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  *
   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 <stdio.h>
  46 #include "un-namespace.h"
  47 #include "timelocal.h"
  48
  49 static char *   _add(const char *, char *, const char *);
  50 static char *   _conv(int, const char *, char *, const char *, locale_t);
  51 static char *   _fmt(const char *, const struct tm *, char *, const char *,
  52                         int *, locale_t);
  53 static char *   _yconv(int, int, int, int, char *, const char *, locale_t);
  54
  55 extern char *   tzname[];
  56
  57 #ifndef YEAR_2000_NAME
  58 #define YEAR_2000_NAME  "CHECK_STRFTIME_FORMATS_FOR_TWO_DIGIT_YEARS"
  59 #endif /* !defined YEAR_2000_NAME */
  60
  61 #define IN_NONE 0
  62 #define IN_SOME 1
  63 #define IN_THIS 2
  64 #define IN_ALL  3
  65
  66 #define PAD_DEFAULT     0
  67 #define PAD_LESS        1
  68 #define PAD_SPACE       2
  69 #define PAD_ZERO        3
  70
  71 static const char fmt_padding[][4][5] = {
  72         /* DEFAULT,     LESS,   SPACE,  ZERO */
  73 #define PAD_FMT_MONTHDAY        0
  74 #define PAD_FMT_HMS             0
  75 #define PAD_FMT_CENTURY         0
  76 #define PAD_FMT_SHORTYEAR       0
  77 #define PAD_FMT_MONTH           0
  78 #define PAD_FMT_WEEKOFYEAR      0
  79 #define PAD_FMT_DAYOFMONTH      0
  80         { "%02d",       "%d",   "%2d",  "%02d" },
  81 #define PAD_FMT_SDAYOFMONTH     1
  82 #define PAD_FMT_SHMS            1
  83         { "%2d",        "%d",   "%2d",  "%02d" },
  84 #define PAD_FMT_DAYOFYEAR       2
  85         { "%03d",       "%d",   "%3d",  "%03d" },
  86 #define PAD_FMT_YEAR            3
  87         { "%04d",       "%d",   "%4d",  "%04d" }
  88 };
  89
  90 size_t
  91 strftime_l(char * __restrict s, size_t maxsize, const char * __restrict format,
  92     const struct tm * __restrict t, locale_t loc)
  93 {
  94         char *  p;
  95         int     warn;
  96         FIX_LOCALE(loc);
  97
  98         tzset();
  99         warn = IN_NONE;
 100         p = _fmt(((format == NULL) ? "%c" : format), t, s, s + maxsize, &warn, loc);
 101 #ifndef NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU
 102         if (warn != IN_NONE && getenv(YEAR_2000_NAME) != NULL) {
 103                 (void) fprintf_l(stderr, loc, "\n");
 104                 if (format == NULL)
 105                         (void) fputs("NULL strftime format ", stderr);
 106                 else    (void) fprintf_l(stderr, loc, "strftime format \"%s\" ",
 107                                 format);
 108                 (void) fputs("yields only two digits of years in ", stderr);
 109                 if (warn == IN_SOME)
 110                         (void) fputs("some locales", stderr);
 111                 else if (warn == IN_THIS)
 112                         (void) fputs("the current locale", stderr);
 113                 else    (void) fputs("all locales", stderr);
 114                 (void) fputs("\n", stderr);
 115         }
 116 #endif /* !defined NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU */
 117         if (p == s + maxsize)
 118                 return (0);
 119         *p = '\0';
 120         return p - s;
 121 }
 122
 123 size_t
 124 strftime(char * __restrict s, size_t maxsize, const char * __restrict format,
 125     const struct tm * __restrict t)
 126 {
 127         return strftime_l(s, maxsize, format, t, __get_locale());
 128 }
 129
 130 static char *
 131 _fmt(const char *format, const struct tm * const t, char *pt,
 132     const char * const ptlim, int *warnp, locale_t loc)
 133 {
 134         int Ealternative, Oalternative, PadIndex;
 135         struct lc_time_T *tptr = __get_current_time_locale(loc);
 136
 137         for ( ; *format; ++format) {
 138                 if (*format == '%') {
 139                         Ealternative = 0;
 140                         Oalternative = 0;
 141                         PadIndex         = PAD_DEFAULT;
 142 label:
 143                         switch (*++format) {
 144                         case '\0':
 145                                 --format;
 146                                 break;
 147                         case 'A':
 148                                 pt = _add((t->tm_wday < 0 ||
 149                                         t->tm_wday >= DAYSPERWEEK) ?
