482 lines
13 KiB
C
482 lines
13 KiB
C
/*
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*******************************************************************************
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* Copyright (C) 2004 - 2006, International Business Machines Corporation and
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* others. All Rights Reserved.
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*******************************************************************************
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*/
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#ifndef UTMSCALE_H
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#define UTMSCALE_H
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#include "unicode/utypes.h"
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#if !UCONFIG_NO_FORMATTING
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/**
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* \file
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* \brief C API: Universal Time Scale
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*
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* There are quite a few different conventions for binary datetime, depending on different
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* platforms and protocols. Some of these have severe drawbacks. For example, people using
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* Unix time (seconds since Jan 1, 1970) think that they are safe until near the year 2038.
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* But cases can and do arise where arithmetic manipulations causes serious problems. Consider
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* the computation of the average of two datetimes, for example: if one calculates them with
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* <code>averageTime = (time1 + time2)/2</code>, there will be overflow even with dates
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* around the present. Moreover, even if these problems don't occur, there is the issue of
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* conversion back and forth between different systems.
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*
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* <p>
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* Binary datetimes differ in a number of ways: the datatype, the unit,
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* and the epoch (origin). We'll refer to these as time scales. For example:
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*
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* <table border="1" cellspacing="0" cellpadding="4">
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* <caption>Table 1: Binary Time Scales</caption>
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* <tr>
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* <th align="left">Source</th>
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* <th align="left">Datatype</th>
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* <th align="left">Unit</th>
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* <th align="left">Epoch</th>
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* </tr>
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*
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* <tr>
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* <td>UDTS_JAVA_TIME</td>
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* <td>int64_t</td>
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* <td>milliseconds</td>
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* <td>Jan 1, 1970</td>
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* </tr>
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* <tr>
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*
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* <td>UDTS_UNIX_TIME</td>
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* <td>int32_t or int64_t</td>
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* <td>seconds</td>
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* <td>Jan 1, 1970</td>
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* </tr>
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* <tr>
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* <td>UDTS_ICU4C_TIME</td>
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*
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* <td>double</td>
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* <td>milliseconds</td>
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* <td>Jan 1, 1970</td>
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* </tr>
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* <tr>
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* <td>UDTS_WINDOWS_FILE_TIME</td>
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* <td>int64_t</td>
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*
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* <td>ticks (100 nanoseconds)</td>
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* <td>Jan 1, 1601</td>
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* </tr>
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* <tr>
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* <td>UDTS_DOTNET_DATE_TIME</td>
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* <td>int64_t</td>
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* <td>ticks (100 nanoseconds)</td>
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*
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* <td>Jan 1, 0001</td>
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* </tr>
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* <tr>
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* <td>UDTS_MAC_OLD_TIME</td>
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* <td>int32_t or int64_t</td>
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* <td>seconds</td>
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* <td>Jan 1, 1904</td>
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*
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* </tr>
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* <tr>
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* <td>UDTS_MAC_TIME</td>
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* <td>double</td>
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* <td>seconds</td>
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* <td>Jan 1, 2001</td>
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* </tr>
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*
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* <tr>
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* <td>UDTS_EXCEL_TIME</td>
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* <td>?</td>
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* <td>days</td>
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* <td>Dec 31, 1899</td>
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* </tr>
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* <tr>
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*
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* <td>UDTS_DB2_TIME</td>
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* <td>?</td>
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* <td>days</td>
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* <td>Dec 31, 1899</td>
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* </tr>
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*
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* <tr>
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* <td>UDTS_UNIX_MICROSECONDS_TIME</td>
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* <td>int64_t</td>
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* <td>microseconds</td>
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* <td>Jan 1, 1970</td>
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* </tr>
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* </table>
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*
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* <p>
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* All of the epochs start at 00:00 am (the earliest possible time on the day in question),
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* and are assumed to be UTC.
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*
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* <p>
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* The ranges for different datatypes are given in the following table (all values in years).
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* The range of years includes the entire range expressible with positive and negative
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* values of the datatype. The range of years for double is the range that would be allowed
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* without losing precision to the corresponding unit.
