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 // © 2016 and later: Unicode, Inc. and others.
 // License & terms of use: http://www.unicode.org/copyright.html
 /*
 *******************************************************************************
 * Copyright (C) 2004 - 2008, International Business Machines Corporation and
 * others. All Rights Reserved.
 *******************************************************************************
 */
 
 #ifndef UTMSCALE_H
 #define UTMSCALE_H
 
 #include "unicode/utypes.h"
 
 #if !UCONFIG_NO_FORMATTING
 
 /** 
  * \file
  * \brief 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
  * <code>averageTime = (time1 + time2)/2</code>, 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.
  *
  * <p>
  * 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 border="1" cellspacing="0" cellpadding="4">
  *  <caption>Table 1: Binary Time Scales</caption>
  *  <tr>
  *    <th align="left">Source</th>
  *    <th align="left">Datatype</th>
  *    <th align="left">Unit</th>
  *    <th align="left">Epoch</th>
  *  </tr>
  *
  *  <tr>
  *    <td>UDTS_JAVA_TIME</td>
  *    <td>int64_t</td>
  *    <td>milliseconds</td>
  *    <td>Jan 1, 1970</td>
  *  </tr>
  *  <tr>
  *
  *    <td>UDTS_UNIX_TIME</td>
  *    <td>int32_t or int64_t</td>
  *    <td>seconds</td>
  *    <td>Jan 1, 1970</td>
  *  </tr>
  *  <tr>
  *    <td>UDTS_ICU4C_TIME</td>
  *
  *    <td>double</td>
  *    <td>milliseconds</td>
  *    <td>Jan 1, 1970</td>
  *  </tr>
  *  <tr>
  *    <td>UDTS_WINDOWS_FILE_TIME</td>
  *    <td>int64_t</td>
  *
  *    <td>ticks (100 nanoseconds)</td>
  *    <td>Jan 1, 1601</td>
  *  </tr>
  *  <tr>
  *    <td>UDTS_DOTNET_DATE_TIME</td>
  *    <td>int64_t</td>
  *    <td>ticks (100 nanoseconds)</td>
  *
  *    <td>Jan 1, 0001</td>
  *  </tr>
  *  <tr>
  *    <td>UDTS_MAC_OLD_TIME</td>
  *    <td>int32_t or int64_t</td>
  *    <td>seconds</td>
  *    <td>Jan 1, 1904</td>
  *
  *  </tr>
  *  <tr>
  *    <td>UDTS_MAC_TIME</td>
  *    <td>double</td>
  *    <td>seconds</td>
  *    <td>Jan 1, 2001</td>
  *  </tr>
  *
  *  <tr>
  *    <td>UDTS_EXCEL_TIME</td>
  *    <td>?</td>
  *    <td>days</td>
  *    <td>Dec 31, 1899</td>
  *  </tr>
  *  <tr>
  *
  *    <td>UDTS_DB2_TIME</td>
  *    <td>?</td>
  *    <td>days</td>
  *    <td>Dec 31, 1899</td>
  *  </tr>
  *
  *  <tr>
  *    <td>UDTS_UNIX_MICROSECONDS_TIME</td>
  *    <td>int64_t</td>
  *    <td>microseconds</td>
  *    <td>Jan 1, 1970</td>
  *  </tr>
  * </table>
  *
  * <p>
  * All of the epochs start at 00:00 am (the earliest possible time on the day in question),
  * and are assumed to be UTC.
  *
  * <p>
  * 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.
  *
  * <table border="1" cellspacing="0" cellpadding="4">
  *  <tr>
  *    <th align="left">Units</th>
  *    <th align="left">int64_t</th>
  *    <th align="left">double</th>
  *    <th align="left">int32_t</th>
  *  </tr>
  *
  *  <tr>
  *    <td>1 sec</td>
  *    <td align="right">5.84542x10<sup>11</sup></td>
  *    <td align="right">285,420,920.94</td>
  *    <td align="right">136.10</td>
  *  </tr>
  *  <tr>
  *
  *    <td>1 millisecond</td>
  *    <td align="right">584,542,046.09</td>
  *    <td align="right">285,420.92</td>
  *    <td align="right">0.14</td>
  *  </tr>
  *  <tr>
  *    <td>1 microsecond</td>
  *
  *    <td align="right">584,542.05</td>
  *    <td align="right">285.42</td>
  *    <td align="right">0.00</td>
  *  </tr>
  *  <tr>
  *    <td>100 nanoseconds (tick)</td>
  *    <td align="right">58,454.20</td>
  *    <td align="right">28.54</td>
  *    <td align="right">0.00</td>
  *  </tr>
  *  <tr>
  *    <td>1 nanosecond</td>
  *    <td align="right">584.5420461</td>
  *    <td align="right">0.2854</td>
  *    <td align="right">0.00</td>
  *  </tr>
  * </table>
  *
  * <p>
  * 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.
  *
  *<p>
  * So what to use for this pivot? Java time has plenty of range, but cannot represent
  * .NET <code>System.DateTime</code> values without severe loss of precision. ICU4C time addresses this by using a
  * <code>double</code> that is otherwise equivalent to the Java time. However, there are disadvantages
  * with <code>doubles</code>. 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
  * <code>long double</code> (80 bits -- 64 bit mantissa), but that is not supported on most systems.
  *
  *<p>
  * 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). <code>BigDecimal</code> 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.
  *
  *<p>
  * Because of these issues, we ended up concluding that the .NET framework's
  * <code>System.DateTime</code> 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.
  *
  */
 
