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
  23 #ifndef lint
  24 #ifndef NOID
  25 static const char       elsieid[] = "@(#)strftime.3     8.3";
  26 /*
  27  * Based on the UCB version with the ID appearing below.
  28  * This is ANSIish only when "multibyte character == plain character".
  29  */
  30 #endif /* !defined NOID */
  31 #endif /* !defined lint */
  32
  33 #include "namespace.h"
  34 #include "private.h"
  35
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 static const char       sccsid[] = "@(#)strftime.c      5.4 (Berkeley) 3/14/89";
  38 #endif /* LIBC_SCCS and not lint */
  39 #include <sys/cdefs.h>
  40 __FBSDID("$FreeBSD$");
  41
  42 #include "tzfile.h"
  43 #include <fcntl.h>
  44 #include <sys/stat.h>
  45 #include "un-namespace.h"
  46 #include "timelocal.h"
  47
  48 static char *   _add(const char *, char *, const char *);
  49 static char *   _conv(int, const char *, char *, const char *, locale_t);
  50 static char *   _fmt(const char *, const struct tm *, char *, const char *,
  51                         int *, locale_t);
  52 static char *   _yconv(int, int, int, int, char *, const char *, locale_t);
  53
  54 extern char *   tzname[];
  55
  56 #ifndef YEAR_2000_NAME
  57 #define YEAR_2000_NAME  "CHECK_STRFTIME_FORMATS_FOR_TWO_DIGIT_YEARS"
  58 #endif /* !defined YEAR_2000_NAME */
  59
  60 #define IN_NONE 0
  61 #define IN_SOME 1
  62 #define IN_THIS 2
  63 #define IN_ALL  3
  64
  65 #define PAD_DEFAULT     0
  66 #define PAD_LESS        1
  67 #define PAD_SPACE       2
  68 #define PAD_ZERO        3
  69
  70 static const char fmt_padding[][4][5] = {
  71         /* DEFAULT,     LESS,   SPACE,  ZERO */
  72 #define PAD_FMT_MONTHDAY        0
  73 #define PAD_FMT_HMS             0
  74 #define PAD_FMT_CENTURY         0
  75 #define PAD_FMT_SHORTYEAR       0
  76 #define PAD_FMT_MONTH           0
  77 #define PAD_FMT_WEEKOFYEAR      0
  78 #define PAD_FMT_DAYOFMONTH      0
  79         { "%02d",       "%d",   "%2d",  "%02d" },
  80 #define PAD_FMT_SDAYOFMONTH     1
  81 #define PAD_FMT_SHMS            1
  82         { "%2d",        "%d",   "%2d",  "%02d" },
  83 #define PAD_FMT_DAYOFYEAR       2
  84         { "%03d",       "%d",   "%3d",  "%03d" },
  85 #define PAD_FMT_YEAR            3
  86         { "%04d",       "%d",   "%4d",  "%04d" }
  87 };
  88
  89 size_t
  90 strftime_l(char * __restrict s, size_t maxsize, const char * __restrict format,
  91     const struct tm * __restrict t, locale_t loc)
  92 {
  93         char *  p;
  94         int     warn;
  95         FIX_LOCALE(loc);
  96
  97         tzset();
  98         warn = IN_NONE;
  99         p = _fmt(((format == NULL) ? "%c" : format), t, s, s + maxsize, &warn, loc);
 100 #ifndef NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU
 101         if (warn != IN_NONE && getenv(YEAR_2000_NAME) != NULL) {
 102                 (void) fprintf_l(stderr, loc, "\n");
 103                 if (format == NULL)
 104                         (void) fputs("NULL strftime format ", stderr);
 105                 else    (void) fprintf_l(stderr, loc, "strftime format \"%s\" ",
 106                                 format);
 107                 (void) fputs("yields only two digits of years in ", stderr);
 108                 if (warn == IN_SOME)
 109                         (void) fputs("some locales", stderr);
 110                 else if (warn == IN_THIS)
 111                         (void) fputs("the current locale", stderr);
 112                 else    (void) fputs("all locales", stderr);
 113                 (void) fputs("\n", stderr);
 114         }
 115 #endif /* !defined NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU */
 116         if (p == s + maxsize)
 117                 return (0);
 118         *p = '\0';
 119         return p - s;
 120 }
 121
 122 size_t
 123 strftime(char * __restrict s, size_t maxsize, const char * __restrict format,
 124     const struct tm * __restrict t)
 125 {
 126         return strftime_l(s, maxsize, format, t, __get_locale());
 127 }
 128
 129 static char *
 130 _fmt(const char *format, const struct tm * const t, char *pt,
 131     const char * const ptlim, int *warnp, locale_t loc)
 132 {
 133         int Ealternative, Oalternative, PadIndex;
 134         struct lc_time_T *tptr = __get_current_time_locale(loc);
 135
 136         for ( ; *format; ++format) {
 137                 if (*format == '%') {
 138                         Ealternative = 0;
 139                         Oalternative = 0;
 140                         PadIndex         = PAD_DEFAULT;
 141 label:
 142                         switch (*++format) {
 143                         case '\0':
 144                                 --format;
 145                                 break;
 146                         case 'A':
 147                                 pt = _add((t->tm_wday < 0 ||
 148                                         t->tm_wday >= DAYSPERWEEK) ?
