icuSources/i18n/unicode/utmscale.h

   1 /*
   2 *******************************************************************************
   3 * Copyright (C) 2004, International Business Machines Corporation and
   4 * others. All Rights Reserved.
   5 *******************************************************************************
   6 */
   7
   8 #ifndef UTMSCALE_H
   9 #define UTMSCALE_H
  10
  11 #include "unicode/utypes.h"
  12
  13 #if !UCONFIG_NO_FORMATTING
  14
  15 /**
  16  * \file
  17  * \brief C API: Universal Time Scale
  18  *
  19  * There are quite a few different conventions for binary datetime, depending on different
  20  * platforms and protocols. Some of these have severe drawbacks. For example, people using
  21  * Unix time (seconds since Jan 1, 1970) think that they are safe until near the year 2038.
  22  * But cases can and do arise where arithmetic manipulations causes serious problems. Consider
  23  * the computation of the average of two datetimes, for example: if one calculates them with
  24  * <code>averageTime = (time1 + time2)/2</code>, there will be overflow even with dates
  25  * around the present. Moreover, even if these problems don't occur, there is the issue of
  26  * conversion back and forth between different systems.
  27  *
  28  * <p>
  29  * Binary datetimes differ in a number of ways: the datatype, the unit,
  30  * and the epoch (origin). We'll refer to these as time scales. For example:
  31  *
  32  * <table border="1" cellspacing="0" cellpadding="4">
  33  *  <caption>Table 1: Binary Time Scales</caption>
  34  *  <tr>
  35  *    <th align="left">Source</th>
  36  *    <th align="left">Datatype</th>
  37  *    <th align="left">Unit</th>
  38  *    <th align="left">Epoch</th>
  39  *  </tr>
  40  *
  41  *  <tr>
  42  *    <td>JAVA_TIME</td>
  43  *    <td>int64_t</td>
  44  *    <td>milliseconds</td>
  45  *    <td>Jan 1, 1970</td>
  46  *  </tr>
  47  *  <tr>
  48  *
  49  *    <td>UNIX_TIME</td>
  50  *    <td>int32_t or int64_t</td>
  51  *    <td>seconds</td>
  52  *    <td>Jan 1, 1970</td>
  53  *  </tr>
  54  *  <tr>
  55  *    <td>ICU4C_TIME</td>
  56  *
  57  *    <td>double</td>
  58  *    <td>milliseconds</td>
  59  *    <td>Jan 1, 1970</td>
  60  *  </tr>
  61  *  <tr>
  62  *    <td>WINDOWS_FILE_TIME</td>
  63  *    <td>int64_t</td>
  64  *
  65  *    <td>ticks (100 nanoseconds)</td>
  66  *    <td>Jan 1, 1601</td>
  67  *  </tr>
  68  *  <tr>
  69  *    <td>WINDOWS_DATE_TIME</td>
  70  *    <td>int64_t</td>
  71  *    <td>ticks (100 nanoseconds)</td>
  72  *
  73  *    <td>Jan 1, 0001</td>
  74  *  </tr>
  75  *  <tr>
  76  *    <td>MAC_OLD_TIME</td>
  77  *    <td>int32_t</td>
  78  *    <td>seconds</td>
  79  *    <td>Jan 1, 1904</td>
  80  *
  81  *  </tr>
  82  *  <tr>
  83  *    <td>MAC_TIME</td>
  84  *    <td>double</td>
  85  *    <td>seconds</td>
  86  *    <td>Jan 1, 2001</td>
  87  *  </tr>
  88  *
  89  *  <tr>
  90  *    <td>EXCEL_TIME</td>
  91  *    <td>?</td>
  92  *    <td>days</td>
  93  *    <td>Dec 31, 1899</td>
  94  *  </tr>
  95  *  <tr>
  96  *
  97  *    <td>DB2_TIME</td>
  98  *    <td>?</td>
  99  *    <td>days</td>
 100  *    <td>Dec 31, 1899</td>
 101  *  </tr>
 102  * </table>
 103  *
 104  * <p>
 105  * All of the epochs start at 00:00 am (the earliest possible time on the day in question),
 106  * and are assumed to be UTC.
