lib/libc/stdtime/strftime.c

   1 /*
   2  * Copyright (c) 1989 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Copyright (c) 2011 The FreeBSD Foundation
   6  * All rights reserved.
   7  * Portions of this software were developed by David Chisnall
   8  * under sponsorship from the FreeBSD Foundation.
   9  *
  10  * Redistribution and use in source and binary forms are permitted
  11  * provided that the above copyright notice and this paragraph are
  12  * duplicated in all such forms and that any documentation,
  13  * advertising materials, and other materials related to such
  14  * distribution and use acknowledge that the software was developed
  15  * by the University of California, Berkeley. The name of the
  16  * University may not be used to endorse or promote products derived
  17  * from this software without specific prior written permission.
  18  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  19  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  20  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  21  *
  22  * @(#)strftime.c       5.4 (Berkeley) 3/14/89
  23  * $FreeBSD: head/lib/libc/stdtime/strftime.c 237211 2012-06-17 21:40:13Z jilles $
  24  */
  25
  26
  27 #include "namespace.h"
  28 #include "private.h"
  29
  30 #include "tzfile.h"
  31 #include <fcntl.h>
  32 #include <sys/stat.h>
  33 #include "un-namespace.h"
  34 #include "timelocal.h"
  35
  36 static char *   _add(const char *, char *, const char *);
  37 static char *   _conv(int, const char *, char *, const char *);
  38 static char *   _fmt(const char *, const struct tm *, char *, const char *,
  39                         int *, locale_t);
  40 static char *   _yconv(int, int, int, int, char *, const char *);
  41
  42 extern char *   tzname[];
  43
  44 #ifndef YEAR_2000_NAME
  45 #define YEAR_2000_NAME  "CHECK_STRFTIME_FORMATS_FOR_TWO_DIGIT_YEARS"
  46 #endif /* !defined YEAR_2000_NAME */
  47
  48 #define IN_NONE 0
  49 #define IN_SOME 1
  50 #define IN_THIS 2
  51 #define IN_ALL  3
  52
  53 #define PAD_DEFAULT     0
  54 #define PAD_LESS        1
  55 #define PAD_SPACE       2
  56 #define PAD_ZERO        3
  57
  58 static const char fmt_padding[][4][5] = {
  59         /* DEFAULT,     LESS,   SPACE,  ZERO */
  60 #define PAD_FMT_MONTHDAY        0
  61 #define PAD_FMT_HMS             0
  62 #define PAD_FMT_CENTURY         0
  63 #define PAD_FMT_SHORTYEAR       0
  64 #define PAD_FMT_MONTH           0
  65 #define PAD_FMT_WEEKOFYEAR      0
  66 #define PAD_FMT_DAYOFMONTH      0
  67         { "%02d",       "%d",   "%2d",  "%02d" },
  68 #define PAD_FMT_SDAYOFMONTH     1
  69 #define PAD_FMT_SHMS            1
  70         { "%2d",        "%d",   "%2d",  "%02d" },
  71 #define PAD_FMT_DAYOFYEAR       2
  72         { "%03d",       "%d",   "%3d",  "%03d" },
  73 #define PAD_FMT_YEAR            3
  74         { "%04d",       "%d",   "%4d",  "%04d" }
  75 };
  76
  77 size_t
  78 strftime_l(char * __restrict s, size_t maxsize, const char * __restrict format,
  79     const struct tm * __restrict t, locale_t loc)
  80 {
  81         char *  p;
  82         int     warn;
  83         FIX_LOCALE(loc);
  84
  85         tzset();
  86         warn = IN_NONE;
  87         p = _fmt(((format == NULL) ? "%c" : format), t, s, s + maxsize, &warn, loc);
  88 #ifndef NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU
  89         if (warn != IN_NONE && getenv(YEAR_2000_NAME) != NULL) {
  90                 (void) fprintf_l(stderr, loc, "\n");
  91                 if (format == NULL)
  92                         (void) fprintf_l(stderr, loc, "NULL strftime format ");
  93                 else    (void) fprintf_l(stderr, loc, "strftime format \"%s\" ",
  94                                 format);
  95                 (void) fprintf_l(stderr, loc, "yields only two digits of years in ");
  96                 if (warn == IN_SOME)
  97                         (void) fprintf_l(stderr, loc, "some locales");
  98                 else if (warn == IN_THIS)
  99                         (void) fprintf_l(stderr, loc, "the current locale");
 100                 else    (void) fprintf_l(stderr, loc, "all locales");
 101                 (void) fprintf_l(stderr, loc, "\n");
 102         }
 103 #endif /* !defined NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU */
 104         if (p == s + maxsize)
 105                 return 0;
 106         *p = '\0';
 107         return p - s;
 108 }
 109
 110 size_t
 111 strftime(char * __restrict s, size_t maxsize, const char * __restrict format,
 112     const struct tm * __restrict t)
 113 {
 114         return strftime_l(s, maxsize, format, t, __get_locale());
 115 }
 116
 117 static char *
 118 _fmt(format, t, pt, ptlim, warnp, loc)
