >= 0)
* throw new IOException("Index not sorted");
* }
* }
* finally
* {
* reader.Close();
* }
* }
*
* static TimeZone loadTimeZone(string name)
* {
* // find index, which maps the file offset
* int ix = Array.BinarySearch(indexNames, name);
* if (ix < 0) return null;
* int seekOffset = indexOffsets[ix];
*
* // create time zone instance
* TimeZone tz = new TimeZone();
* tz.m_name = name;
*
* // read time zone definition from database file
* FileStream f = dbFile.OpenRead();
* DataReader d = new DataReader(f);
* try
* {
* f.Seek(seekOffset, SeekOrigin.Begin);
* tz.m_name = d.ReadUTF();
* tz.m_fullName = d.ReadUTF();
* int numRules = d.ReadUnsignedShort();
* tz.rules = new Rule[numRules];
* for (int i=0; i<numRules; ++i)
* {
* Rule r = tz.rules[i] = new Rule();
* r.startYear = d.ReadUnsignedShort();
* r.offset = d.ReadInt();
* r.stdAbbr = d.ReadUTF();
* r.dstOffset = d.ReadInt();
* if (r.dstOffset == 0) continue;
* r.dstAbbr = d.ReadUTF();
* r.dstStart = loadDstTime(d);
* r.dstEnd = loadDstTime(d);
* if (i != 0 && tz.rules[i-1].startYear <= r.startYear)
* throw new IOException("TimeZone rules not sorted: " + name);
* }
* }
* finally
* {
* f.Close();
* }
* return tz;
* }
*/
static DstTime loadDstTime(DataReader d)
{
DstTime t = new DstTime();
t.mon = d.ReadByte();
t.onMode = d.ReadByte();
t.onWeekday = d.ReadByte();
t.onDay = d.ReadByte();
t.atTime = d.ReadInt();
t.atMode = d.ReadByte();
return(t);
}
/// <summary>
/// Compare the specified time to the dst start/end time.
/// Return -1 if x < specified time and +1 if x > specified time.
/// </summary>
static int compare(Rule rule, DstTime x, int year, int mon, int day, int time)
{
int c = compareMonth(x, mon);
if (c != 0)
{
return(c);
}
c = compareOnDay(rule, x, year, mon, day);
if (c != 0)
{
return(c);
}
return(compareAtTime(rule, x, time));
}
/*
static void loadIndex()
{
DataReader reader = new DataReader(new BufferedStream(dbFile.OpenRead()));
try
{
// check magic "fantz 01"
long magic = reader.ReadLong();
if (magic != 0x66616e747a203031L)
throw new IOException("Invalid magic 0x" + magic.ToString("X").ToLower());
reader.ReadUTF();
// load the name/offset pairs and verify in sort order
int num = reader.ReadInt();
indexNames = new string[num];
indexTypes = new byte[num];
indexOffsets = new int[num];
for (int i=0; i<num; ++i)
{
indexNames[i] = reader.ReadUTF();
indexTypes[i] = (byte)reader.ReadByte();
indexOffsets[i] = reader.ReadInt();
if (i != 0 && String.Compare(indexNames[i-1], indexNames[i], StringComparison.Ordinal) >= 0)
throw new IOException("Index not sorted");
}
}
finally
{
reader.Close();
}
}
static TimeZone loadTimeZone(string name)
{
// find index, which maps the file offset
int ix = Array.BinarySearch(indexNames, name);
if (ix < 0) return null;
int seekOffset = indexOffsets[ix];
// create time zone instance
TimeZone tz = new TimeZone();
tz.m_name = name;
// read time zone definition from database file
FileStream f = dbFile.OpenRead();
DataReader d = new DataReader(f);
try
{
f.Seek(seekOffset, SeekOrigin.Begin);
tz.m_name = d.ReadUTF();
tz.m_fullName = d.ReadUTF();
int numRules = d.ReadUnsignedShort();
tz.rules = new Rule[numRules];
for (int i=0; i<numRules; ++i)
{
Rule r = tz.rules[i] = new Rule();
r.startYear = d.ReadUnsignedShort();
r.offset = d.ReadInt();
r.stdAbbr = d.ReadUTF();
r.dstOffset = d.ReadInt();
if (r.dstOffset == 0) continue;
r.dstAbbr = d.ReadUTF();
r.dstStart = loadDstTime(d);
r.dstEnd = loadDstTime(d);
if (i != 0 && tz.rules[i-1].startYear <= r.startYear)
throw new IOException("TimeZone rules not sorted: " + name);
}
}
finally
{
f.Close();
}
return tz;
}
*/
static DstTime loadDstTime(DataReader d)
{
DstTime t = new DstTime();
t.mon = d.ReadByte();
t.onMode = d.ReadByte();
t.onWeekday = d.ReadByte();
t.onDay = d.ReadByte();
t.atTime = d.ReadInt();
t.atMode = d.ReadByte();
return t;
}
/// <summary>
/// Compare on day.
