* 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: * * *

Table 1: Binary Time Scales *
SourceDatatypeUnitEpoch
UDTS_JAVA_TIMEint64_tmillisecondsJan 1, 1970
UDTS_UNIX_TIMEint32_t or int64_tsecondsJan 1, 1970
UDTS_ICU4C_TIMEdoublemillisecondsJan 1, 1970
UDTS_WINDOWS_FILE_TIMEint64_tticks (100 nanoseconds)Jan 1, 1601
UDTS_DOTNET_DATE_TIMEint64_tticks (100 nanoseconds)Jan 1, 0001
UDTS_MAC_OLD_TIMEint32_t or int64_tsecondsJan 1, 1904
UDTS_MAC_TIMEdoublesecondsJan 1, 2001
UDTS_EXCEL_TIME?daysDec 31, 1899
UDTS_DB2_TIME?daysDec 31, 1899
UDTS_UNIX_MICROSECONDS_TIMEint64_tmicrosecondsJan 1, 1970
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

* 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. * * *

Unitsint64_tdoubleint32_t
1 sec5.84542x1011285,420,920.94136.10
1 millisecond584,542,046.09285,420.920.14
1 microsecond584,542.05285.420.00
100 nanoseconds (tick)58,454.2028.540.00
1 nanosecond584.54204610.28540.00
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

* 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, /** * Data is a long. Value is microseconds since January 1, 1970. * Similar to Unix time (linear value from 1970) and struct timeval * (microseconds resolution). * * @stable ICU 3.8 */ UDTS_UNIX_MICROSECONDS_TIME, #ifndef U_HIDE_DEPRECATED_API /** * The first unused time scale value. The limit of this enum * @deprecated ICU 59 The numeric value may change over time, see ICU ticket #12420. */ UDTS_MAX_SCALE #endif /* U_HIDE_DEPRECATED_API */ } 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 */ #ifndef U_HIDE_DEPRECATED_API /** * The number of time scale values, in other words limit of this enum. * * @see utmscale_getTimeScaleValue * @deprecated ICU 59 The numeric value may change over time, see ICU ticket #12420. */ UTSV_MAX_SCALE_VALUE=11 #endif /* U_HIDE_DEPRECATED_API */ } 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