 119 const char *            format;
 120 const struct tm * const t;
 121 char *                  pt;
 122 const char * const      ptlim;
 123 int *                   warnp;
 124 locale_t        loc;
 125 {
 126         int Ealternative, Oalternative, PadIndex;
 127         struct lc_time_T *tptr = __get_current_time_locale(loc);
 128
 129         for ( ; *format; ++format) {
 130                 if (*format == '%') {
 131                         Ealternative = 0;
 132                         Oalternative = 0;
 133                         PadIndex         = PAD_DEFAULT;
 134 label:
 135                         switch (*++format) {
 136                         case '\0':
 137                                 --format;
 138                                 break;
 139                         case 'A':
 140                                 pt = _add((t->tm_wday < 0 ||
 141                                         t->tm_wday >= DAYSPERWEEK) ?
 142                                         "?" : tptr->weekday[t->tm_wday],
 143                                         pt, ptlim);
 144                                 continue;
 145                         case 'a':
 146                                 pt = _add((t->tm_wday < 0 ||
 147                                         t->tm_wday >= DAYSPERWEEK) ?
 148                                         "?" : tptr->wday[t->tm_wday],
 149                                         pt, ptlim);
 150                                 continue;
 151                         case 'B':
 152                                 pt = _add((t->tm_mon < 0 ||
 153                                         t->tm_mon >= MONSPERYEAR) ?
 154                                         "?" : (Oalternative ? tptr->alt_month :
 155                                         tptr->month)[t->tm_mon],
 156                                         pt, ptlim);
 157                                 continue;
 158                         case 'b':
 159                         case 'h':
 160                                 pt = _add((t->tm_mon < 0 ||
 161                                         t->tm_mon >= MONSPERYEAR) ?
 162                                         "?" : tptr->mon[t->tm_mon],
 163                                         pt, ptlim);
 164                                 continue;
 165                         case 'C':
 166                                 /*
 167                                 ** %C used to do a...
 168                                 **      _fmt("%a %b %e %X %Y", t);
 169                                 ** ...whereas now POSIX 1003.2 calls for
 170                                 ** something completely different.
 171                                 ** (ado, 1993-05-24)
 172                                 */
 173                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 0,
 174                                         pt, ptlim);
 175                                 continue;
 176                         case 'c':
 177                                 {
 178                                 int warn2 = IN_SOME;
 179
 180                                 pt = _fmt(tptr->c_fmt, t, pt, ptlim, &warn2, loc);
 181                                 if (warn2 == IN_ALL)
 182                                         warn2 = IN_THIS;
 183                                 if (warn2 > *warnp)
 184                                         *warnp = warn2;
 185                                 }
 186                                 continue;
 187                         case 'D':
 188                                 pt = _fmt("%m/%d/%y", t, pt, ptlim, warnp, loc);
 189                                 continue;
 190                         case 'd':
 191                                 pt = _conv(t->tm_mday, fmt_padding[PAD_FMT_DAYOFMONTH][PadIndex],
 192                                         pt, ptlim);
 193                                 continue;
 194                         case 'E':
 195                                 if (Ealternative || Oalternative)
 196                                         break;
 197                                 Ealternative++;
 198                                 goto label;
 199                         case 'O':
 200                                 /*
 201                                 ** C99 locale modifiers.
 202                                 ** The sequences
 203                                 **      %Ec %EC %Ex %EX %Ey %EY
 204                                 **      %Od %oe %OH %OI %Om %OM
 205                                 **      %OS %Ou %OU %OV %Ow %OW %Oy
 206                                 ** are supposed to provide alternate
 207                                 ** representations.