 149                                         "?" : tptr->weekday[t->tm_wday],
 150                                         pt, ptlim);
 151                                 continue;
 152                         case 'a':
 153                                 pt = _add((t->tm_wday < 0 ||
 154                                         t->tm_wday >= DAYSPERWEEK) ?
 155                                         "?" : tptr->wday[t->tm_wday],
 156                                         pt, ptlim);
 157                                 continue;
 158                         case 'B':
 159                                 pt = _add((t->tm_mon < 0 ||
 160                                         t->tm_mon >= MONSPERYEAR) ?
 161                                         "?" : (Oalternative ? tptr->alt_month :
 162                                         tptr->month)[t->tm_mon],
 163                                         pt, ptlim);
 164                                 continue;
 165                         case 'b':
 166                         case 'h':
 167                                 pt = _add((t->tm_mon < 0 ||
 168                                         t->tm_mon >= MONSPERYEAR) ?
 169                                         "?" : tptr->mon[t->tm_mon],
 170                                         pt, ptlim);
 171                                 continue;
 172                         case 'C':
 173                                 /*
 174                                  * %C used to do a...
 175                                  *      _fmt("%a %b %e %X %Y", t);
 176                                  * ...whereas now POSIX 1003.2 calls for
 177                                  * something completely different.
 178                                  * (ado, 1993-05-24)
 179                                  */
 180                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 0,
 181                                         pt, ptlim, loc);
 182                                 continue;
 183                         case 'c':
 184                                 {
 185                                 int warn2 = IN_SOME;
 186
 187                                 pt = _fmt(tptr->c_fmt, t, pt, ptlim, &warn2, loc);
 188                                 if (warn2 == IN_ALL)
 189                                         warn2 = IN_THIS;
 190                                 if (warn2 > *warnp)
 191                                         *warnp = warn2;
 192                                 }
 193                                 continue;
 194                         case 'D':
 195                                 pt = _fmt("%m/%d/%y", t, pt, ptlim, warnp, loc);
 196                                 continue;
 197                         case 'd':
 198                                 pt = _conv(t->tm_mday,
 199                                         fmt_padding[PAD_FMT_DAYOFMONTH][PadIndex],
 200                                         pt, ptlim, loc);
 201                                 continue;
 202                         case 'E':
 203                                 if (Ealternative || Oalternative)
 204                                         break;
 205                                 Ealternative++;
 206                                 goto label;
 207                         case 'O':
 208                                 /*
 209                                  * C99 locale modifiers.
 210                                  * The sequences
 211                                  *      %Ec %EC %Ex %EX %Ey %EY
 212                                  *      %Od %oe %OH %OI %Om %OM
 213                                  *      %OS %Ou %OU %OV %Ow %OW %Oy
 214                                  * are supposed to provide alternate
 215                                  * representations.