 /**
  * <code>UDateTimeScale</code> 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 <code>long</code> (<code>int64_t</code>). Value
      * is milliseconds since January 1, 1970.
      *
      * @stable ICU 3.2
      */
     UDTS_JAVA_TIME = 0,
 
     /**
      * Used on Unix systems. Data is <code>int32_t</code> or <code>int64_t</code>. Value
      * is seconds since January 1, 1970.
      *
      * @stable ICU 3.2
      */
     UDTS_UNIX_TIME,
     
     /**
      * Used in IUC4C. Data is a <code>double</code>. Value
      * is milliseconds since January 1, 1970.
      *
      * @stable ICU 3.2
      */
     UDTS_ICU4C_TIME,
     
     /**
      * Used in Windows for file times. Data is an <code>int64_t</code>. 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 <code>System.DateTime</code> structure. Data is an <code>int64_t</code>. 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 <code>int32_t</code> or <code>int64_t</code>. Value
      * is seconds since January 1, 1904.
      *
      * @stable ICU 3.2
      */
     UDTS_MAC_OLD_TIME,
     
     /**
      * Used in newer Macintosh systems. Data is a <code>double</code>. Value
      * is seconds since January 1, 2001.
      *
      * @stable ICU 3.2
      */
     UDTS_MAC_TIME,
     
     /**
      * Used in Excel. Data is an <code>?unknown?</code>. Value
      * is days since December 31, 1899.
      *
      * @stable ICU 3.2
      */
     UDTS_EXCEL_TIME,
     
     /**
      * Used in DB2. Data is an <code>?unknown?</code>. Value
      * is days since December 31, 1899.
      *
      * @stable ICU 3.2
      */
     UDTS_DB2_TIME,
 
     /**
      * Data is a <code>long</code>. 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;
 
 /**
  * <code>UTimeScaleValue</code> values are used to specify the time scale values
  * to <code>utmscale_getTimeScaleValue</code>.
  *
  * @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 <code>U_ILLEGAL_ARGUMENT_ERROR</code> if arguments are invalid.
  * @return - the value.
  * 
  * @stable ICU 3.2
  */
 U_CAPI int64_t U_EXPORT2
     utmscale_getTimeScaleValue(UDateTimeScale timeScale, UTimeScaleValue value, UErrorCode *status);
 
 /* Conversion to 'universal time scale' */
 
 /**
  * Convert a <code>int64_t</code> datetime from the given time scale to the universal time scale.
  *
  * @param otherTime The <code>int64_t</code> datetime
  * @param timeScale The time scale to convert from
  * @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if the conversion is out of range.
  * 
  * @return The datetime converted to the universal time scale
  *
  * @stable ICU 3.2
  */
 U_CAPI 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 <code>int64_t</code> 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 <code>U_ILLEGAL_ARGUMENT_ERROR</code> if the conversion is out of range.
  * 
  * @return The datetime converted to the given time scale
  *
  * @stable ICU 3.2
  */
 U_CAPI int64_t U_EXPORT2
     utmscale_toInt64(int64_t universalTime, UDateTimeScale timeScale, UErrorCode *status);
 
 #endif /* #if !UCONFIG_NO_FORMATTING */
 
 #endif
 

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