 208                                 **
 209                                 ** FreeBSD extension
 210                                 **      %OB
 211                                 */
 212                                 if (Ealternative || Oalternative)
 213                                         break;
 214                                 Oalternative++;
 215                                 goto label;
 216                         case 'e':
 217                                 pt = _conv(t->tm_mday,
 218                                         fmt_padding[PAD_FMT_SDAYOFMONTH][PadIndex], pt, ptlim);
 219                                 continue;
 220                         case 'F':
 221                                 pt = _fmt("%Y-%m-%d", t, pt, ptlim, warnp, loc);
 222                                 continue;
 223                         case 'H':
 224                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_HMS][PadIndex],
 225                                         pt, ptlim);
 226                                 continue;
 227                         case 'I':
 228                                 pt = _conv((t->tm_hour % 12) ?
 229                                         (t->tm_hour % 12) : 12,
 230                                         fmt_padding[PAD_FMT_HMS][PadIndex], pt, ptlim);
 231                                 continue;
 232                         case 'j':
 233                                 pt = _conv(t->tm_yday + 1,
 234                                         fmt_padding[PAD_FMT_DAYOFYEAR][PadIndex], pt, ptlim);
 235                                 continue;
 236                         case 'k':
 237                                 /*
 238                                 ** This used to be...
 239                                 **      _conv(t->tm_hour % 12 ?
 240                                 **              t->tm_hour % 12 : 12, 2, ' ');
 241                                 ** ...and has been changed to the below to
 242                                 ** match SunOS 4.1.1 and Arnold Robbins'
 243                                 ** strftime version 3.0. That is, "%k" and
 244                                 ** "%l" have been swapped.
 245                                 ** (ado, 1993-05-24)
 246                                 */
 247                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_SHMS][PadIndex],
 248                                         pt, ptlim);
 249                                 continue;
 250 #ifdef KITCHEN_SINK
 251                         case 'K':
 252                                 /*
 253                                 ** After all this time, still unclaimed!
 254                                 */
 255                                 pt = _add("kitchen sink", pt, ptlim);
 256                                 continue;
 257 #endif /* defined KITCHEN_SINK */
 258                         case 'l':
 259                                 /*
 260                                 ** This used to be...
 261                                 **      _conv(t->tm_hour, 2, ' ');
 262                                 ** ...and has been changed to the below to
 263                                 ** match SunOS 4.1.1 and Arnold Robbin's
 264                                 ** strftime version 3.0. That is, "%k" and
 265                                 ** "%l" have been swapped.
 266                                 ** (ado, 1993-05-24)
 267                                 */
 268                                 pt = _conv((t->tm_hour % 12) ?
 269                                         (t->tm_hour % 12) : 12,
 270                                         fmt_padding[PAD_FMT_SHMS][PadIndex], pt, ptlim);
 271                                 continue;
 272                         case 'M':
 273                                 pt = _conv(t->tm_min, fmt_padding[PAD_FMT_HMS][PadIndex],
 274                                         pt, ptlim);
 275                                 continue;
 276                         case 'm':
 277                                 pt = _conv(t->tm_mon + 1,
 278                                         fmt_padding[PAD_FMT_MONTH][PadIndex], pt, ptlim);
 279                                 continue;
 280                         case 'n':
 281                                 pt = _add("\n", pt, ptlim);
 282                                 continue;
 283                         case 'p':
 284                                 pt = _add((t->tm_hour >= (HOURSPERDAY / 2)) ?
