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java.lang.Objectcom.ibm.icu.util.UniversalTimeScale
public final class UniversalTimeScale
There are quite a few different conventions for binary datetime, depending on different
platforms and protocols. Some of these have severe drawbacks. For example, people using
Unix time (seconds since Jan 1, 1970) think that they are safe until near the year 2038.
But cases can and do arise where arithmetic manipulations causes serious problems. Consider
the computation of the average of two datetimes, for example: if one calculates them with
averageTime = (time1 + time2)/2
, there will be overflow even with dates
around the present. Moreover, even if these problems don't occur, there is the issue of
conversion back and forth between different systems.
Binary datetimes differ in a number of ways: the datatype, the unit, and the epoch (origin). We'll refer to these as time scales. For example:
Source | Datatype | Unit | Epoch |
---|---|---|---|
JAVA_TIME | long | milliseconds | Jan 1, 1970 |
UNIX_TIME | int or long | seconds | Jan 1, 1970 |
ICU4C | double | milliseconds | Jan 1, 1970 |
WINDOWS_FILE_TIME | long | ticks (100 nanoseconds) | Jan 1, 1601 |
DOTNET_DATE_TIME | long | ticks (100 nanoseconds) | Jan 1, 0001 |
MAC_OLD_TIME | int | seconds | Jan 1, 1904 |
MAC_TIME | double | seconds | Jan 1, 2001 |
EXCEL_TIME | ? | days | Dec 31, 1899 |
DB2_TIME | ? | days | Dec 31, 1899 |
All of the epochs start at 00:00 am (the earliest possible time on the day in question), and are assumed to be UTC.
The ranges for different datatypes are given in the following table (all values in years). The range of years includes the entire range expressible with positive and negative values of the datatype. The range of years for double is the range that would be allowed without losing precision to the corresponding unit.
Units | long | double | int |
---|---|---|---|
1 sec | 5.84542×10¹¹ | 285,420,920.94 | 136.10 |
1 millisecond | 584,542,046.09 | 285,420.92 | 0.14 |
1 microsecond | 584,542.05 | 285.42 | 0.00 |
100 nanoseconds (tick) | 58,454.20 | 28.54 | 0.00 |
1 nanosecond | 584.5420461 | 0.2854 | 0.00 |
This class implements a universal time scale which can be used as a 'pivot', and provide conversion functions to and from all other major time scales. This datetimes to be converted to the pivot time, safely manipulated, and converted back to any other datetime time scale.
So what to use for this pivot? Java time has plenty of range, but cannot represent
.NET framework System.DateTime
vaules without severe loss of precision. ICU4C time addresses this by using a
double
that is otherwise equivalent to the Java time. However, there are disadvantages
with doubles
. They provide for much more graceful degradation in arithmetic operations.
But they only have 53 bits of accuracy, which means that they will lose precision when
converting back and forth to ticks. What would really be nice would be a
long double
(80 bits -- 64 bit mantissa), but that is not supported on most systems.
The Unix extended time uses a structure with two components: time in seconds and a
fractional field (microseconds). However, this is clumsy, slow, and
prone to error (you always have to keep track of overflow and underflow in the
fractional field). BigDecimal
would allow for arbitrary precision and arbitrary range,
but we would not want to use this as the normal type, because it is slow and does not
have a fixed size.
Because of these issues, we ended up concluding that the .NET framework's System.DateTime
would be the
best pivot. However, we use the full range allowed by the datatype, allowing for
datetimes back to 29,000 BC and up to 29,000 AD. This time scale is very fine grained,
does not lose precision, and covers a range that will meet almost all requirements.
It will not handle the range that Java times would, but frankly, being able to handle dates
before 29,000 BC or after 29,000 AD is of very limited interest. However, for those cases,
we also allow conversion to an optional BigDecimal
format that would have arbitrary
precision and range.
Field Summary | |
---|---|
static int |
DB2_TIME
Used in DB2. |
static int |
DOTNET_DATE_TIME
Used in the .NET framework's System.DateTime structure. |
static int |
EPOCH_OFFSET_MINUS_1_VALUE
The constant used to select the epoch offset minus one value for a time scale. |
static int |
EPOCH_OFFSET_PLUS_1_VALUE
The constant used to select the epoch plus one value for a time scale. |
static int |
EPOCH_OFFSET_VALUE
The constant used to select the epoch offset value for a time scale. |
static int |
EXCEL_TIME
Used in Excel. |
static int |
FROM_MAX_VALUE
The constant used to select the maximum from value for a time scale. |
static int |
FROM_MIN_VALUE
The constant used to select the minimum from value for a time scale. |
static int |
ICU4C_TIME
Used in the ICU4C. |
static int |
JAVA_TIME
Used in the JDK. |
static int |
MAC_OLD_TIME
Used in older Macintosh systems. |
static int |
MAC_TIME
Used in the JDK. |
static int |
MAX_ROUND_VALUE
The constant used to select the maximum safe rounding value for a time scale. |
static int |
MAX_SCALE
This is the first unused time scale value. |
static int |
MAX_SCALE_VALUE
The number of time scale values. |
static int |
MIN_ROUND_VALUE
The constant used to select the minimum safe rounding value for a time scale. |
static int |
TO_MAX_VALUE
The constant used to select the maximum to value for a time scale. |
static int |
TO_MIN_VALUE
The constant used to select the minimum to value for a time scale. |
static int |
UNITS_ROUND_VALUE
The constant used to select the units round value for a time scale. |
static int |
UNITS_VALUE
The constant used to select the units value for a time scale. |
static int |
UNIX_TIME
Used in Unix systems. |
static int |
WINDOWS_FILE_TIME
Used in Windows for file times. |
Method Summary | |
---|---|
static BigDecimal |
bigDecimalFrom(BigDecimal otherTime,
int timeScale)
Convert a BigDecimal datetime from the given time scale to the universal time scale. |
static BigDecimal |
bigDecimalFrom(double otherTime,
int timeScale)
Convert a double datetime from the given time scale to the universal time scale. |
static BigDecimal |
bigDecimalFrom(long otherTime,
int timeScale)
Convert a long datetime from the given time scale to the universal time scale. |
static long |
from(long otherTime,
int timeScale)
Convert a long datetime from the given time scale to the universal time scale. |
static long |
getTimeScaleValue(int scale,
int value)
Get a value associated with a particular time scale. |
static BigDecimal |
toBigDecimal(BigDecimal universalTime,
int timeScale)
Convert a datetime from the universal time scale to a BigDecimal in the given time scale. |
static BigDecimal |
toBigDecimal(long universalTime,
int timeScale)
Convert a datetime from the universal time scale to a BigDecimal in the given time scale. |
static BigDecimal |
toBigDecimalTrunc(BigDecimal universalTime,
int timeScale)
Convert a time in the Universal Time Scale into another time scale. |
static long |
toLong(long universalTime,
int timeScale)
Convert a datetime from the universal time scale stored as a BigDecimal to a
long in the given time scale. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
---|
public static final int JAVA_TIME
long
. Value
is milliseconds since January 1, 1970.
