com.ibm.icu.util
public final class UniversalTimeScale extends Object
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.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
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(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 BigDecimal | bigDecimalFrom(BigDecimal otherTime, int timeScale)
Convert a BigDecimal 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(long universalTime, int timeScale)
Convert a datetime from the universal time scale to a BigDecimal in the given 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 | 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.
|
?unknown?
. Value
is days since December 31, 1899.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
System.DateTime
structure.
Data is a long
. Value is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN:
See Also: UniversalTimeScale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
?unknown?
. Value
is days since December 31, 1899.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
double
. Value
is milliseconds since January 1, 1970.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
long
. Value
is milliseconds since January 1, 1970.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
int
. Value
is seconds since January 1, 1904.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
double
. Value
is milliseconds since January 1, 2001.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN:
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN:
See Also: UniversalTimeScale
UNKNOWN:
See Also: UniversalTimeScale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
See Also: UniversalTimeScale
UNKNOWN:
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
int
or a long
. Value
is seconds since January 1, 1970.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
long
. Value
is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
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.
Parameters: otherTime The double
datetime timeScale The time scale to convert from
Returns: The datetime converted to the universal time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
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.
Parameters: otherTime The long
datetime timeScale The time scale to convert from
Returns: The datetime converted to the universal time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
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.
Parameters: otherTime The BigDecimal
datetime timeScale The time scale to convert from
Returns: The datetime converted to the universal time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
long
datetime from the given time scale to the universal time scale.
Parameters: otherTime The long
datetime timeScale The time scale to convert from
Returns: The datetime converted to the universal time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
Parameters: scale - the time scale value - a constant representing the value to get
Returns: - the value.
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
BigDecimal
in the given time scale.
Parameters: universalTime The datetime in the universal time scale timeScale The time scale to convert to
Returns: The datetime converted to the given time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
BigDecimal
in the given time scale.
Parameters: universalTime The datetime in the universal time scale timeScale The time scale to convert to
Returns: The datetime converted to the given time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.
Parameters: universalTime the time in the Universal Time scale timeScale the time scale to convert to
Returns: the time in the given time scale
UNKNOWN:
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
.)
Parameters: universalTime The datetime in the universal time scale timeScale The time scale to convert to
Returns: The datetime converted to the given time scale
UNKNOWN: ICU 3.2 This API might change or be removed in a future release.