 150                                         "?" : tptr->weekday[t->tm_wday],
 151                                         pt, ptlim);
 152                                 continue;
 153                         case 'a':
 154                                 pt = _add((t->tm_wday < 0 ||
 155                                         t->tm_wday >= DAYSPERWEEK) ?
 156                                         "?" : tptr->wday[t->tm_wday],
 157                                         pt, ptlim);
 158                                 continue;
 159                         case 'B':
 160                                 pt = _add((t->tm_mon < 0 ||
 161                                         t->tm_mon >= MONSPERYEAR) ?
 162                                         "?" : (Oalternative ? tptr->alt_month :
 163                                         tptr->month)[t->tm_mon],
 164                                         pt, ptlim);
 165                                 continue;
 166                         case 'b':
 167                         case 'h':
 168                                 pt = _add((t->tm_mon < 0 ||
 169                                         t->tm_mon >= MONSPERYEAR) ?
 170                                         "?" : tptr->mon[t->tm_mon],
 171                                         pt, ptlim);
 172                                 continue;
 173                         case 'C':
 174                                 /*
 175                                  * %C used to do a...
 176                                  *      _fmt("%a %b %e %X %Y", t);
 177                                  * ...whereas now POSIX 1003.2 calls for
 178                                  * something completely different.
 179                                  * (ado, 1993-05-24)
 180                                  */
 181                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 0,
 182                                         pt, ptlim, loc);
 183                                 continue;
 184                         case 'c':
 185                                 {
 186                                 int warn2 = IN_SOME;
 187
 188                                 pt = _fmt(tptr->c_fmt, t, pt, ptlim, &warn2, loc);
 189                                 if (warn2 == IN_ALL)
 190                                         warn2 = IN_THIS;
 191                                 if (warn2 > *warnp)
 192                                         *warnp = warn2;
 193                                 }
 194                                 continue;
 195                         case 'D':
 196                                 pt = _fmt("%m/%d/%y", t, pt, ptlim, warnp, loc);
 197                                 continue;
 198                         case 'd':
 199                                 pt = _conv(t->tm_mday,
 200                                         fmt_padding[PAD_FMT_DAYOFMONTH][PadIndex],
 201                                         pt, ptlim, loc);
 202                                 continue;
 203                         case 'E':
 204                                 if (Ealternative || Oalternative)
 205                                         break;
 206                                 Ealternative++;
 207                                 goto label;
 208                         case 'O':
 209                                 /*
 210                                  * C99 locale modifiers.
 211                                  * The sequences
 212                                  *      %Ec %EC %Ex %EX %Ey %EY
 213                                  *      %Od %oe %OH %OI %Om %OM
 214                                  *      %OS %Ou %OU %OV %Ow %OW %Oy
 215                                  * are supposed to provide alternate
 216                                  * representations.
 217                                  *
 218                                  * FreeBSD extension
 219                                  *      %OB
 220                                  */
 221                                 if (Ealternative || Oalternative)
 222                                         break;
 223                                 Oalternative++;
 224                                 goto label;
 225                         case 'e':
 226                                 pt = _conv(t->tm_mday,
 227                                         fmt_padding[PAD_FMT_SDAYOFMONTH][PadIndex],
 228                                         pt, ptlim, loc);
 229                                 continue;
 230                         case 'F':
 231                                 pt = _fmt("%Y-%m-%d", t, pt, ptlim, warnp, loc);
 232                                 continue;
 233                         case 'H':
 234                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_HMS][PadIndex],
 235                                         pt, ptlim, loc);
 236                                 continue;
 237                         case 'I':
 238                                 pt = _conv((t->tm_hour % 12) ?