 216                                  *
 217                                  * FreeBSD extension
 218                                  *      %OB
 219                                  */
 220                                 if (Ealternative || Oalternative)
 221                                         break;
 222                                 Oalternative++;
 223                                 goto label;
 224                         case 'e':
 225                                 pt = _conv(t->tm_mday,
 226                                         fmt_padding[PAD_FMT_SDAYOFMONTH][PadIndex],
 227                                         pt, ptlim, loc);
 228                                 continue;
 229                         case 'F':
 230                                 pt = _fmt("%Y-%m-%d", t, pt, ptlim, warnp, loc);
 231                                 continue;
 232                         case 'H':
 233                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_HMS][PadIndex],
 234                                         pt, ptlim, loc);
 235                                 continue;
 236                         case 'I':
 237                                 pt = _conv((t->tm_hour % 12) ?
 238                                         (t->tm_hour % 12) : 12,
 239                                         fmt_padding[PAD_FMT_HMS][PadIndex],
 240                                         pt, ptlim, loc);
 241                                 continue;
 242                         case 'j':
 243                                 pt = _conv(t->tm_yday + 1,
 244                                         fmt_padding[PAD_FMT_DAYOFYEAR][PadIndex],
 245                                         pt, ptlim, loc);
 246                                 continue;
 247                         case 'k':
 248                                 /*
 249                                  * This used to be...
 250                                  *      _conv(t->tm_hour % 12 ?
 251                                  *              t->tm_hour % 12 : 12, 2, ' ');
 252                                  * ...and has been changed to the below to
 253                                  * match SunOS 4.1.1 and Arnold Robbins'
 254                                  * strftime version 3.0. That is, "%k" and
 255                                  * "%l" have been swapped.
 256                                  * (ado, 1993-05-24)
 257                                  */
 258                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_SHMS][PadIndex],
 259                                         pt, ptlim, loc);
 260                                 continue;
 261 #ifdef KITCHEN_SINK
 262                         case 'K':
 263                                 /*
 264                                 ** After all this time, still unclaimed!
 265                                 */
 266                                 pt = _add("kitchen sink", pt, ptlim);
 267                                 continue;
 268 #endif /* defined KITCHEN_SINK */
 269                         case 'l':
 270                                 /*
 271                                  * This used to be...
 272                                  *      _conv(t->tm_hour, 2, ' ');
 273                                  * ...and has been changed to the below to
 274                                  * match SunOS 4.1.1 and Arnold Robbin's
 275                                  * strftime version 3.0. That is, "%k" and
 276                                  * "%l" have been swapped.
 277                                  * (ado, 1993-05-24)
 278                                  */
 279                                 pt = _conv((t->tm_hour % 12) ?
 280                                         (t->tm_hour % 12) : 12,
 281                                         fmt_padding[PAD_FMT_SHMS][PadIndex],
 282                                         pt, ptlim, loc);
 283                                 continue;
 284                         case 'M':
 285                                 pt = _conv(t->tm_min, fmt_padding[PAD_FMT_HMS][PadIndex],
 286                                         pt, ptlim, loc);
 287                                 continue;
 288                         case 'm':
 289                                 pt = _conv(t->tm_mon + 1,
 290                                         fmt_padding[PAD_FMT_MONTH][PadIndex],
 291                                         pt, ptlim, loc);
 292                                 continue;
 293                         case 'n':
 294                                 pt = _add("\n", pt, ptlim);
 295                                 continue;
 296                         case 'p':
 297                                 pt = _add((t->tm_hour >= (HOURSPERDAY / 2)) ?