public static final int UNIX_TIME
int
or a long
. Value
is seconds since January 1, 1970.
public static final int ICU4C_TIME
double
. Value
is milliseconds since January 1, 1970.
public static final int WINDOWS_FILE_TIME
long
. Value
is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
public static final int DOTNET_DATE_TIME
System.DateTime
structure.
Data is a long
. Value is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
public static final int MAC_OLD_TIME
int
. Value
is seconds since January 1, 1904.
public static final int MAC_TIME
double
. Value
is milliseconds since January 1, 2001.
public static final int EXCEL_TIME
?unknown?
. Value
is days since December 31, 1899.
public static final int DB2_TIME
?unknown?
. Value
is days since December 31, 1899.
public static final int MAX_SCALE
public static final int UNITS_VALUE
public static final int EPOCH_OFFSET_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int FROM_MIN_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int FROM_MAX_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int TO_MIN_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int TO_MAX_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int EPOCH_OFFSET_PLUS_1_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int EPOCH_OFFSET_MINUS_1_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int UNITS_ROUND_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int MIN_ROUND_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int MAX_ROUND_VALUE
getTimeScaleValue(int, int)
,
Constant Field Valuespublic static final int MAX_SCALE_VALUE
getTimeScaleValue(int, int)
,
Constant Field ValuesMethod Detail |
---|
public static long from(long otherTime, int timeScale)
long
datetime from the given time scale to the universal time scale.
otherTime
- The long
datetimetimeScale
- The time scale to convert from
public static BigDecimal bigDecimalFrom(double otherTime, int timeScale)
double
datetime from the given time scale to the universal time scale.
All calculations are done using BigDecimal
to guarantee that the value
does not go out of range.
otherTime
- The double
datetimetimeScale
- The time scale to convert from
public static BigDecimal bigDecimalFrom(long otherTime, int timeScale)
long
datetime from the given time scale to the universal time scale.
All calculations are done using BigDecimal
to guarantee that the value
does not go out of range.
otherTime
- The long
datetimetimeScale
- The time scale to convert from
public static BigDecimal bigDecimalFrom(BigDecimal otherTime, int timeScale)
BigDecimal
datetime from the given time scale to the universal time scale.
All calculations are done using BigDecimal
to guarantee that the value
does not go out of range.
otherTime
- The BigDecimal
datetimetimeScale
- The time scale to convert from
public static long toLong(long universalTime, int timeScale)
BigDecimal
to a
long
in the given time scale.
Since this calculation requires a divide, we must round. The straight forward
way to round by adding half of the divisor will push the sum out of range for values
within have the divisor of the limits of the precision of a long
. To get around this, we do
the rounding like this:
(universalTime - units + units/2) / units + 1
(i.e. we subtract units first to guarantee that we'll still be in range when we
add units/2
. We then need to add one to the quotent to make up for the extra subtraction.
This simplifies to:
(universalTime - units/2) / units - 1
For negative values to round away from zero, we need to flip the signs:
(universalTime + units/2) / units + 1
Since we also need to subtract the epochOffset, we fold the +/- 1
into the offset value. (i.e. epochOffsetP1
, epochOffsetM1
.)
universalTime
- The datetime in the universal time scaletimeScale
- The time scale to convert to
public static BigDecimal toBigDecimal(long universalTime, int timeScale)
BigDecimal
in the given time scale.
universalTime
- The datetime in the universal time scaletimeScale
- The time scale to convert to
public static BigDecimal toBigDecimal(BigDecimal universalTime, int timeScale)
BigDecimal
in the given time scale.
universalTime
- The datetime in the universal time scaletimeScale
- The time scale to convert to
public static long getTimeScaleValue(int scale, int value)
scale
- - the time scalevalue
- - a constant representing the value to get
public static BigDecimal toBigDecimalTrunc(BigDecimal universalTime, int timeScale)
universalTime
- the time in the Universal Time scaletimeScale
- the time scale to convert to
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