lib/libc/stdtime/strftime.c

   1 /*
   2  * Copyright (c) 1989 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms are permitted
   6  * provided that the above copyright notice and this paragraph are
   7  * duplicated in all such forms and that any documentation,
   8  * advertising materials, and other materials related to such
   9  * distribution and use acknowledge that the software was developed
  10  * by the University of California, Berkeley. The name of the
  11  * University may not be used to endorse or promote products derived
  12  * from this software without specific prior written permission.
  13  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  15  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  16  */
  17
  18 #ifndef lint
  19 #ifndef NOID
  20 static const char       elsieid[] = "@(#)strftime.3     8.3";
  21 /*
  22 ** Based on the UCB version with the ID appearing below.
  23 ** This is ANSIish only when "multibyte character == plain character".
  24 */
  25 #endif /* !defined NOID */
  26 #endif /* !defined lint */
  27
  28 #include "namespace.h"
  29 #include "private.h"
  30
  31 #if defined(LIBC_SCCS) && !defined(lint)
  32 static const char       sccsid[] = "@(#)strftime.c      5.4 (Berkeley) 3/14/89";
  33 #endif /* LIBC_SCCS and not lint */
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "tzfile.h"
  38 #include <fcntl.h>
  39 #include <sys/stat.h>
  40 #include "un-namespace.h"
  41 #include "timelocal.h"
  42
  43 static char *   _add(const char *, char *, const char *);
  44 static char *   _conv(int, const char *, char *, const char *);
  45 static char *   _fmt(const char *, const struct tm *, char *, const char *,
  46                         int *);
  47 static char *   _yconv(int, int, int, int, char *, const char *);
  48
  49 extern char *   tzname[];
  50
  51 #ifndef YEAR_2000_NAME
  52 #define YEAR_2000_NAME  "CHECK_STRFTIME_FORMATS_FOR_TWO_DIGIT_YEARS"
  53 #endif /* !defined YEAR_2000_NAME */
  54
  55 #define IN_NONE 0
  56 #define IN_SOME 1
  57 #define IN_THIS 2
  58 #define IN_ALL  3
  59
  60 #define PAD_DEFAULT     0
  61 #define PAD_LESS        1
  62 #define PAD_SPACE       2
  63 #define PAD_ZERO        3
  64
  65 static const char* fmt_padding[][4] = {
  66         /* DEFAULT,     LESS,   SPACE,  ZERO */
  67 #define PAD_FMT_MONTHDAY        0
  68 #define PAD_FMT_HMS             0
  69 #define PAD_FMT_CENTURY         0
  70 #define PAD_FMT_SHORTYEAR       0
  71 #define PAD_FMT_MONTH           0
  72 #define PAD_FMT_WEEKOFYEAR      0
  73 #define PAD_FMT_DAYOFMONTH      0
  74         { "%02d",       "%d",   "%2d",  "%02d" },
  75 #define PAD_FMT_SDAYOFMONTH     1
  76 #define PAD_FMT_SHMS            1
  77         { "%2d",        "%d",   "%2d",  "%02d" },
  78 #define PAD_FMT_DAYOFYEAR       2
  79         { "%03d",       "%d",   "%3d",  "%03d" },
  80 #define PAD_FMT_YEAR            3
  81         { "%04d",       "%d",   "%4d",  "%04d" }
  82 };
  83
  84 size_t
  85 strftime(char * __restrict s, size_t maxsize, const char * __restrict format,
  86     const struct tm * __restrict t)
  87 {
  88         char *  p;
  89         int     warn;
  90
  91         tzset();
  92         warn = IN_NONE;
  93         p = _fmt(((format == NULL) ? "%c" : format), t, s, s + maxsize, &warn);
  94 #ifndef NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU
  95         if (warn != IN_NONE && getenv(YEAR_2000_NAME) != NULL) {
  96                 (void) fprintf(stderr, "\n");
  97                 if (format == NULL)
  98                         (void) fprintf(stderr, "NULL strftime format ");
  99                 else    (void) fprintf(stderr, "strftime format \"%s\" ",
 100                                 format);
 101                 (void) fprintf(stderr, "yields only two digits of years in ");
 102                 if (warn == IN_SOME)
 103                         (void) fprintf(stderr, "some locales");
 104                 else if (warn == IN_THIS)
 105                         (void) fprintf(stderr, "the current locale");
 106                 else    (void) fprintf(stderr, "all locales");
 107                 (void) fprintf(stderr, "\n");
 108         }
 109 #endif /* !defined NO_RUN_TIME_WARNINGS_ABOUT_YEAR_2000_PROBLEMS_THANK_YOU */
 110         if (p == s + maxsize)
 111                 return 0;
 112         *p = '\0';
 113         return p - s;
 114 }
 115
 116 static char *
 117 _fmt(format, t, pt, ptlim, warnp)
 118 const char *            format;
 119 const struct tm * const t;
 120 char *                  pt;
