text: // © 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
  