 239                                         (t->tm_hour % 12) : 12,
 240                                         fmt_padding[PAD_FMT_HMS][PadIndex],
 241                                         pt, ptlim, loc);
 242                                 continue;
 243                         case 'j':
 244                                 pt = _conv(t->tm_yday + 1,
 245                                         fmt_padding[PAD_FMT_DAYOFYEAR][PadIndex],
 246                                         pt, ptlim, loc);
 247                                 continue;
 248                         case 'k':
 249                                 /*
 250                                  * This used to be...
 251                                  *      _conv(t->tm_hour % 12 ?
 252                                  *              t->tm_hour % 12 : 12, 2, ' ');
 253                                  * ...and has been changed to the below to
 254                                  * match SunOS 4.1.1 and Arnold Robbins'
 255                                  * strftime version 3.0. That is, "%k" and
 256                                  * "%l" have been swapped.
 257                                  * (ado, 1993-05-24)
 258                                  */
 259                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_SHMS][PadIndex],
 260                                         pt, ptlim, loc);
 261                                 continue;
 262 #ifdef KITCHEN_SINK
 263                         case 'K':
 264                                 /*
 265                                 ** After all this time, still unclaimed!
 266                                 */
 267                                 pt = _add("kitchen sink", pt, ptlim);
 268                                 continue;
 269 #endif /* defined KITCHEN_SINK */
 270                         case 'l':
 271                                 /*
 272                                  * This used to be...
 273                                  *      _conv(t->tm_hour, 2, ' ');
 274                                  * ...and has been changed to the below to
 275                                  * match SunOS 4.1.1 and Arnold Robbin's
 276                                  * strftime version 3.0. That is, "%k" and
 277                                  * "%l" have been swapped.
 278                                  * (ado, 1993-05-24)
 279                                  */
 280                                 pt = _conv((t->tm_hour % 12) ?
 281                                         (t->tm_hour % 12) : 12,
 282                                         fmt_padding[PAD_FMT_SHMS][PadIndex],
 283                                         pt, ptlim, loc);
 284                                 continue;
 285                         case 'M':
 286                                 pt = _conv(t->tm_min, fmt_padding[PAD_FMT_HMS][PadIndex],
 287                                         pt, ptlim, loc);
 288                                 continue;
 289                         case 'm':
 290                                 pt = _conv(t->tm_mon + 1,
 291                                         fmt_padding[PAD_FMT_MONTH][PadIndex],
 292                                         pt, ptlim, loc);
 293                                 continue;
 294                         case 'n':
 295                                 pt = _add("\n", pt, ptlim);
 296                                 continue;
 297                         case 'p':
 298                                 pt = _add((t->tm_hour >= (HOURSPERDAY / 2)) ?
 299                                         tptr->pm : tptr->am,
 300                                         pt, ptlim);
 301                                 continue;
 302                         case 'R':
 303                                 pt = _fmt("%H:%M", t, pt, ptlim, warnp, loc);
 304                                 continue;
 305                         case 'r':
 306                                 pt = _fmt(tptr->ampm_fmt, t, pt, ptlim,
 307                                         warnp, loc);
 308                                 continue;
 309                         case 'S':
 310                                 pt = _conv(t->tm_sec, fmt_padding[PAD_FMT_HMS][PadIndex],
 311                                         pt, ptlim, loc);
 312                                 continue;
 313                         case 's':
 314                                 {
 315                                         struct tm       tm;
 316                                         char            buf[INT_STRLEN_MAXIMUM(
 317                                                                 time_t) + 1];
 318                                         time_t          mkt;
 319
 320                                         tm = *t;
 321                                         mkt = mktime(&tm);
 322                                         if (TYPE_SIGNED(time_t))
 323                                                 (void) sprintf_l(buf, loc, "%ld",
 324                                                         (long) mkt);
 325                                         else    (void) sprintf_l(buf, loc, "%lu",
 326                                                         (unsigned long) mkt);
 327                                         pt = _add(buf, pt, ptlim);
 328                                 }
 329                                 continue;
 330                         case 'T':
 331                                 pt = _fmt("%H:%M:%S", t, pt, ptlim, warnp, loc);
 332                                 continue;
 333                         case 't':
 334                                 pt = _add("\t", pt, ptlim);
 335                                 continue;
 336                         case 'U':
 337                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 338                                         t->tm_wday) / DAYSPERWEEK,
 339                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 340                                         pt, ptlim, loc);
 341                                 continue;
 342                         case 'u':
 343                                 /*
 344                                  * From Arnold Robbins' strftime version 3.0:
 345                                  * "ISO 8601: Weekday as a decimal number
 346                                  * [1 (Monday) - 7]"
 347                                  * (ado, 1993-05-24)
 348                                  */
 349                                 pt = _conv((t->tm_wday == 0) ?