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*
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* <table border="1" cellspacing="0" cellpadding="4">
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* <tr>
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* <th align="left">Units</th>
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* <th align="left">int64_t</th>
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* <th align="left">double</th>
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* <th align="left">int32_t</th>
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* </tr>
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*
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* <tr>
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* <td>1 sec</td>
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* <td align="right">5.84542x10<sup>11</sup></td>
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* <td align="right">285,420,920.94</td>
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* <td align="right">136.10</td>
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* </tr>
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* <tr>
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*
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* <td>1 millisecond</td>
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* <td align="right">584,542,046.09</td>
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* <td align="right">285,420.92</td>
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* <td align="right">0.14</td>
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* </tr>
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* <tr>
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* <td>1 microsecond</td>
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*
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* <td align="right">584,542.05</td>
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* <td align="right">285.42</td>
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* <td align="right">0.00</td>
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* </tr>
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* <tr>
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* <td>100 nanoseconds (tick)</td>
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* <td align="right">58,454.20</td>
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* <td align="right">28.54</td>
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* <td align="right">0.00</td>
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* </tr>
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* <tr>
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* <td>1 nanosecond</td>
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* <td align="right">584.5420461</td>
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* <td align="right">0.2854</td>
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* <td align="right">0.00</td>
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* </tr>
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* </table>
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*
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* <p>
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* These functions implement a universal time scale which can be used as a 'pivot',
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* and provide conversion functions to and from all other major time scales.
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* This datetimes to be converted to the pivot time, safely manipulated,
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* and converted back to any other datetime time scale.
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*
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*<p>
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* So what to use for this pivot? Java time has plenty of range, but cannot represent
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* .NET <code>System.DateTime</code> values without severe loss of precision. ICU4C time addresses this by using a
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* <code>double</code> that is otherwise equivalent to the Java time. However, there are disadvantages
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* with <code>doubles</code>. They provide for much more graceful degradation in arithmetic operations.
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* But they only have 53 bits of accuracy, which means that they will lose precision when
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* converting back and forth to ticks. What would really be nice would be a
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* <code>long double</code> (80 bits -- 64 bit mantissa), but that is not supported on most systems.
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*
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*<p>
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* The Unix extended time uses a structure with two components: time in seconds and a
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* fractional field (microseconds). However, this is clumsy, slow, and
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* prone to error (you always have to keep track of overflow and underflow in the
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* fractional field). <code>BigDecimal</code> would allow for arbitrary precision and arbitrary range,
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* but we do not want to use this as the normal type, because it is slow and does not
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* have a fixed size.
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*
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*<p>
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* Because of these issues, we ended up concluding that the .NET framework's
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* <code>System.DateTime</code> would be the best pivot. However, we use the full range
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* allowed by the datatype, allowing for datetimes back to 29,000 BC and up to 29,000 AD.
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* This time scale is very fine grained, does not lose precision, and covers a range that
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* will meet almost all requirements. It will not handle the range that Java times do,
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* but frankly, being able to handle dates before 29,000 BC or after 29,000 AD is of very limited interest.
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*
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*/
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/**
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* <code>UDateTimeScale</code> values are used to specify the time scale used for
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* conversion into or out if the universal time scale.
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*
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* @stable ICU 3.2
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*/
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typedef enum UDateTimeScale {
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/**
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* Used in the JDK. Data is a Java <code>long</code> (<code>int64_t</code>). Value
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* is milliseconds since January 1, 1970.
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*
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* @stable ICU 3.2
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*/
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UDTS_JAVA_TIME = 0,
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/**
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* Used on Unix systems. Data is <code>int32_t</code> or <code>int64_t</code>. Value
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* is seconds since January 1, 1970.
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*
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* @stable ICU 3.2
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*/
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UDTS_UNIX_TIME,
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/**
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* Used in IUC4C. Data is a <code>double</code>. Value
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* is milliseconds since January 1, 1970.
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*
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* @stable ICU 3.2
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*/
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UDTS_ICU4C_TIME,
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/**
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* Used in Windows for file times. Data is an <code>int64_t</code>. Value
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* is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
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*
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* @stable ICU 3.2
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*/
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UDTS_WINDOWS_FILE_TIME,
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/**
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* Used in the .NET framework's <code>System.DateTime</code> structure. Data is an <code>int64_t</code>. Value
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* is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
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*
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* @stable ICU 3.2
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*/
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UDTS_DOTNET_DATE_TIME,
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/**
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* Used in older Macintosh systems. Data is <code>int32_t</code> or <code>int64_t</code>. Value
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* is seconds since January 1, 1904.
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*
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* @stable ICU 3.2
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*/
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UDTS_MAC_OLD_TIME,
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/**
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* Used in newer Macintosh systems. Data is a <code>double</code>. Value
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* is seconds since January 1, 2001.
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*
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* @stable ICU 3.2
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*/
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UDTS_MAC_TIME,
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/**
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* Used in Excel. Data is an <code>?unknown?</code>. Value
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* is days since December 31, 1899.
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*
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* @stable ICU 3.2
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*/
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UDTS_EXCEL_TIME,
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/**
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* Used in DB2. Data is an <code>?unknown?</code>. Value
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* is days since December 31, 1899.
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*
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* @stable ICU 3.2
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*/
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UDTS_DB2_TIME,
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/**
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* Data is a <code>long</code>. Value is microseconds since January 1, 1970.