 121 const char * const      ptlim;
 122 int *                   warnp;
 123 {
 124         int Ealternative, Oalternative, PadIndex;
 125         struct lc_time_T *tptr = __get_current_time_locale();
 126
 127         for ( ; *format; ++format) {
 128                 if (*format == '%') {
 129                         Ealternative = 0;
 130                         Oalternative = 0;
 131                         PadIndex         = PAD_DEFAULT;
 132 label:
 133                         switch (*++format) {
 134                         case '\0':
 135                                 --format;
 136                                 break;
 137                         case 'A':
 138                                 pt = _add((t->tm_wday < 0 ||
 139                                         t->tm_wday >= DAYSPERWEEK) ?
 140                                         "?" : tptr->weekday[t->tm_wday],
 141                                         pt, ptlim);
 142                                 continue;
 143                         case 'a':
 144                                 pt = _add((t->tm_wday < 0 ||
 145                                         t->tm_wday >= DAYSPERWEEK) ?
 146                                         "?" : tptr->wday[t->tm_wday],
 147                                         pt, ptlim);
 148                                 continue;
 149                         case 'B':
 150                                 pt = _add((t->tm_mon < 0 ||
 151                                         t->tm_mon >= MONSPERYEAR) ?
 152                                         "?" : (Oalternative ? tptr->alt_month :
 153                                         tptr->month)[t->tm_mon],
 154                                         pt, ptlim);
 155                                 continue;
 156                         case 'b':
 157                         case 'h':
 158                                 pt = _add((t->tm_mon < 0 ||
 159                                         t->tm_mon >= MONSPERYEAR) ?
 160                                         "?" : tptr->mon[t->tm_mon],
 161                                         pt, ptlim);
 162                                 continue;
 163                         case 'C':
 164                                 /*
 165                                 ** %C used to do a...
 166                                 **      _fmt("%a %b %e %X %Y", t);
 167                                 ** ...whereas now POSIX 1003.2 calls for
 168                                 ** something completely different.
 169                                 ** (ado, 1993-05-24)
 170                                 */
 171                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 0,
 172                                         pt, ptlim);
 173                                 continue;
 174                         case 'c':
 175                                 {
 176                                 int warn2 = IN_SOME;
 177
 178                                 pt = _fmt(tptr->c_fmt, t, pt, ptlim, &warn2);
 179                                 if (warn2 == IN_ALL)
 180                                         warn2 = IN_THIS;
 181                                 if (warn2 > *warnp)
 182                                         *warnp = warn2;
 183                                 }
 184                                 continue;
 185                         case 'D':
 186                                 pt = _fmt("%m/%d/%y", t, pt, ptlim, warnp);
 187                                 continue;
 188                         case 'd':
 189                                 pt = _conv(t->tm_mday, fmt_padding[PAD_FMT_DAYOFMONTH][PadIndex],
 190                                         pt, ptlim);
 191                                 continue;
 192                         case 'E':
 193                                 if (Ealternative || Oalternative)
 194                                         break;
 195                                 Ealternative++;
 196                                 goto label;
 197                         case 'O':
 198                                 /*
 199                                 ** C99 locale modifiers.
 200                                 ** The sequences
 201                                 **      %Ec %EC %Ex %EX %Ey %EY
 202                                 **      %Od %oe %OH %OI %Om %OM
 203                                 **      %OS %Ou %OU %OV %Ow %OW %Oy
 204                                 ** are supposed to provide alternate
 205                                 ** representations.