 285                                         tptr->pm :
 286                                         tptr->am,
 287                                         pt, ptlim);
 288                                 continue;
 289                         case 'R':
 290                                 pt = _fmt("%H:%M", t, pt, ptlim, warnp, loc);
 291                                 continue;
 292                         case 'r':
 293                                 pt = _fmt(tptr->ampm_fmt, t, pt, ptlim,
 294                                         warnp, loc);
 295                                 continue;
 296                         case 'S':
 297                                 pt = _conv(t->tm_sec, fmt_padding[PAD_FMT_HMS][PadIndex],
 298                                         pt, ptlim);
 299                                 continue;
 300                         case 's':
 301                                 {
 302                                         struct tm       tm;
 303                                         char            buf[INT_STRLEN_MAXIMUM(
 304                                                                 time_t) + 1];
 305                                         time_t          mkt;
 306
 307                                         tm = *t;
 308                                         mkt = mktime(&tm);
 309                                         if (TYPE_SIGNED(time_t))
 310                                                 (void) sprintf(buf, "%ld",
 311                                                         (long) mkt);
 312                                         else    (void) sprintf(buf, "%lu",
 313                                                         (unsigned long) mkt);
 314                                         pt = _add(buf, pt, ptlim);
 315                                 }
 316                                 continue;
 317                         case 'T':
 318                                 pt = _fmt("%H:%M:%S", t, pt, ptlim, warnp, loc);
 319                                 continue;
 320                         case 't':
 321                                 pt = _add("\t", pt, ptlim);
 322                                 continue;
 323                         case 'U':
 324                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 325                                         t->tm_wday) / DAYSPERWEEK,
 326                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex], pt, ptlim);
 327                                 continue;
 328                         case 'u':
 329                                 /*
 330                                 ** From Arnold Robbins' strftime version 3.0:
 331                                 ** "ISO 8601: Weekday as a decimal number
 332                                 ** [1 (Monday) - 7]"
 333                                 ** (ado, 1993-05-24)
 334                                 */
 335                                 pt = _conv((t->tm_wday == 0) ?
 336                                         DAYSPERWEEK : t->tm_wday,
 337                                         "%d", pt, ptlim);
 338                                 continue;
 339                         case 'V':       /* ISO 8601 week number */
 340                         case 'G':       /* ISO 8601 year (four digits) */
 341                         case 'g':       /* ISO 8601 year (two digits) */
 342 /*
 343 ** From Arnold Robbins' strftime version 3.0: "the week number of the
 344 ** year (the first Monday as the first day of week 1) as a decimal number
 345 ** (01-53)."
 346 ** (ado, 1993-05-24)
 347 **
 348 ** From "http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html" by Markus Kuhn:
 349 ** "Week 01 of a year is per definition the first week which has the
 350 ** Thursday in this year, which is equivalent to the week which contains
 351 ** the fourth day of January. In other words, the first week of a new year
 352 ** is the week which has the majority of its days in the new year. Week 01
 353 ** might also contain days from the previous year and the week before week
 354 ** 01 of a year is the last week (52 or 53) of the previous year even if
 355 ** it contains days from the new year. A week starts with Monday (day 1)
 356 ** and ends with Sunday (day 7). For example, the first week of the year
 357 ** 1997 lasts from 1996-12-30 to 1997-01-05..."
 358 ** (ado, 1996-01-02)
 359 */
 360                                 {
 361                                         int     year;
 362                                         int     base;
 363                                         int     yday;
 364                                         int     wday;
 365                                         int     w;
 366
 367                                         year = t->tm_year;
 368                                         base = TM_YEAR_BASE;
 369                                         yday = t->tm_yday;
 370                                         wday = t->tm_wday;
 371                                         for ( ; ; ) {
 372                                                 int     len;
 373                                                 int     bot;
 374                                                 int     top;
 375
 376                                                 len = isleap_sum(year, base) ?
 377                                                         DAYSPERLYEAR :
 378                                                         DAYSPERNYEAR;
 379                                                 /*
 380                                                 ** What yday (-3 ... 3) does
 381                                                 ** the ISO year begin on?
 382                                                 */
 383                                                 bot = ((yday + 11 - wday) %
 384                                                         DAYSPERWEEK) - 3;
 385                                                 /*
 386                                                 ** What yday does the NEXT
 387                                                 ** ISO year begin on?
 388                                                 */
 389                                                 top = bot -
 390                                                         (len % DAYSPERWEEK);
 391                                                 if (top < -3)
 392                                                         top += DAYSPERWEEK;
 393                                                 top += len;
 394                                                 if (yday >= top) {
 395                                                         ++base;
 396                                                         w = 1;
 397                                                         break;
 398                                                 }
 399                                                 if (yday >= bot) {
 400                                                         w = 1 + ((yday - bot) /
 401                                                                 DAYSPERWEEK);
 402                                                         break;
 403                                                 }
 404                                                 --base;
 405                                                 yday += isleap_sum(year, base) ?