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* Similar to Unix time (linear value from 1970) and struct timeval
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* (microseconds resolution).
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*
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* @draft ICU 3.8
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*/
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UDTS_UNIX_MICROSECONDS_TIME,
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/**
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* The first unused time scale value. The limit of this enum
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*/
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UDTS_MAX_SCALE
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} UDateTimeScale;
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/**
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* <code>UTimeScaleValue</code> values are used to specify the time scale values
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* to <code>utmscale_getTimeScaleValue</code>.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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typedef enum UTimeScaleValue {
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/**
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* The constant used to select the units vale
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* for a time scale.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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UTSV_UNITS_VALUE = 0,
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/**
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* The constant used to select the epoch offset value
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* for a time scale.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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UTSV_EPOCH_OFFSET_VALUE=1,
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/**
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* The constant used to select the minimum from value
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* for a time scale.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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UTSV_FROM_MIN_VALUE=2,
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/**
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* The constant used to select the maximum from value
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* for a time scale.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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UTSV_FROM_MAX_VALUE=3,
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/**
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* The constant used to select the minimum to value
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* for a time scale.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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UTSV_TO_MIN_VALUE=4,
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/**
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* The constant used to select the maximum to value
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* for a time scale.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @stable ICU 3.2
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*/
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UTSV_TO_MAX_VALUE=5,
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#ifndef U_HIDE_INTERNAL_API
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/**
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* The constant used to select the epoch plus one value
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* for a time scale.
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*
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* NOTE: This is an internal value. DO NOT USE IT. May not
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* actually be equal to the epoch offset value plus one.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @internal ICU 3.2
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*/
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UTSV_EPOCH_OFFSET_PLUS_1_VALUE=6,
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/**
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* The constant used to select the epoch plus one value
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* for a time scale.
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*
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* NOTE: This is an internal value. DO NOT USE IT. May not
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* actually be equal to the epoch offset value plus one.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @internal ICU 3.2
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*/
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UTSV_EPOCH_OFFSET_MINUS_1_VALUE=7,
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/**
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* The constant used to select the units round value
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* for a time scale.
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*
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* NOTE: This is an internal value. DO NOT USE IT.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @internal ICU 3.2
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*/
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UTSV_UNITS_ROUND_VALUE=8,
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/**
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* The constant used to select the minimum safe rounding value
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* for a time scale.
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*
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* NOTE: This is an internal value. DO NOT USE IT.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @internal ICU 3.2
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*/
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UTSV_MIN_ROUND_VALUE=9,
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/**
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* The constant used to select the maximum safe rounding value
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* for a time scale.
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*
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* NOTE: This is an internal value. DO NOT USE IT.
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*
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* @see utmscale_getTimeScaleValue
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*
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* @internal ICU 3.2
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*/
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UTSV_MAX_ROUND_VALUE=10,
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#endif /* U_HIDE_INTERNAL_API */
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/**
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* The number of time scale values, in other words limit of this enum.
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*
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* @see utmscale_getTimeScaleValue
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*/
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UTSV_MAX_SCALE_VALUE=11
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} UTimeScaleValue;
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/**
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* Get a value associated with a particular time scale.
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*
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* @param timeScale The time scale
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* @param value A constant representing the value to get
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* @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if arguments are invalid.
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* @return - the value.
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*
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* @stable ICU 3.2
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*/
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U_STABLE int64_t U_EXPORT2
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utmscale_getTimeScaleValue(UDateTimeScale timeScale, UTimeScaleValue value, UErrorCode *status);
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/* Conversion to 'universal time scale' */
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/**
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* Convert a <code>int64_t</code> datetime from the given time scale to the universal time scale.
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*
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* @param otherTime The <code>int64_t</code> datetime
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* @param timeScale The time scale to convert from
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* @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if the conversion is out of range.
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*
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* @return The datetime converted to the universal time scale
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*
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* @stable ICU 3.2
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*/
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U_STABLE int64_t U_EXPORT2
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utmscale_fromInt64(int64_t otherTime, UDateTimeScale timeScale, UErrorCode *status);
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/* Conversion from 'universal time scale' */
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/**
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* Convert a datetime from the universal time scale to a <code>int64_t</code> in the given time scale.
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*
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* @param universalTime The datetime in the universal time scale
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* @param timeScale The time scale to convert to
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* @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if the conversion is out of range.
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*
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* @return The datetime converted to the given time scale
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*
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* @stable ICU 3.2
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*/
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U_STABLE int64_t U_EXPORT2
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utmscale_toInt64(int64_t universalTime, UDateTimeScale timeScale, UErrorCode *status);
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#endif /* #if !UCONFIG_NO_FORMATTING */
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#endif
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