 107  *
 108  * <p>
 109  * The ranges for different datatypes are given in the following table (all values in years).
 110  * The range of years includes the entire range expressible with positive and negative
 111  * values of the datatype. The range of years for double is the range that would be allowed
 112  * without losing precision to the corresponding unit.
 113  *
 114  * <table border="1" cellspacing="0" cellpadding="4">
 115  *  <tr>
 116  *    <th align="left">Units</th>
 117  *    <th align="left">int64_t</th>
 118  *    <th align="left">double</th>
 119  *    <th align="left">int32_t</th>
 120  *  </tr>
 121  *
 122  *  <tr>
 123  *    <td>1 sec</td>
 124  *    <td align="right">5.84542x10<sup>11</sup></td>
 125  *    <td align="right">285,420,920.94</td>
 126  *    <td align="right">136.10</td>
 127  *  </tr>
 128  *  <tr>
 129  *
 130  *    <td>1 millisecond</td>
 131  *    <td align="right">584,542,046.09</td>
 132  *    <td align="right">285,420.92</td>
 133  *    <td align="right">0.14</td>
 134  *  </tr>
 135  *  <tr>
 136  *    <td>1 microsecond</td>
 137  *
 138  *    <td align="right">584,542.05</td>
 139  *    <td align="right">285.42</td>
 140  *    <td align="right">0.00</td>
 141  *  </tr>
 142  *  <tr>
 143  *    <td>100 nanoseconds (tick)</td>
 144  *    <td align="right">58,454.20</td>
 145  *    <td align="right">28.54</td>
 146  *    <td align="right">0.00</td>
 147  *  </tr>
 148  *  <tr>
 149  *    <td>1 nanosecond</td>
 150  *    <td align="right">584.5420461</td>
 151  *    <td align="right">0.2854</td>
 152  *    <td align="right">0.00</td>
 153  *  </tr>
 154  * </table>
 155  *
 156  * <p>
 157  * These functions implement a universal time scale which can be used as a 'pivot',
 158  * and provide conversion functions to and from all other major time scales.
 159  * This datetimes to be converted to the pivot time, safely manipulated,
 160  * and converted back to any other datetime time scale.
 161  *
 162  *<p>
 163  * So what to use for this pivot? Java time has plenty of range, but cannot represent
 164  * Windows datetimes without severe loss of precision. ICU4C time addresses this by using a
 165  * <code>double</code> that is otherwise equivalent to the Java time. However, there are disadvantages
 166  * with <code>doubles</code>. They provide for much more graceful degradation in arithmetic operations.
 167  * But they only have 53 bits of accuracy, which means that they will lose precision when
 168  * converting back and forth to ticks. What would really be nice would be a
 169  * long double (80 bits -- 64 bit mantissa), but that is not supported on most systems.
 170  *
 171  *<p>
 172  * The Unix extended time uses a structure with two components: time in seconds and a
 173  * fractional field (microseconds). However, this is clumsy, slow, and
 174  * prone to error (you always have to keep track of overflow and underflow in the
 175  * fractional field). <code>BigDecimal</code> would allow for arbitrary precision and arbitrary range,
 176  * but we do not want to use this as the normal type, because it is slow and does not
 177  * have a fixed size.
 178  *
 179  *<p>
 180  * Because of these issues, we ended up concluding that the Windows datetime would be the
 181  * best pivot. However, we use the full range allowed by the datatype, allowing for
 182  * datetimes back to 29,000 BC and up to 29,000 AD. This time scale is very fine grained,
 183  * does not lose precision, and covers a range that will meet almost all requirements.
 184  * It will not handle the range that Java times do, but frankly, being able to handle dates
 185  * before 29,000 BC or after 29,000 AD is of very limited interest.
 186  *
 187  */
 188
 189 /**
 190  * <code>UDateTimeScale</code> values are used to specify the time scale used for
 191  * conversion into or out if the universal time scale.
 192  *
 193  * @draft ICU 3.2
 194  */
 195 typedef enum UDateTimeScale {
 196     /**
 197      * Used in the JDK. Data is a Java <code>long</code> (<code>int64_t</code>). Value
 198      * is milliseconds since January 1, 1970.