 406                                                         DAYSPERLYEAR :
 407                                                         DAYSPERNYEAR;
 408                                         }
 409 #ifdef XPG4_1994_04_09
 410                                         if ((w == 52 &&
 411                                                 t->tm_mon == TM_JANUARY) ||
 412                                                 (w == 1 &&
 413                                                 t->tm_mon == TM_DECEMBER))
 414                                                         w = 53;
 415 #endif /* defined XPG4_1994_04_09 */
 416                                         if (*format == 'V')
 417                                                 pt = _conv(w, fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 418                                                         pt, ptlim);
 419                                         else if (*format == 'g') {
 420                                                 *warnp = IN_ALL;
 421                                                 pt = _yconv(year, base, 0, 1,
 422                                                         pt, ptlim);
 423                                         } else  pt = _yconv(year, base, 1, 1,
 424                                                         pt, ptlim);
 425                                 }
 426                                 continue;
 427                         case 'v':
 428                                 /*
 429                                 ** From Arnold Robbins' strftime version 3.0:
 430                                 ** "date as dd-bbb-YYYY"
 431                                 ** (ado, 1993-05-24)
 432                                 */
 433                                 pt = _fmt("%e-%b-%Y", t, pt, ptlim, warnp, loc);
 434                                 continue;
 435                         case 'W':
 436                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 437                                         (t->tm_wday ?
 438                                         (t->tm_wday - 1) :
 439                                         (DAYSPERWEEK - 1))) / DAYSPERWEEK,
 440                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex], pt, ptlim);
 441                                 continue;
 442                         case 'w':
 443                                 pt = _conv(t->tm_wday, "%d", pt, ptlim);
 444                                 continue;
 445                         case 'X':
 446                                 pt = _fmt(tptr->X_fmt, t, pt, ptlim, warnp, loc);
 447                                 continue;
 448                         case 'x':
 449                                 {
 450                                 int     warn2 = IN_SOME;
 451
 452                                 pt = _fmt(tptr->x_fmt, t, pt, ptlim, &warn2, loc);
 453                                 if (warn2 == IN_ALL)
 454                                         warn2 = IN_THIS;
 455                                 if (warn2 > *warnp)
 456                                         *warnp = warn2;
 457                                 }
 458                                 continue;
 459                         case 'y':
 460                                 *warnp = IN_ALL;
 461                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 0, 1,
 462                                         pt, ptlim);
 463                                 continue;
 464                         case 'Y':
 465                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 1,
 466                                         pt, ptlim);
 467                                 continue;
 468                         case 'Z':
 469 #ifdef TM_ZONE
 470                                 if (t->TM_ZONE != NULL)
 471                                         pt = _add(t->TM_ZONE, pt, ptlim);
 472                                 else
 473 #endif /* defined TM_ZONE */
 474                                 if (t->tm_isdst >= 0)
 475                                         pt = _add(tzname[t->tm_isdst != 0],
 476                                                 pt, ptlim);
 477                                 /*
 478                                 ** C99 says that %Z must be replaced by the
 479                                 ** empty string if the time zone is not
 480                                 ** determinable.
 481                                 */
 482                                 continue;
 483                         case 'z':
 484                                 {
 485                                 int             diff;
 486                                 char const *    sign;
 487
 488                                 if (t->tm_isdst < 0)
 489                                         continue;
 490 #ifdef TM_GMTOFF
 491                                 diff = t->TM_GMTOFF;
 492 #else /* !defined TM_GMTOFF */
 493                                 /*
 494                                 ** C99 says that the UTC offset must
 495                                 ** be computed by looking only at
 496                                 ** tm_isdst. This requirement is
 497                                 ** incorrect, since it means the code
 498                                 ** must rely on magic (in this case
 499                                 ** altzone and timezone), and the
 500                                 ** magic might not have the correct
 501                                 ** offset. Doing things correctly is
 502                                 ** tricky and requires disobeying C99;
 503                                 ** see GNU C strftime for details.
 504                                 ** For now, punt and conform to the
 505                                 ** standard, even though it's incorrect.
 506                                 **
 507                                 ** C99 says that %z must be replaced by the
 508                                 ** empty string if the time zone is not
 509                                 ** determinable, so output nothing if the
 510                                 ** appropriate variables are not available.