 298                                         tptr->pm : tptr->am,
 299                                         pt, ptlim);
 300                                 continue;
 301                         case 'R':
 302                                 pt = _fmt("%H:%M", t, pt, ptlim, warnp, loc);
 303                                 continue;
 304                         case 'r':
 305                                 pt = _fmt(tptr->ampm_fmt, t, pt, ptlim,
 306                                         warnp, loc);
 307                                 continue;
 308                         case 'S':
 309                                 pt = _conv(t->tm_sec, fmt_padding[PAD_FMT_HMS][PadIndex],
 310                                         pt, ptlim, loc);
 311                                 continue;
 312                         case 's':
 313                                 {
 314                                         struct tm       tm;
 315                                         char            buf[INT_STRLEN_MAXIMUM(
 316                                                                 time_t) + 1];
 317                                         time_t          mkt;
 318
 319                                         tm = *t;
 320                                         mkt = mktime(&tm);
 321                                         if (TYPE_SIGNED(time_t))
 322                                                 (void) sprintf_l(buf, loc, "%ld",
 323                                                         (long) mkt);
 324                                         else    (void) sprintf_l(buf, loc, "%lu",
 325                                                         (unsigned long) mkt);
 326                                         pt = _add(buf, pt, ptlim);
 327                                 }
 328                                 continue;
 329                         case 'T':
 330                                 pt = _fmt("%H:%M:%S", t, pt, ptlim, warnp, loc);
 331                                 continue;
 332                         case 't':
 333                                 pt = _add("\t", pt, ptlim);
 334                                 continue;
 335                         case 'U':
 336                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 337                                         t->tm_wday) / DAYSPERWEEK,
 338                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 339                                         pt, ptlim, loc);
 340                                 continue;
 341                         case 'u':
 342                                 /*
 343                                  * From Arnold Robbins' strftime version 3.0:
 344                                  * "ISO 8601: Weekday as a decimal number
 345                                  * [1 (Monday) - 7]"
 346                                  * (ado, 1993-05-24)
 347                                  */
 348                                 pt = _conv((t->tm_wday == 0) ?
 349                                         DAYSPERWEEK : t->tm_wday,
 350                                         "%d", pt, ptlim, loc);
 351                                 continue;
 352                         case 'V':       /* ISO 8601 week number */
 353                         case 'G':       /* ISO 8601 year (four digits) */
 354                         case 'g':       /* ISO 8601 year (two digits) */
 355 /*
 356  * From Arnold Robbins' strftime version 3.0: "the week number of the
 357  * year (the first Monday as the first day of week 1) as a decimal number
 358  * (01-53)."
 359  * (ado, 1993-05-24)
 360  *
 361  * From "http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html" by Markus Kuhn:
 362  * "Week 01 of a year is per definition the first week which has the
 363  * Thursday in this year, which is equivalent to the week which contains
 364  * the fourth day of January. In other words, the first week of a new year
 365  * is the week which has the majority of its days in the new year. Week 01
 366  * might also contain days from the previous year and the week before week
 367  * 01 of a year is the last week (52 or 53) of the previous year even if
 368  * it contains days from the new year. A week starts with Monday (day 1)
 369  * and ends with Sunday (day 7). For example, the first week of the year
 370  * 1997 lasts from 1996-12-30 to 1997-01-05..."
 371  * (ado, 1996-01-02)
 372  */
 373                                 {
 374                                         int     year;
 375                                         int     base;
 376                                         int     yday;
 377                                         int     wday;
 378                                         int     w;
 379
 380                                         year = t->tm_year;
 381                                         base = TM_YEAR_BASE;
 382                                         yday = t->tm_yday;
 383                                         wday = t->tm_wday;
 384                                         for ( ; ; ) {
 385                                                 int     len;
 386                                                 int     bot;
 387                                                 int     top;
 388
 389                                                 len = isleap_sum(year, base) ?
 390                                                         DAYSPERLYEAR :
 391                                                         DAYSPERNYEAR;
 392                                                 /*
 393                                                  * What yday (-3 ... 3) does
 394                                                  * the ISO year begin on?
 395                                                  */
 396                                                 bot = ((yday + 11 - wday) %
 397                                                         DAYSPERWEEK) - 3;
 398                                                 /*
 399                                                  * What yday does the NEXT
 400                                                  * ISO year begin on?
 401                                                  */
 402                                                 top = bot -
 403                                                         (len % DAYSPERWEEK);
 404                                                 if (top < -3)
 405                                                         top += DAYSPERWEEK;
 406                                                 top += len;
 407                                                 if (yday >= top) {
 408                                                         ++base;
 409                                                         w = 1;
 410                                                         break;
 411                                                 }
 412                                                 if (yday >= bot) {
 413                                                         w = 1 + ((yday - bot) /
 414                                                                 DAYSPERWEEK);
 415                                                         break;
 416                                                 }
 417                                                 --base;
 418                                                 yday += isleap_sum(year, base) ?