 199      *
 200      * @draft ICU 3.2
 201      */
 202     UDTS_JAVA_TIME = 0,
 203
 204     /**
 205      * Used on Unix systems. Data is <code>int32_t</code> or <code>int64_t</code>. Value
 206      * is seconds since January 1, 1970.
 207      *
 208      * @draft ICU 3.2
 209      */
 210     UDTS_UNIX_TIME,
 211
 212     /**
 213      * Used in IUC4C. Data is a <code>double</code>. Value
 214      * is milliseconds since January 1, 1970.
 215      *
 216      * @draft ICU 3.2
 217      */
 218     UDTS_ICU4C_TIME,
 219
 220     /**
 221      * Used in Windows for file times. Data is an <code>int64_t</code>. Value
 222      * is ticks (1 tick == 100 nanoseconds) since January 1, 1601.
 223      *
 224      * @draft ICU 3.2
 225      */
 226     UDTS_WINDOWS_FILE_TIME,
 227
 228     /**
 229      * Used in Windows for dates and times (?). Data is an <code>int64_t</code>. Value
 230      * is ticks (1 tick == 100 nanoseconds) since January 1, 0001.
 231      *
 232      * @draft ICU 3.2
 233      */
 234     UDTS_WINDOWS_DATE_TIME,
 235
 236     /**
 237      * Used in older Macintosh systems. Data is an <code>int32_t</code>. Value
 238      * is seconds since January 1, 1904.
 239      *
 240      * @draft ICU 3.2
 241      */
 242     UDTS_MAC_OLD_TIME,
 243
 244     /**
 245      * Used in newer Macintosh systems. Data is a <code>double</code>. Value
 246      * is seconds since January 1, 2001.
 247      *
 248      * @draft ICU 3.2
 249      */
 250     UDTS_MAC_TIME,
 251
 252     /**
 253      * Used in Excel. Data is an <code>?unknown?</code>. Value
 254      * is days since December 31, 1899.
 255      *
 256      * @draft ICU 3.2
 257      */
 258     UDTS_EXCEL_TIME,
 259
 260     /**
 261      * Used in DB2. Data is an <code>?unknown?</code>. Value
 262      * is days since December 31, 1899.
 263      *
 264      * @draft ICU 3.2
 265      */
 266     UDTS_DB2_TIME,
 267
 268     /**
 269      * The first unused time scale value.
 270      *
 271      * @draft ICU 3.2
 272      */
 273     UDTS_MAX_SCALE
 274 } UDateTimeScale;
 275
 276 typedef enum UTimeScaleValue {
 277     /**
 278      * The constant used to select the units vale
 279      * for a time scale.
 280      *
 281      * @see utms_getTimeScaleValue
 282      *
 283      * @draft ICU 3.2
 284      */
 285     UTSV_UNITS_VALUE = 0,
 286
 287     /**
 288      * The constant used to select the epoch offset value
 289      * for a time scale.
 290      *
 291      * @see utms_getTimeScaleValue
 292      *
 293      * @draft ICU 3.2
 294      */
 295     UTSV_EPOCH_OFFSET_VALUE,
 296
 297     /**
 298      * The constant used to select the minimum from value
 299      * for a time scale.
 300      *
 301      * @see utms_getTimeScaleValue
 302      *
 303      * @draft ICU 3.2
 304      */
 305     UTSV_FROM_MIN_VALUE,
 306
 307     /**
 308      * The constant used to select the maximum from value
 309      * for a time scale.
 310      *
 311      * @see utms_getTimeScaleValue
 312      *
 313      * @draft ICU 3.2
 314      */
 315     UTSV_FROM_MAX_VALUE,
 316
 317     /**
 318      * The constant used to select the minimum to value
 319      * for a time scale.
 320      *
 321      * @see utms_getTimeScaleValue
 322      *
 323      * @draft ICU 3.2
 324      */
 325     UTSV_TO_MIN_VALUE,
 326
 327     /**
 328      * The constant used to select the maximum to value
 329      * for a time scale.
 330      *
 331      * @see utms_getTimeScaleValue
 332      *
 333      * @draft ICU 3.2
 334      */
 335     UTSV_TO_MAX_VALUE,
 336
 337     /**
 338      * The constant used to select the epoch plus one value
 339      * for a time scale.