 206                                 **
 207                                 ** FreeBSD extension
 208                                 **      %OB
 209                                 */
 210                                 if (Ealternative || Oalternative)
 211                                         break;
 212                                 Oalternative++;
 213                                 goto label;
 214                         case 'e':
 215                                 pt = _conv(t->tm_mday,
 216                                         fmt_padding[PAD_FMT_SDAYOFMONTH][PadIndex], pt, ptlim);
 217                                 continue;
 218                         case 'F':
 219                                 pt = _fmt("%Y-%m-%d", t, pt, ptlim, warnp);
 220                                 continue;
 221                         case 'H':
 222                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_HMS][PadIndex],
 223                                         pt, ptlim);
 224                                 continue;
 225                         case 'I':
 226                                 pt = _conv((t->tm_hour % 12) ?
 227                                         (t->tm_hour % 12) : 12,
 228                                         fmt_padding[PAD_FMT_HMS][PadIndex], pt, ptlim);
 229                                 continue;
 230                         case 'j':
 231                                 pt = _conv(t->tm_yday + 1,
 232                                         fmt_padding[PAD_FMT_DAYOFYEAR][PadIndex], pt, ptlim);
 233                                 continue;
 234                         case 'k':
 235                                 /*
 236                                 ** This used to be...
 237                                 **      _conv(t->tm_hour % 12 ?
 238                                 **              t->tm_hour % 12 : 12, 2, ' ');
 239                                 ** ...and has been changed to the below to
 240                                 ** match SunOS 4.1.1 and Arnold Robbins'
 241                                 ** strftime version 3.0. That is, "%k" and
 242                                 ** "%l" have been swapped.
 243                                 ** (ado, 1993-05-24)
 244                                 */
 245                                 pt = _conv(t->tm_hour, fmt_padding[PAD_FMT_SHMS][PadIndex],
 246                                         pt, ptlim);
 247                                 continue;
 248 #ifdef KITCHEN_SINK
 249                         case 'K':
 250                                 /*
 251                                 ** After all this time, still unclaimed!
 252                                 */
 253                                 pt = _add("kitchen sink", pt, ptlim);
 254                                 continue;
 255 #endif /* defined KITCHEN_SINK */
 256                         case 'l':
 257                                 /*
 258                                 ** This used to be...
 259                                 **      _conv(t->tm_hour, 2, ' ');
 260                                 ** ...and has been changed to the below to
 261                                 ** match SunOS 4.1.1 and Arnold Robbin's
 262                                 ** strftime version 3.0. That is, "%k" and
 263                                 ** "%l" have been swapped.
 264                                 ** (ado, 1993-05-24)
 265                                 */
 266                                 pt = _conv((t->tm_hour % 12) ?
 267                                         (t->tm_hour % 12) : 12,
 268                                         fmt_padding[PAD_FMT_SHMS][PadIndex], pt, ptlim);
 269                                 continue;
 270                         case 'M':
 271                                 pt = _conv(t->tm_min, fmt_padding[PAD_FMT_HMS][PadIndex],
 272                                         pt, ptlim);
 273                                 continue;
 274                         case 'm':
 275                                 pt = _conv(t->tm_mon + 1,
 276                                         fmt_padding[PAD_FMT_MONTH][PadIndex], pt, ptlim);
 277                                 continue;
 278                         case 'n':
 279                                 pt = _add("\n", pt, ptlim);
 280                                 continue;
 281                         case 'p':
 282                                 pt = _add((t->tm_hour >= (HOURSPERDAY / 2)) ?