 419                                                         DAYSPERLYEAR :
 420                                                         DAYSPERNYEAR;
 421                                         }
 422 #ifdef XPG4_1994_04_09
 423                                         if ((w == 52 &&
 424                                                 t->tm_mon == TM_JANUARY) ||
 425                                                 (w == 1 &&
 426                                                 t->tm_mon == TM_DECEMBER))
 427                                                         w = 53;
 428 #endif /* defined XPG4_1994_04_09 */
 429                                         if (*format == 'V')
 430                                                 pt = _conv(w, fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 431                                                         pt, ptlim, loc);
 432                                         else if (*format == 'g') {
 433                                                 *warnp = IN_ALL;
 434                                                 pt = _yconv(year, base, 0, 1,
 435                                                         pt, ptlim, loc);
 436                                         } else  pt = _yconv(year, base, 1, 1,
 437                                                         pt, ptlim, loc);
 438                                 }
 439                                 continue;
 440                         case 'v':
 441                                 /*
 442                                  * From Arnold Robbins' strftime version 3.0:
 443                                  * "date as dd-bbb-YYYY"
 444                                  * (ado, 1993-05-24)
 445                                  */
 446                                 pt = _fmt("%e-%b-%Y", t, pt, ptlim, warnp, loc);
 447                                 continue;
 448                         case 'W':
 449                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 450                                         (t->tm_wday ?
 451                                         (t->tm_wday - 1) :
 452                                         (DAYSPERWEEK - 1))) / DAYSPERWEEK,
 453                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 454                                         pt, ptlim, loc);
 455                                 continue;
 456                         case 'w':
 457                                 pt = _conv(t->tm_wday, "%d", pt, ptlim, loc);
 458                                 continue;
 459                         case 'X':
 460                                 pt = _fmt(tptr->X_fmt, t, pt, ptlim, warnp, loc);
 461                                 continue;
 462                         case 'x':
 463                                 {
 464                                 int     warn2 = IN_SOME;
 465
 466                                 pt = _fmt(tptr->x_fmt, t, pt, ptlim, &warn2, loc);
 467                                 if (warn2 == IN_ALL)
 468                                         warn2 = IN_THIS;
 469                                 if (warn2 > *warnp)
 470                                         *warnp = warn2;
 471                                 }
 472                                 continue;
 473                         case 'y':
 474                                 *warnp = IN_ALL;
 475                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 0, 1,
 476                                         pt, ptlim, loc);
 477                                 continue;
 478                         case 'Y':
 479                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 1,
 480                                         pt, ptlim, loc);
 481                                 continue;
 482                         case 'Z':
 483 #ifdef TM_ZONE
 484                                 if (t->TM_ZONE != NULL)
 485                                         pt = _add(t->TM_ZONE, pt, ptlim);
 486                                 else
 487 #endif /* defined TM_ZONE */
 488                                 if (t->tm_isdst >= 0)
 489                                         pt = _add(tzname[t->tm_isdst != 0],
 490                                                 pt, ptlim);
 491                                 /*
 492                                  * C99 says that %Z must be replaced by the
 493                                  * empty string if the time zone is not
 494                                  * determinable.
 495                                  */
 496                                 continue;
 497                         case 'z':
 498                                 {
 499                                 int             diff;
 500                                 char const *    sign;
 501
 502                                 if (t->tm_isdst < 0)
 503                                         continue;
 504 #ifdef TM_GMTOFF
 505                                 diff = t->TM_GMTOFF;
 506 #else /* !defined TM_GMTOFF */
 507                                 /*
 508                                  * C99 says that the UTC offset must
 509                                  * be computed by looking only at
 510                                  * tm_isdst. This requirement is
 511                                  * incorrect, since it means the code
 512                                  * must rely on magic (in this case
 513                                  * altzone and timezone), and the
 514                                  * magic might not have the correct
 515                                  * offset. Doing things correctly is
 516                                  * tricky and requires disobeying C99;
 517                                  * see GNU C strftime for details.
 518                                  * For now, punt and conform to the
 519                                  * standard, even though it's incorrect.
 520                                  *
 521                                  * C99 says that %z must be replaced by the
 522                                  * empty string if the time zone is not
 523                                  * determinable, so output nothing if the
 524                                  * appropriate variables are not available.