 340      *
 341      * NOTE: This is an internal value. DO NOT USE IT. May not
 342      * actually be equal to the epoch offset value plus one.
 343      *
 344      * @see utms_getTimeScaleValue
 345      *
 346      * @draft ICU 3.2
 347      */
 348     UTSV_EPOCH_OFFSET_PLUS_1_VALUE,
 349
 350     /**
 351      * The constant used to select the epoch plus one value
 352      * for a time scale.
 353      *
 354      * NOTE: This is an internal value. DO NOT USE IT. May not
 355      * actually be equal to the epoch offset value plus one.
 356      *
 357      * @see utms_getTimeScaleValue
 358      *
 359      * @draft ICU 3.2
 360      */
 361     UTSV_EPOCH_OFFSET_MINUS_1_VALUE,
 362
 363     /**
 364      * The constant used to select the units round value
 365      * for a time scale.
 366      *
 367      * NOTE: This is an internal value. DO NOT USE IT.
 368      *
 369      * @see utms_getTimeScaleValue
 370      *
 371      * @internal
 372      */
 373     UTSV_UNITS_ROUND_VALUE,
 374
 375     /**
 376      * The constant used to select the minimum safe rounding value
 377      * for a time scale.
 378      *
 379      * NOTE: This is an internal value. DO NOT USE IT.
 380      *
 381      * @see utms_getTimeScaleValue
 382      *
 383      * @internal
 384      */
 385     UTSV_MIN_ROUND_VALUE,
 386
 387     /**
 388      * The constant used to select the maximum safe rounding value
 389      * for a time scale.
 390      *
 391      * NOTE: This is an internal value. DO NOT USE IT.
 392      *
 393      * @see utms_getTimeScaleValue
 394      *
 395      * @internal
 396      */
 397     UTSV_MAX_ROUND_VALUE,
 398
 399     /**
 400      * The number of time scale values.
 401      *
 402      * NOTE: This is an internal value. DO NOT USE IT.
 403      *
 404      * @see utms_getTimeScaleValue
 405      *
 406      * @internal
 407      */
 408     UTSV_MAX_SCALE_VALUE
 409 } UTimeScaleValue;
 410
 411 /**
 412  * Get a value associated with a particular time scale.
 413  *
 414  * @param timeScale The time scale
 415  * @param value A constant representing the value to get
 416  * @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if arguments are invalid.
 417  * @return - the value.
 418  *
 419  * @draft ICU 3.2
 420  */
 421 U_DRAFT int64_t U_EXPORT2
 422     utmscale_getTimeScaleValue(UDateTimeScale timeScale, UTimeScaleValue value, UErrorCode *status);
 423
 424 /* Conversion to 'universal time scale' */
 425
 426 /**
 427  * Convert a <code>int64_t</code> datetime from the given time scale to the universal time scale.
 428  *
 429  * @param otherTime The <code>int64_t</code> datetime
 430  * @param timeScale The time scale to convert from
 431  * @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if the conversion is out of range.
 432  *
 433  * @return The datetime converted to the universal time scale
 434  *
 435  * @draft ICU 3.2
 436  */
 437 U_DRAFT int64_t U_EXPORT2
 438     utmscale_fromInt64(int64_t otherTime, UDateTimeScale timeScale, UErrorCode *status);
 439
 440 /* Conversion from 'universal time scale' */
 441
 442 /**
 443  * Convert a datetime from the universal time scale to a <code>int64_t</code> in the given time scale.
 444  *
 445  * @param universalTime The datetime in the universal time scale
 446  * @param timeScale The time scale to convert to
 447  * @param status The status code. Set to <code>U_ILLEGAL_ARGUMENT_ERROR</code> if the conversion is out of range.
 448  *
 449  * @return The datetime converted to the given time scale
 450  *
 451  * @draft ICU 3.2
 452  */
 453 U_DRAFT int64_t U_EXPORT2
 454     utmscale_toInt64(int64_t universalTime, UDateTimeScale timeScale, UErrorCode *status);
 455
 456 #endif /* #if !UCONFIG_NO_FORMATTING */
 457
 458 #endif
 459