 283                                         tptr->pm :
 284                                         tptr->am,
 285                                         pt, ptlim);
 286                                 continue;
 287                         case 'R':
 288                                 pt = _fmt("%H:%M", t, pt, ptlim, warnp);
 289                                 continue;
 290                         case 'r':
 291                                 pt = _fmt(tptr->ampm_fmt, t, pt, ptlim,
 292                                         warnp);
 293                                 continue;
 294                         case 'S':
 295                                 pt = _conv(t->tm_sec, fmt_padding[PAD_FMT_HMS][PadIndex],
 296                                         pt, ptlim);
 297                                 continue;
 298                         case 's':
 299                                 {
 300                                         struct tm       tm;
 301                                         char            buf[INT_STRLEN_MAXIMUM(
 302                                                                 time_t) + 1];
 303                                         time_t          mkt;
 304
 305                                         tm = *t;
 306                                         mkt = mktime(&tm);
 307                                         if (TYPE_SIGNED(time_t))
 308                                                 (void) sprintf(buf, "%ld",
 309                                                         (long) mkt);
 310                                         else    (void) sprintf(buf, "%lu",
 311                                                         (unsigned long) mkt);
 312                                         pt = _add(buf, pt, ptlim);
 313                                 }
 314                                 continue;
 315                         case 'T':
 316                                 pt = _fmt("%H:%M:%S", t, pt, ptlim, warnp);
 317                                 continue;
 318                         case 't':
 319                                 pt = _add("\t", pt, ptlim);
 320                                 continue;
 321                         case 'U':
 322                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 323                                         t->tm_wday) / DAYSPERWEEK,
 324                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex], pt, ptlim);
 325                                 continue;
 326                         case 'u':
 327                                 /*
 328                                 ** From Arnold Robbins' strftime version 3.0:
 329                                 ** "ISO 8601: Weekday as a decimal number
 330                                 ** [1 (Monday) - 7]"
 331                                 ** (ado, 1993-05-24)
 332                                 */
 333                                 pt = _conv((t->tm_wday == 0) ?
 334                                         DAYSPERWEEK : t->tm_wday,
 335                                         "%d", pt, ptlim);
 336                                 continue;
 337                         case 'V':       /* ISO 8601 week number */
 338                         case 'G':       /* ISO 8601 year (four digits) */
 339                         case 'g':       /* ISO 8601 year (two digits) */
 340 /*
 341 ** From Arnold Robbins' strftime version 3.0: "the week number of the
 342 ** year (the first Monday as the first day of week 1) as a decimal number
 343 ** (01-53)."
 344 ** (ado, 1993-05-24)
 345 **
 346 ** From "http://www.ft.uni-erlangen.de/~mskuhn/iso-time.html" by Markus Kuhn:
 347 ** "Week 01 of a year is per definition the first week which has the
 348 ** Thursday in this year, which is equivalent to the week which contains
 349 ** the fourth day of January. In other words, the first week of a new year
 350 ** is the week which has the majority of its days in the new year. Week 01
 351 ** might also contain days from the previous year and the week before week
 352 ** 01 of a year is the last week (52 or 53) of the previous year even if
 353 ** it contains days from the new year. A week starts with Monday (day 1)
 354 ** and ends with Sunday (day 7). For example, the first week of the year
 355 ** 1997 lasts from 1996-12-30 to 1997-01-05..."
 356 ** (ado, 1996-01-02)
 357 */
 358                                 {
 359                                         int     year;
 360                                         int     base;
 361                                         int     yday;
 362                                         int     wday;
 363                                         int     w;
 364
 365                                         year = t->tm_year;
 366                                         base = TM_YEAR_BASE;
 367                                         yday = t->tm_yday;
 368                                         wday = t->tm_wday;
 369                                         for ( ; ; ) {
 370                                                 int     len;
 371                                                 int     bot;
 372                                                 int     top;
 373
 374                                                 len = isleap_sum(year, base) ?
 375                                                         DAYSPERLYEAR :
 376                                                         DAYSPERNYEAR;
 377                                                 /*
 378                                                 ** What yday (-3 ... 3) does
 379                                                 ** the ISO year begin on?
 380                                                 */
 381                                                 bot = ((yday + 11 - wday) %
 382                                                         DAYSPERWEEK) - 3;
 383                                                 /*
 384                                                 ** What yday does the NEXT
 385                                                 ** ISO year begin on?