 350                                         DAYSPERWEEK : t->tm_wday,
 351                                         "%d", pt, ptlim, loc);
 352                                 continue;
 353                         case 'V':       /* ISO 8601 week number */
 354                         case 'G':       /* ISO 8601 year (four digits) */
 355                         case 'g':       /* ISO 8601 year (two digits) */
 356 /*
 357  * From Arnold Robbins' strftime version 3.0: "the week number of the
 358  * year (the first Monday as the first day of week 1) as a decimal number
 359  * (01-53)."
 360  * (ado, 1993-05-24)
 361  *
 362  * From "http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html" by Markus Kuhn:
 363  * "Week 01 of a year is per definition the first week which has the
 364  * Thursday in this year, which is equivalent to the week which contains
 365  * the fourth day of January. In other words, the first week of a new year
 366  * is the week which has the majority of its days in the new year. Week 01
 367  * might also contain days from the previous year and the week before week
 368  * 01 of a year is the last week (52 or 53) of the previous year even if
 369  * it contains days from the new year. A week starts with Monday (day 1)
 370  * and ends with Sunday (day 7). For example, the first week of the year
 371  * 1997 lasts from 1996-12-30 to 1997-01-05..."
 372  * (ado, 1996-01-02)
 373  */
 374                                 {
 375                                         int     year;
 376                                         int     base;
 377                                         int     yday;
 378                                         int     wday;
 379                                         int     w;
 380
 381                                         year = t->tm_year;
 382                                         base = TM_YEAR_BASE;
 383                                         yday = t->tm_yday;
 384                                         wday = t->tm_wday;
 385                                         for ( ; ; ) {
 386                                                 int     len;
 387                                                 int     bot;
 388                                                 int     top;
 389
 390                                                 len = isleap_sum(year, base) ?
 391                                                         DAYSPERLYEAR :
 392                                                         DAYSPERNYEAR;
 393                                                 /*
 394                                                  * What yday (-3 ... 3) does
 395                                                  * the ISO year begin on?
 396                                                  */
 397                                                 bot = ((yday + 11 - wday) %
 398                                                         DAYSPERWEEK) - 3;
 399                                                 /*
 400                                                  * What yday does the NEXT
 401                                                  * ISO year begin on?
 402                                                  */
 403                                                 top = bot -
 404                                                         (len % DAYSPERWEEK);
 405                                                 if (top < -3)
 406                                                         top += DAYSPERWEEK;
 407                                                 top += len;
 408                                                 if (yday >= top) {
 409                                                         ++base;
 410                                                         w = 1;
 411                                                         break;
 412                                                 }
 413                                                 if (yday >= bot) {
 414                                                         w = 1 + ((yday - bot) /
 415                                                                 DAYSPERWEEK);
 416                                                         break;
 417                                                 }
 418                                                 --base;
 419                                                 yday += isleap_sum(year, base) ?
