com.ibm.icu.util

Class UniversalTimeScale


public final class UniversalTimeScale
extends Object

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

SourceDatatypeUnitEpoch
JAVA_TIMElongmillisecondsJan 1, 1970
UNIX_TIMEint or longsecondsJan 1, 1970
ICU4CdoublemillisecondsJan 1, 1970
WINDOWS_FILE_TIMElongticks (100 nanoseconds)Jan 1, 1601
DOTNET_DATE_TIMElongticks (100 nanoseconds)Jan 1, 0001
MAC_OLD_TIMEintsecondsJan 1, 1904
MAC_TIMEdoublesecondsJan 1, 2001
EXCEL_TIME?daysDec 31, 1899
DB2_TIME?daysDec 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.

Unitslongdoubleint
1 sec5.84542×10¹¹285,420,920.94136.10
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

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.

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(BigDecimal otherTime, int timeScale)
Convert a BigDecimal datetime from the given time scale to the universal time scale.
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 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(BigDecimal universalTime, int timeScale)
Convert a datetime from the universal time scale to a BigDecimal in the given 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
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.

Field Details

DB2_TIME

public static final int DB2_TIME
Used in DB2. Data is a ?unknown?. Value is days since December 31, 1899.
Field Value:
8

DOTNET_DATE_TIME

public static final int DOTNET_DATE_TIME
Used in the .NET framework's System.DateTime structure. Data is a long. Value is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
Field Value:
4

EPOCH_OFFSET_MINUS_1_VALUE

public static final int EPOCH_OFFSET_MINUS_1_VALUE
The constant used to select the epoch offset minus 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 minus one.
Field Value:
7

EPOCH_OFFSET_PLUS_1_VALUE

public static final int 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.
Field Value:
6

EPOCH_OFFSET_VALUE

public static final int EPOCH_OFFSET_VALUE
The constant used to select the epoch offset value for a time scale.
Field Value:
1

EXCEL_TIME

public static final int EXCEL_TIME
Used in Excel. Data is a ?unknown?. Value is days since December 31, 1899.
Field Value:
7

FROM_MAX_VALUE

public static final int FROM_MAX_VALUE
The constant used to select the maximum from value for a time scale.
Field Value:
3

FROM_MIN_VALUE

public static final int FROM_MIN_VALUE
The constant used to select the minimum from value for a time scale.
Field Value:
2

ICU4C_TIME

public static final int ICU4C_TIME
Used in the ICU4C. Data is a double. Value is milliseconds since January 1, 1970.
Field Value:
2

JAVA_TIME

public static final int JAVA_TIME
Used in the JDK. Data is a long. Value is milliseconds since January 1, 1970.
Field Value:
0

MAC_OLD_TIME

public static final int MAC_OLD_TIME
Used in older Macintosh systems. Data is an int. Value is seconds since January 1, 1904.
Field Value:
5

MAC_TIME

public static final int MAC_TIME
Used in the JDK. Data is a double. Value is milliseconds since January 1, 2001.
Field Value:
6

MAX_ROUND_VALUE

public static final int 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.
Field Value:
10

MAX_SCALE

public static final int MAX_SCALE
This is the first unused time scale value.
Field Value:
9

MAX_SCALE_VALUE

public static final int MAX_SCALE_VALUE
The number of time scale values. NOTE: This is an internal value. DO NOT USE IT.
Field Value:
11

MIN_ROUND_VALUE

public static final int 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.
Field Value:
9

TO_MAX_VALUE

public static final int TO_MAX_VALUE
The constant used to select the maximum to value for a time scale.
Field Value:
5

TO_MIN_VALUE

public static final int TO_MIN_VALUE
The constant used to select the minimum to value for a time scale.
Field Value:
4

UNITS_ROUND_VALUE

public static final int 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.
Field Value:
8

UNITS_VALUE

public static final int UNITS_VALUE
The constant used to select the units value for a time scale.
Field Value:
0

UNIX_TIME

public static final int UNIX_TIME
Used in Unix systems. Data is an int or a long. Value is seconds since January 1, 1970.
Field Value:
1

WINDOWS_FILE_TIME

public static final int WINDOWS_FILE_TIME
Used in Windows for file times. Data is a long. Value is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
Field Value:
3

Method Details

bigDecimalFrom

public static BigDecimal bigDecimalFrom(BigDecimal otherTime,
                                        int timeScale)
Convert a 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

bigDecimalFrom

public static BigDecimal bigDecimalFrom(double otherTime,
                                        int timeScale)
Convert a 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

bigDecimalFrom

public static BigDecimal bigDecimalFrom(long otherTime,
                                        int timeScale)
Convert a 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

from

public static long from(long otherTime,
                        int timeScale)
Convert a 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

getTimeScaleValue

public static long getTimeScaleValue(int scale,
                                     int value)
Get a value associated with a particular time scale.
Parameters:
scale - - the time scale
value - - a constant representing the value to get
Returns:
- the value.

toBigDecimal

public static BigDecimal toBigDecimal(BigDecimal universalTime,
                                      int timeScale)
Convert a datetime from the universal time scale to a 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

toBigDecimal

public static BigDecimal toBigDecimal(long universalTime,
                                      int timeScale)
Convert a datetime from the universal time scale to a 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

toBigDecimalTrunc

public static BigDecimal toBigDecimalTrunc(BigDecimal universalTime,
                                           int timeScale)
Convert a time in the Universal Time Scale into another time scale. The division used to do the conversion rounds down. NOTE: This is an internal routine used by the tool that generates the to and from limits. Use it at your own risk.
Parameters:
universalTime - the time in the Universal Time scale
timeScale - the time scale to convert to
Returns:
the time in the given time scale

toLong

public 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. 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

Copyright (c) 2006 IBM Corporation and others.