 386                                                 */
 387                                                 top = bot -
 388                                                         (len % DAYSPERWEEK);
 389                                                 if (top < -3)
 390                                                         top += DAYSPERWEEK;
 391                                                 top += len;
 392                                                 if (yday >= top) {
 393                                                         ++base;
 394                                                         w = 1;
 395                                                         break;
 396                                                 }
 397                                                 if (yday >= bot) {
 398                                                         w = 1 + ((yday - bot) /
 399                                                                 DAYSPERWEEK);
 400                                                         break;
 401                                                 }
 402                                                 --base;
 403                                                 yday += isleap_sum(year, base) ?
 404                                                         DAYSPERLYEAR :
 405                                                         DAYSPERNYEAR;
 406                                         }
 407 #ifdef XPG4_1994_04_09
 408                                         if ((w == 52 &&
 409                                                 t->tm_mon == TM_JANUARY) ||
 410                                                 (w == 1 &&
 411                                                 t->tm_mon == TM_DECEMBER))
 412                                                         w = 53;
 413 #endif /* defined XPG4_1994_04_09 */
 414                                         if (*format == 'V')
 415                                                 pt = _conv(w, fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex],
 416                                                         pt, ptlim);
 417                                         else if (*format == 'g') {
 418                                                 *warnp = IN_ALL;
 419                                                 pt = _yconv(year, base, 0, 1,
 420                                                         pt, ptlim);
 421                                         } else  pt = _yconv(year, base, 1, 1,
 422                                                         pt, ptlim);
 423                                 }
 424                                 continue;
 425                         case 'v':
 426                                 /*
 427                                 ** From Arnold Robbins' strftime version 3.0:
 428                                 ** "date as dd-bbb-YYYY"
 429                                 ** (ado, 1993-05-24)
 430                                 */
 431                                 pt = _fmt("%e-%b-%Y", t, pt, ptlim, warnp);
 432                                 continue;
 433                         case 'W':
 434                                 pt = _conv((t->tm_yday + DAYSPERWEEK -
 435                                         (t->tm_wday ?
 436                                         (t->tm_wday - 1) :
 437                                         (DAYSPERWEEK - 1))) / DAYSPERWEEK,
 438                                         fmt_padding[PAD_FMT_WEEKOFYEAR][PadIndex], pt, ptlim);
 439                                 continue;
 440                         case 'w':
 441                                 pt = _conv(t->tm_wday, "%d", pt, ptlim);
 442                                 continue;
 443                         case 'X':
 444                                 pt = _fmt(tptr->X_fmt, t, pt, ptlim, warnp);
 445                                 continue;
 446                         case 'x':
 447                                 {
 448                                 int     warn2 = IN_SOME;
 449
 450                                 pt = _fmt(tptr->x_fmt, t, pt, ptlim, &warn2);
 451                                 if (warn2 == IN_ALL)
 452                                         warn2 = IN_THIS;
 453                                 if (warn2 > *warnp)
 454                                         *warnp = warn2;
 455                                 }
 456                                 continue;
 457                         case 'y':
 458                                 *warnp = IN_ALL;
 459                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 0, 1,
 460                                         pt, ptlim);
 461                                 continue;
 462                         case 'Y':
 463                                 pt = _yconv(t->tm_year, TM_YEAR_BASE, 1, 1,
 464                                         pt, ptlim);
 465                                 continue;
 466                         case 'Z':
 467 #ifdef TM_ZONE
 468                                 if (t->TM_ZONE != NULL)
 469                                         pt = _add(t->TM_ZONE, pt, ptlim);
 470                                 else
 471 #endif /* defined TM_ZONE */
 472                                 if (t->tm_isdst >= 0)
 473                                         pt = _add(tzname[t->tm_isdst != 0],
 474                                                 pt, ptlim);
 475                                 /*
 476                                 ** C99 says that %Z must be replaced by the
 477                                 ** empty string if the time zone is not
 478                                 ** determinable.
 479                                 */
 480                                 continue;
 481                         case 'z':
 482                                 {
 483                                 int             diff;
 484                                 char const *    sign;
 485
 486                                 if (t->tm_isdst < 0)
 487                                         continue;
 488 #ifdef TM_GMTOFF
 489                                 diff = t->TM_GMTOFF;
 490 #else /* !defined TM_GMTOFF */
 491                                 /*
 492                                 ** C99 says that the UTC offset must
 493                                 ** be computed by looking only at
 494                                 ** tm_isdst. This requirement is
 495                                 ** incorrect, since it means the code
 496                                 ** must rely on magic (in this case
 497                                 ** altzone and timezone), and the
 498                                 ** magic might not have the correct
 499                                 ** offset. Doing things correctly is
 500                                 ** tricky and requires disobeying C99;
 501                                 ** see GNU C strftime for details.
