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 | *
|---|---|---|---|
| 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 | * *
| UDTS_MAC_TIME | *double | *seconds | *Jan 1, 2001 | *
| 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.
*
*/
/**
* UDateTimeScale values are used to specify the time scale used for
* conversion into or out if the universal time scale.
*
* @stable ICU 3.2
*/
typedef enum UDateTimeScale {
/**
* Used in the JDK. Data is a Java long (int64_t). Value
* is milliseconds since January 1, 1970.
*
* @stable ICU 3.2
*/
UDTS_JAVA_TIME = 0,
/**
* Used on Unix systems. Data is int32_t or int64_t. Value
* is seconds since January 1, 1970.
*
* @stable ICU 3.2
*/
UDTS_UNIX_TIME,
/**
* Used in IUC4C. Data is a double. Value
* is milliseconds since January 1, 1970.
*
* @stable ICU 3.2
*/
UDTS_ICU4C_TIME,
/**
* Used in Windows for file times. Data is an int64_t. Value
* is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
*
* @stable ICU 3.2
*/
UDTS_WINDOWS_FILE_TIME,
/**
* Used in the .NET framework's System.DateTime structure. Data is an int64_t. Value
* is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
*
* @stable ICU 3.2
*/
UDTS_DOTNET_DATE_TIME,
/**
* Used in older Macintosh systems. Data is int32_t or int64_t. Value
* is seconds since January 1, 1904.
*
* @stable ICU 3.2
*/
UDTS_MAC_OLD_TIME,
/**
* Used in newer Macintosh systems. Data is a double. Value
* is seconds since January 1, 2001.
*
* @stable ICU 3.2
*/
UDTS_MAC_TIME,
/**
* Used in Excel. Data is an ?unknown?. Value
* is days since December 31, 1899.
*
* @stable ICU 3.2
*/
UDTS_EXCEL_TIME,
/**
* Used in DB2. Data is an ?unknown?. Value
* is days since December 31, 1899.
*
* @stable ICU 3.2
*/
UDTS_DB2_TIME,
/**
* The first unused time scale value. The limit of this enum
*/
UDTS_MAX_SCALE
} UDateTimeScale;
/**
* UTimeScaleValue values are used to specify the time scale values
* to utmscale_getTimeScaleValue.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
typedef enum UTimeScaleValue {
/**
* The constant used to select the units vale
* for a time scale.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
UTSV_UNITS_VALUE = 0,
/**
* The constant used to select the epoch offset value
* for a time scale.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
UTSV_EPOCH_OFFSET_VALUE=1,
/**
* The constant used to select the minimum from value
* for a time scale.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
UTSV_FROM_MIN_VALUE=2,
/**
* The constant used to select the maximum from value
* for a time scale.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
UTSV_FROM_MAX_VALUE=3,
/**
* The constant used to select the minimum to value
* for a time scale.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
UTSV_TO_MIN_VALUE=4,
/**
* The constant used to select the maximum to value
* for a time scale.
*
* @see utmscale_getTimeScaleValue
*
* @stable ICU 3.2
*/
UTSV_TO_MAX_VALUE=5,
#ifndef U_HIDE_INTERNAL_API
/**
* The constant used to select the epoch plus one value
* for a time scale.
*
* NOTE: This is an internal value. DO NOT USE IT. May not
* actually be equal to the epoch offset value plus one.
*
* @see utmscale_getTimeScaleValue
*
* @internal ICU 3.2
*/
UTSV_EPOCH_OFFSET_PLUS_1_VALUE=6,
/**
* The constant used to select the epoch plus one value
* for a time scale.
*
* NOTE: This is an internal value. DO NOT USE IT. May not
* actually be equal to the epoch offset value plus one.
*
* @see utmscale_getTimeScaleValue
*
* @internal ICU 3.2
*/
UTSV_EPOCH_OFFSET_MINUS_1_VALUE=7,
/**
* The constant used to select the units round value
* for a time scale.
*
* NOTE: This is an internal value. DO NOT USE IT.
*
* @see utmscale_getTimeScaleValue
*
* @internal ICU 3.2
*/
UTSV_UNITS_ROUND_VALUE=8,
/**
* The constant used to select the minimum safe rounding value
* for a time scale.
*
* NOTE: This is an internal value. DO NOT USE IT.
*
* @see utmscale_getTimeScaleValue
*
* @internal ICU 3.2
*/
UTSV_MIN_ROUND_VALUE=9,
/**
* The constant used to select the maximum safe rounding value
* for a time scale.
*
* NOTE: This is an internal value. DO NOT USE IT.
*
* @see utmscale_getTimeScaleValue
*
* @internal ICU 3.2
*/
UTSV_MAX_ROUND_VALUE=10,
#endif /* U_HIDE_INTERNAL_API */
/**
* The number of time scale values, in other words limit of this enum.
*
* @see utmscale_getTimeScaleValue
*/
UTSV_MAX_SCALE_VALUE=11
} UTimeScaleValue;
/**
* Get a value associated with a particular time scale.
*
* @param timeScale The time scale
* @param value A constant representing the value to get
* @param status The status code. Set to U_ILLEGAL_ARGUMENT_ERROR if arguments are invalid.
* @return - the value.
*
* @stable ICU 3.2
*/
U_STABLE int64_t U_EXPORT2
utmscale_getTimeScaleValue(UDateTimeScale timeScale, UTimeScaleValue value, UErrorCode *status);
/* Conversion to 'universal time scale' */
/**
* Convert a int64_t datetime from the given time scale to the universal time scale.
*
* @param otherTime The int64_t datetime
* @param timeScale The time scale to convert from
* @param status The status code. Set to U_ILLEGAL_ARGUMENT_ERROR if the conversion is out of range.
*
* @return The datetime converted to the universal time scale
*
* @stable ICU 3.2
*/
U_STABLE int64_t U_EXPORT2
utmscale_fromInt64(int64_t otherTime, UDateTimeScale timeScale, UErrorCode *status);
/* Conversion from 'universal time scale' */
/**
* Convert a datetime from the universal time scale to a int64_t in the given time scale.
*
* @param universalTime The datetime in the universal time scale
* @param timeScale The time scale to convert to
* @param status The status code. Set to U_ILLEGAL_ARGUMENT_ERROR if the conversion is out of range.
*
* @return The datetime converted to the given time scale
*
* @stable ICU 3.2
*/
U_STABLE int64_t U_EXPORT2
utmscale_toInt64(int64_t universalTime, UDateTimeScale timeScale, UErrorCode *status);
#endif /* #if !UCONFIG_NO_FORMATTING */
#endif