 525                                  */
 526                                 if (t->tm_isdst == 0)
 527 #ifdef USG_COMPAT
 528                                         diff = -timezone;
 529 #else /* !defined USG_COMPAT */
 530                                         continue;
 531 #endif /* !defined USG_COMPAT */
 532                                 else
 533 #ifdef ALTZONE
 534                                         diff = -altzone;
 535 #else /* !defined ALTZONE */
 536                                         continue;
 537 #endif /* !defined ALTZONE */
 538 #endif /* !defined TM_GMTOFF */
 539                                 if (diff < 0) {
 540                                         sign = "-";
 541                                         diff = -diff;
 542                                 } else
 543                                         sign = "+";
 544                                 pt = _add(sign, pt, ptlim);
 545                                 diff /= SECSPERMIN;
 546                                 diff = (diff / MINSPERHOUR) * 100 +
 547                                         (diff % MINSPERHOUR);
 548                                 pt = _conv(diff,
 549                                         fmt_padding[PAD_FMT_YEAR][PadIndex],
 550                                         pt, ptlim, loc);
 551                                 }
 552                                 continue;
 553                         case '+':
 554                                 pt = _fmt(tptr->date_fmt, t, pt, ptlim,
 555                                         warnp, loc);
 556                                 continue;
 557                         case '-':
 558                                 if (PadIndex != PAD_DEFAULT)
 559                                         break;
 560                                 PadIndex = PAD_LESS;
 561                                 goto label;
 562                         case '_':
 563                                 if (PadIndex != PAD_DEFAULT)
 564                                         break;
 565                                 PadIndex = PAD_SPACE;
 566                                 goto label;
 567                         case '0':
 568                                 if (PadIndex != PAD_DEFAULT)
 569                                         break;
 570                                 PadIndex = PAD_ZERO;
 571                                 goto label;
 572                         case '%':
 573                         /*
 574                          * X311J/88-090 (4.12.3.5): if conversion char is
 575                          * undefined, behavior is undefined. Print out the
 576                          * character itself as printf(3) also does.
 577                          */
 578                         default:
 579                                 break;
 580                         }
 581                 }
 582                 if (pt == ptlim)
 583                         break;
 584                 *pt++ = *format;
 585         }
 586         return (pt);
 587 }
 588
 589 static char *
 590 _conv(const int n, const char * const format, char * const pt,
 591     const char * const ptlim, locale_t  loc)
 592 {
 593         char    buf[INT_STRLEN_MAXIMUM(int) + 1];
 594
 595         (void) sprintf_l(buf, loc, format, n);
 596         return _add(buf, pt, ptlim);
 597 }
 598
 599 static char *
 600 _add(const char *str, char *pt, const char * const ptlim)
 601 {
 602         while (pt < ptlim && (*pt = *str++) != '\0')
 603                 ++pt;
 604         return (pt);
 605 }
 606
 607 /*
 608  * POSIX and the C Standard are unclear or inconsistent about
 609  * what %C and %y do if the year is negative or exceeds 9999.
 610  * Use the convention that %C concatenated with %y yields the
 611  * same output as %Y, and that %Y contains at least 4 bytes,
 612  * with more only if necessary.
 613  */
 614
 615 static char *
 616 _yconv(const int a, const int b, const int convert_top, const int convert_yy,
 617     char *pt, const char * const ptlim, locale_t  loc)
 618 {
 619         register int    lead;
 620         register int    trail;
 621
 622 #define DIVISOR 100
 623         trail = a % DIVISOR + b % DIVISOR;
 624         lead = a / DIVISOR + b / DIVISOR + trail / DIVISOR;
 625         trail %= DIVISOR;
 626         if (trail < 0 && lead > 0) {
 627                 trail += DIVISOR;
 628                 --lead;
 629         } else if (lead < 0 && trail > 0) {
 630                 trail -= DIVISOR;
 631                 ++lead;
 632         }
 633         if (convert_top) {
 634                 if (lead == 0 && trail < 0)
 635                         pt = _add("-0", pt, ptlim);
 636                 else    pt = _conv(lead, "%02d", pt, ptlim, loc);
 637         }
 638         if (convert_yy)
 639                 pt = _conv(((trail < 0) ? -trail : trail), "%02d", pt,
 640                      ptlim, loc);
 641         return (pt);
 642 }