utmscale.h File Reference

C API: Universal Time Scale. More...

#include "unicode/utypes.h"

Go to the source code of this file.

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_UNIX_MICROSECONDS_TIME, UDTS_MAX_SCALE
}
 

UDateTimeScale values are used to specify the time scale used for conversion into or out if the universal time scale.

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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.

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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.

Detailed Description

C API: Universal 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:

Table 1: Binary Time Scales

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

UDTS_UNIX_MICROSECONDS_TIME

int64_t

microseconds

Jan 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.

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.


Enumeration Type Documentation

UDateTimeScale values are used to specify the time scale used for conversion into or out if the universal time scale.

Stable:
ICU 3.2
Enumerator:
UDTS_JAVA_TIME 

Used in the JDK.

Data is a Java long (int64_t). Value is milliseconds since January 1, 1970.

Stable:
ICU 3.2
UDTS_UNIX_TIME 

Used on Unix systems.

Data is int32_t or int64_t. Value is seconds since January 1, 1970.

Stable:
ICU 3.2
UDTS_ICU4C_TIME 

Used in IUC4C.

Data is a double. Value is milliseconds since January 1, 1970.

Stable:
ICU 3.2
UDTS_WINDOWS_FILE_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_DOTNET_DATE_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_MAC_OLD_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_TIME 

Used in newer Macintosh systems.

Data is a double. Value is seconds since January 1, 2001.

Stable:
ICU 3.2
UDTS_EXCEL_TIME 

Used in Excel.

Data is an ?unknown?. Value is days since December 31, 1899.

Stable:
ICU 3.2
UDTS_DB2_TIME 

Used in DB2.

Data is an ?unknown?. Value is days since December 31, 1899.

Stable:
ICU 3.2
UDTS_UNIX_MICROSECONDS_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_MAX_SCALE 

The first unused time scale value.

The limit of this enum

Definition at line 202 of file utmscale.h.

UTimeScaleValue values are used to specify the time scale values to utmscale_getTimeScaleValue.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
Enumerator:
UTSV_UNITS_VALUE 

The constant used to select the units vale for a time scale.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
UTSV_EPOCH_OFFSET_VALUE 

The constant used to select the epoch offset value for a time scale.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
UTSV_FROM_MIN_VALUE 

The constant used to select the minimum from value for a time scale.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
UTSV_FROM_MAX_VALUE 

The constant used to select the maximum from value for a time scale.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
UTSV_TO_MIN_VALUE 

The constant used to select the minimum to value for a time scale.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
UTSV_TO_MAX_VALUE 

The constant used to select the maximum to value for a time scale.

See also:
utmscale_getTimeScaleValue
Stable:
ICU 3.2
UTSV_EPOCH_OFFSET_PLUS_1_VALUE 

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 also:
utmscale_getTimeScaleValue
Internal:
Do not use. This API is for internal use only. ICU 3.2
UTSV_EPOCH_OFFSET_MINUS_1_VALUE 

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 also:
utmscale_getTimeScaleValue
Internal:
Do not use. This API is for internal use only. ICU 3.2
UTSV_UNITS_ROUND_VALUE 

The constant used to select the units round value for a time scale.

NOTE: This is an internal value. DO NOT USE IT.

See also:
utmscale_getTimeScaleValue
Internal:
Do not use. This API is for internal use only. ICU 3.2
UTSV_MIN_ROUND_VALUE 

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 also:
utmscale_getTimeScaleValue
Internal:
Do not use. This API is for internal use only. ICU 3.2
UTSV_MAX_ROUND_VALUE 

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 also:
utmscale_getTimeScaleValue
Internal:
Do not use. This API is for internal use only. ICU 3.2
UTSV_MAX_SCALE_VALUE 

The number of time scale values, in other words limit of this enum.

See also:
utmscale_getTimeScaleValue

Definition at line 298 of file utmscale.h.


Function Documentation

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.

Parameters:
otherTime The int64_t datetime
timeScale The time scale to convert from
status The status code. Set to U_ILLEGAL_ARGUMENT_ERROR if the conversion is out of range.
Returns:
The datetime converted to the universal time scale
Stable:
ICU 3.2
int64_t utmscale_getTimeScaleValue ( UDateTimeScale  timeScale,
UTimeScaleValue  value,
UErrorCode status 
)

Get a value associated with a particular time scale.

Parameters:
timeScale The time scale
value A constant representing the value to get
status The status code. Set to U_ILLEGAL_ARGUMENT_ERROR if arguments are invalid.
Returns:
- the value.
Stable:
ICU 3.2
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.

Parameters:
universalTime The datetime in the universal time scale
timeScale The time scale to convert to
status The status code. Set to U_ILLEGAL_ARGUMENT_ERROR if the conversion is out of range.
Returns:
The datetime converted to the given time scale
Stable:
ICU 3.2
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