 420                                                         DAYSPERLYEAR :
 421                                                         DAYSPERNYEAR;
 422                                         }
 423 #ifdef XPG4_1994_04_09
 424                                         if ((w == 52 &&
 425                                                 t->tm_mon == TM_JANUARY) ||
 426                                                 (w == 1 &&
 427                                                 t->tm_mon == TM_DECEMBER))
 428                                                         w = 53;
 429 #endif /* defined XPG4_1994_04_09 */
 430                                         if (*format == 'V')
 431                                                 pt = _conv(w, fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 432                                                         pt, ptlim, loc);
 433                                         else if (*format == 'g') {
 434                                                 *warnp = IN_ALL;
 435                                                 pt = _yconv(year, base, 0, 1,
 436                                                         pt, ptlim, loc);
 437                                         } else  pt = _yconv(year, base, 1, 1,
 438                                                         pt, ptlim, loc);
 439                                 }
 440                                 continue;
 441                         case 'v':
 442                                 /*
 443                                  * From Arnold Robbins' strftime version 3.0:
 444                                  * "date as dd-bbb-YYYY"
 445                                  * (ado, 1993-05-24)
 446                                  */
 447                                 pt = _fmt("%e-%b-%Y", t, pt, ptlim, warnp, loc);
 448                                 continue;
 449                         case 'W':
 450                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 451                                         (t->tm_wday ?
 452                                         (t->tm_wday - 1) :
 453                                         (DAYSPERWEEK - 1))) / DAYSPERWEEK,
 454                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 455                                         pt, ptlim, loc);
 456                                 continue;
 457                         case 'w':
 458                                 pt = _conv(t->tm_wday, "%d", pt, ptlim, loc);
 459                                 continue;
 460                         case 'X':
 461                                 pt = _fmt(tptr->X_fmt, t, pt, ptlim, warnp, loc);
 462                                 continue;
 463                         case 'x':
 464                                 {
 465                                 int     warn2 = IN_SOME;
 466
 467                                 pt = _fmt(tptr->x_fmt, t, pt, ptlim, &warn2, loc);
 468                                 if (warn2 == IN_ALL)
 469                                         warn2 = IN_THIS;
 470                                 if (warn2 > *warnp)
 471                                         *warnp = warn2;
 472                                 }
 473                                 continue;
 474                         case 'y':
 475                                 *warnp = IN_ALL;
 476                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 0, 1,
 477                                         pt, ptlim, loc);
 478                                 continue;
 479                         case 'Y':
 480                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 1,
 481                                         pt, ptlim, loc);
 482                                 continue;
 483                         case 'Z':
 484 #ifdef TM_ZONE
 485                                 if (t->TM_ZONE != NULL)
 486                                         pt = _add(t->TM_ZONE, pt, ptlim);
 487                                 else
 488 #endif /* defined TM_ZONE */
 489                                 if (t->tm_isdst >= 0)
 490                                         pt = _add(tzname[t->tm_isdst != 0],
 491                                                 pt, ptlim);
 492                                 /*
 493                                  * C99 says that %Z must be replaced by the
 494                                  * empty string if the time zone is not
 495                                  * determinable.
 496                                  */
 497                                 continue;
 498                         case 'z':
 499                                 {
 500                                 int             diff;
 501                                 char const *    sign;
 502
 503                                 if (t->tm_isdst < 0)
 504                                         continue;
 505 #ifdef TM_GMTOFF
 506                                 diff = t->TM_GMTOFF;
 507 #else /* !defined TM_GMTOFF */
 508                                 /*
 509                                  * C99 says that the UTC offset must
 510                                  * be computed by looking only at
 511                                  * tm_isdst. This requirement is
 512                                  * incorrect, since it means the code
 513                                  * must rely on magic (in this case
 514                                  * altzone and timezone), and the
 515                                  * magic might not have the correct
 516                                  * offset. Doing things correctly is
 517                                  * tricky and requires disobeying C99;
 518                                  * see GNU C strftime for details.
 519                                  * For now, punt and conform to the
 520                                  * standard, even though it's incorrect.
 521                                  *
 522                                  * C99 says that %z must be replaced by the
 523                                  * empty string if the time zone is not
 524                                  * determinable, so output nothing if the
 525                                  * appropriate variables are not available.