 511                                 */
 512                                 if (t->tm_isdst == 0)
 513                                         diff = -timezone;
 514                                 else
 515 #ifdef ALTZONE
 516                                         diff = -altzone;
 517 #else /* !defined ALTZONE */
 518                                         continue;
 519 #endif /* !defined ALTZONE */
 520 #endif /* !defined TM_GMTOFF */
 521                                 if (diff < 0) {
 522                                         sign = "-";
 523                                         diff = -diff;
 524                                 } else  sign = "+";
 525                                 pt = _add(sign, pt, ptlim);
 526                                 diff /= SECSPERMIN;
 527                                 diff = (diff / MINSPERHOUR) * 100 +
 528                                         (diff % MINSPERHOUR);
 529                                 pt = _conv(diff,
 530                                         fmt_padding[PAD_FMT_YEAR][PadIndex], pt, ptlim);
 531                                 }
 532                                 continue;
 533                         case '+':
 534                                 pt = _fmt(tptr->date_fmt, t, pt, ptlim,
 535                                         warnp, loc);
 536                                 continue;
 537                         case '-':
 538                                 if (PadIndex != PAD_DEFAULT)
 539                                         break;
 540                                 PadIndex = PAD_LESS;
 541                                 goto label;
 542                         case '_':
 543                                 if (PadIndex != PAD_DEFAULT)
 544                                         break;
 545                                 PadIndex = PAD_SPACE;
 546                                 goto label;
 547                         case '0':
 548                                 if (PadIndex != PAD_DEFAULT)
 549                                         break;
 550                                 PadIndex = PAD_ZERO;
 551                                 goto label;
 552                         case '%':
 553                         /*
 554                         ** X311J/88-090 (4.12.3.5): if conversion char is
 555                         ** undefined, behavior is undefined. Print out the
 556                         ** character itself as printf(3) also does.
 557                         */
 558                         default:
 559                                 break;
 560                         }
 561                 }
 562                 if (pt == ptlim)
 563                         break;
 564                 *pt++ = *format;
 565         }
 566         return pt;
 567 }
 568
 569 static char *
 570 _conv(n, format, pt, ptlim)
 571 const int               n;
 572 const char * const      format;
 573 char * const            pt;
 574 const char * const      ptlim;
 575 {
 576         char    buf[INT_STRLEN_MAXIMUM(int) + 1];
 577
 578         (void) sprintf(buf, format, n);
 579         return _add(buf, pt, ptlim);
 580 }
 581
 582 static char *
 583 _add(str, pt, ptlim)
 584 const char *            str;
 585 char *                  pt;
 586 const char * const      ptlim;
 587 {
 588         while (pt < ptlim && (*pt = *str++) != '\0')
 589                 ++pt;
 590         return pt;
 591 }
 592
 593 /*
 594 ** POSIX and the C Standard are unclear or inconsistent about
 595 ** what %C and %y do if the year is negative or exceeds 9999.
 596 ** Use the convention that %C concatenated with %y yields the
 597 ** same output as %Y, and that %Y contains at least 4 bytes,
 598 ** with more only if necessary.
 599 */
 600
 601 static char *
 602 _yconv(a, b, convert_top, convert_yy, pt, ptlim)
 603 const int               a;
 604 const int               b;
 605 const int               convert_top;
 606 const int               convert_yy;
 607 char *                  pt;
 608 const char * const      ptlim;
 609 {
 610         register int    lead;
 611         register int    trail;
 612
 613 #define DIVISOR 100
 614         trail = a % DIVISOR + b % DIVISOR;
 615         lead = a / DIVISOR + b / DIVISOR + trail / DIVISOR;
 616         trail %= DIVISOR;
 617         if (trail < 0 && lead > 0) {
 618                 trail += DIVISOR;
 619                 --lead;
 620         } else if (lead < 0 && trail > 0) {
 621                 trail -= DIVISOR;
 622                 ++lead;
 623         }
 624         if (convert_top) {
 625                 if (lead == 0 && trail < 0)
 626                         pt = _add("-0", pt, ptlim);
 627                 else    pt = _conv(lead, "%02d", pt, ptlim);
 628         }
 629         if (convert_yy)
 630                 pt = _conv(((trail < 0) ? -trail : trail), "%02d", pt, ptlim);
 631         return pt;
 632 }