#include "unicode/utypes.h"
Go to the source code of this file.
Typedefs | |
typedef enum UDateTimeScale | UDateTimeScale |
UDateTimeScale values are used to specify the time scale used for conversion into or out if the universal time scale. | |
typedef enum UTimeScaleValue | UTimeScaleValue |
UTimeScaleValue values are used to specify the time scale values to utmscale_getTimeScaleValue . | |
Enumerations | |
enum | UDateTimeScale { UDTS_JAVA_TIME = 0, UDTS_UNIX_TIME, UDTS_ICU4C_TIME, UDTS_WINDOWS_FILE_TIME, UDTS_DOTNET_DATE_TIME, UDTS_MAC_OLD_TIME, UDTS_MAC_TIME, UDTS_EXCEL_TIME, UDTS_DB2_TIME, UDTS_MAX_SCALE } |
UDateTimeScale values are used to specify the time scale used for conversion into or out if the universal time scale. More... | |
enum | UTimeScaleValue { UTSV_UNITS_VALUE = 0, UTSV_EPOCH_OFFSET_VALUE = 1, UTSV_FROM_MIN_VALUE = 2, UTSV_FROM_MAX_VALUE = 3, UTSV_TO_MIN_VALUE = 4, UTSV_TO_MAX_VALUE = 5, UTSV_EPOCH_OFFSET_PLUS_1_VALUE = 6, UTSV_EPOCH_OFFSET_MINUS_1_VALUE = 7, UTSV_UNITS_ROUND_VALUE = 8, UTSV_MIN_ROUND_VALUE = 9, UTSV_MAX_ROUND_VALUE = 10, UTSV_MAX_SCALE_VALUE = 11 } |
UTimeScaleValue values are used to specify the time scale values to utmscale_getTimeScaleValue . More... | |
Functions | |
int64_t | utmscale_getTimeScaleValue (UDateTimeScale timeScale, UTimeScaleValue value, UErrorCode *status) |
Get a value associated with a particular time scale. | |
int64_t | utmscale_fromInt64 (int64_t otherTime, UDateTimeScale timeScale, UErrorCode *status) |
Convert a int64_t datetime from the given time scale to the universal time scale. | |
int64_t | utmscale_toInt64 (int64_t universalTime, UDateTimeScale timeScale, UErrorCode *status) |
Convert a datetime from the universal time scale to a int64_t in the given time scale. |
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
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UDTS_JAVA_TIME | int64_t | milliseconds | Jan 1, 1970 |
UDTS_UNIX_TIME | int32_t or int64_t | seconds | Jan 1, 1970 |
UDTS_ICU4C_TIME
| double | milliseconds | Jan 1, 1970 |
UDTS_WINDOWS_FILE_TIME | int64_t
| ticks (100 nanoseconds) | Jan 1, 1601 |
UDTS_DOTNET_DATE_TIME | int64_t | ticks (100 nanoseconds)
| Jan 1, 0001 |
UDTS_MAC_OLD_TIME | int32_t or int64_t | seconds | Jan 1, 1904
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UDTS_MAC_TIME | double | seconds | Jan 1, 2001
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UDTS_EXCEL_TIME | ? | days | Dec 31, 1899 |
UDTS_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 | int64_t | double | int32_t
|
---|---|---|---|
1 sec | 5.84542x1011 | 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 |
These functions implement 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 System.DateTime
values 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 do 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 do, but frankly, being able to handle dates before 29,000 BC or after 29,000 AD is of very limited interest.
Definition in file utmscale.h.
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Definition at line 195 of file utmscale.h. |
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Definition at line 282 of file utmscale.h. |
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Convert a
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Get a value associated with a particular time scale.
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Convert a datetime from the universal time scale to a
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