 526                                  */
 527                                 if (t->tm_isdst == 0)
 528 #ifdef USG_COMPAT
 529                                         diff = -timezone;
 530 #else /* !defined USG_COMPAT */
 531                                         continue;
 532 #endif /* !defined USG_COMPAT */
 533                                 else
 534 #ifdef ALTZONE
 535                                         diff = -altzone;
 536 #else /* !defined ALTZONE */
 537                                         continue;
 538 #endif /* !defined ALTZONE */
 539 #endif /* !defined TM_GMTOFF */
 540                                 if (diff < 0) {
 541                                         sign = "-";
 542                                         diff = -diff;
 543                                 } else
 544                                         sign = "+";
 545                                 pt = _add(sign, pt, ptlim);
 546                                 diff /= SECSPERMIN;
 547                                 diff = (diff / MINSPERHOUR) * 100 +
 548                                         (diff % MINSPERHOUR);
 549                                 pt = _conv(diff,
 550                                         fmt_padding[PAD_FMT_YEAR][PadIndex],
 551                                         pt, ptlim, loc);
 552                                 }
 553                                 continue;
 554                         case '+':
 555                                 pt = _fmt(tptr->date_fmt, t, pt, ptlim,
 556                                         warnp, loc);
 557                                 continue;
 558                         case '-':
 559                                 if (PadIndex != PAD_DEFAULT)
 560                                         break;
 561                                 PadIndex = PAD_LESS;
 562                                 goto label;
 563                         case '_':
 564                                 if (PadIndex != PAD_DEFAULT)
 565                                         break;
 566                                 PadIndex = PAD_SPACE;
 567                                 goto label;
 568                         case '0':
 569                                 if (PadIndex != PAD_DEFAULT)
 570                                         break;
 571                                 PadIndex = PAD_ZERO;
 572                                 goto label;
 573                         case '%':
 574                         /*
 575                          * X311J/88-090 (4.12.3.5): if conversion char is
 576                          * undefined, behavior is undefined. Print out the
 577                          * character itself as printf(3) also does.
 578                          */
 579                         default:
 580                                 break;
 581                         }
 582                 }
 583                 if (pt == ptlim)
 584                         break;
 585                 *pt++ = *format;
 586         }
 587         return (pt);
 588 }
 589
 590 static char *
 591 _conv(const int n, const char * const format, char * const pt,
 592     const char * const ptlim, locale_t  loc)
 593 {
 594         char    buf[INT_STRLEN_MAXIMUM(int) + 1];
 595
 596         (void) sprintf_l(buf, loc, format, n);
 597         return _add(buf, pt, ptlim);
 598 }
 599
 600 static char *
 601 _add(const char *str, char *pt, const char * const ptlim)
 602 {
 603         while (pt < ptlim && (*pt = *str++) != '\0')
 604                 ++pt;
 605         return (pt);
 606 }
 607
 608 /*
 609  * POSIX and the C Standard are unclear or inconsistent about
 610  * what %C and %y do if the year is negative or exceeds 9999.
 611  * Use the convention that %C concatenated with %y yields the
 612  * same output as %Y, and that %Y contains at least 4 bytes,
 613  * with more only if necessary.
 614  */
 615
 616 static char *
 617 _yconv(const int a, const int b, const int convert_top, const int convert_yy,
 618     char *pt, const char * const ptlim, locale_t  loc)
 619 {
 620         register int    lead;
 621         register int    trail;
 622
 623 #define DIVISOR 100
 624         trail = a % DIVISOR + b % DIVISOR;
 625         lead = a / DIVISOR + b / DIVISOR + trail / DIVISOR;
 626         trail %= DIVISOR;
 627         if (trail < 0 && lead > 0) {
 628                 trail += DIVISOR;
 629                 --lead;
 630         } else if (lead < 0 && trail > 0) {
 631                 trail -= DIVISOR;
 632                 ++lead;
 633         }
 634         if (convert_top) {
 635                 if (lead == 0 && trail < 0)
 636                         pt = _add("-0", pt, ptlim);
 637                 else    pt = _conv(lead, "%02d", pt, ptlim, loc);
 638         }
 639         if (convert_yy)
 640                 pt = _conv(((trail < 0) ? -trail : trail), "%02d", pt,
 641                      ptlim, loc);
 642         return (pt);
 643 }