/// 'd' 5 the fifth of the month
/// 'l' lastSun the last Sunday in the month
/// 'l' lastMon the last Monday in the month
/// '>' Sun>=8 first Sunday on or after the eighth
/// '<' Sun<=25 last Sunday on or before the 25th (not used)
/// </summary>
static int compareOnDay(Rule rule, DstTime x, int year, int mon, int day)
{
// universal atTime might push us into the previous day
if (x.atMode == 'u' && rule.offset + x.atTime < 0)
++day;
switch (x.onMode)
{
case (byte)'d':
if (x.onDay < day) return -1;
if (x.onDay > day) return +1;
return 0;
case (byte)'l':
int last = DateTime.weekdayInMonth(year, mon, x.onWeekday, -1);
if (last < day) return -1;
if (last > day) return +1;
return 0;
case (byte)'>':
int start = DateTime.weekdayInMonth(year, mon, x.onWeekday, 1);
while (start < x.onDay) start += 7;
if (start < day) return -1;
if (start > day) return +1;
return 0;
default:
throw new Exception(""+(char)x.onMode);
}
}
/// <summary>
/// Compare month
/// </summary>
static int compareMonth(DstTime x, int mon)
{
if (x.mon < mon) return -1;
if (x.mon > mon) return +1;
return 0;
}
/// <summary>
/// Compare at time.
/// </summary>
static int compareAtTime(Rule rule, DstTime x, int time)
{
int atTime = x.atTime;
// if universal time, then we need to move atTime back to
// local time (we might cross into the previous day)
if (x.atMode == 'u')
{
if (rule.offset + x.atTime < 0)
atTime = 24*60*60 + rule.offset + x.atTime;
else
atTime += rule.offset;
}
if (atTime < time) return -1;
if (atTime > time) return +1;
return 0;
}
/// <summary>
/// Compare the specified time to the dst start/end time.
/// Return -1 if x < specified time and +1 if x > specified time.
/// </summary>
static int compare(Rule rule, DstTime x, int year, int mon, int day, int time)
{
int c = compareMonth(x, mon);
if (c != 0) return c;
c = compareOnDay(rule, x, year, mon, day);
if (c != 0) return c;
return compareAtTime(rule, x, time);
}
/// <summary>
/// Return if given date is the DstTime transition date
/// </summary>
internal static bool isDstDate(Rule rule, DstTime x, int year, int mon, int day)
{
return compareMonth(x, mon) == 0 &&
compareOnDay(rule, x, year, mon, day) == 0;
}
/// <summary>
/// Return if given date is the DstTime transition date
/// </summary>
internal static bool isDstDate(Rule rule, DstTime x, int year, int mon, int day)
{
return(compareMonth(x, mon) == 0 &&
compareOnDay(rule, x, year, mon, day) == 0);
}