 502                                 ** For now, punt and conform to the
 503                                 ** standard, even though it's incorrect.
 504                                 **
 505                                 ** C99 says that %z must be replaced by the
 506                                 ** empty string if the time zone is not
 507                                 ** determinable, so output nothing if the
 508                                 ** appropriate variables are not available.
 509                                 */
 510                                 if (t->tm_isdst == 0)
 511 #ifdef USG_COMPAT
 512                                         diff = -timezone;
 513 #else /* !defined USG_COMPAT */
 514                                         continue;
 515 #endif /* !defined USG_COMPAT */
 516                                 else
 517 #ifdef ALTZONE
 518                                         diff = -altzone;
 519 #else /* !defined ALTZONE */
 520                                         continue;
 521 #endif /* !defined ALTZONE */
 522 #endif /* !defined TM_GMTOFF */
 523                                 if (diff < 0) {
 524                                         sign = "-";
 525                                         diff = -diff;
 526                                 } else  sign = "+";
 527                                 pt = _add(sign, pt, ptlim);
 528                                 diff /= SECSPERMIN;
 529                                 diff = (diff / MINSPERHOUR) * 100 +
 530                                         (diff % MINSPERHOUR);
 531                                 pt = _conv(diff,
 532                                         fmt_padding[PAD_FMT_YEAR][PadIndex], pt, ptlim);
 533                                 }
 534                                 continue;
 535                         case '+':
 536                                 pt = _fmt(tptr->date_fmt, t, pt, ptlim,
 537                                         warnp);
 538                                 continue;
 539                         case '-':
 540                                 if (PadIndex != PAD_DEFAULT)
 541                                         break;
 542                                 PadIndex = PAD_LESS;
 543                                 goto label;
 544                         case '_':
 545                                 if (PadIndex != PAD_DEFAULT)
 546                                         break;
 547                                 PadIndex = PAD_SPACE;
 548                                 goto label;
 549                         case '0':
 550                                 if (PadIndex != PAD_DEFAULT)
 551                                         break;
 552                                 PadIndex = PAD_ZERO;
 553                                 goto label;
 554                         case '%':
 555                         /*
 556                         ** X311J/88-090 (4.12.3.5): if conversion char is
 557                         ** undefined, behavior is undefined. Print out the
 558                         ** character itself as printf(3) also does.
 559                         */
 560                         default:
 561                                 break;
 562                         }
 563                 }
 564                 if (pt == ptlim)
 565                         break;
 566                 *pt++ = *format;
 567         }
 568         return pt;
 569 }
 570
 571 static char *
 572 _conv(n, format, pt, ptlim)
 573 const int               n;
 574 const char * const      format;
 575 char * const            pt;
 576 const char * const      ptlim;
 577 {
 578         char    buf[INT_STRLEN_MAXIMUM(int) + 1];
 579
 580         (void) sprintf(buf, format, n);
 581         return _add(buf, pt, ptlim);
 582 }
 583
 584 static char *
 585 _add(str, pt, ptlim)
 586 const char *            str;
 587 char *                  pt;
 588 const char * const      ptlim;
 589 {
 590         while (pt < ptlim && (*pt = *str++) != '\0')
 591                 ++pt;
 592         return pt;
 593 }
 594
 595 /*
 596 ** POSIX and the C Standard are unclear or inconsistent about
 597 ** what %C and %y do if the year is negative or exceeds 9999.
 598 ** Use the convention that %C concatenated with %y yields the
 599 ** same output as %Y, and that %Y contains at least 4 bytes,
 600 ** with more only if necessary.
 601 */
 602
 603 static char *
 604 _yconv(a, b, convert_top, convert_yy, pt, ptlim)
 605 const int               a;
 606 const int               b;
 607 const int               convert_top;
 608 const int               convert_yy;
 609 char *                  pt;
 610 const char * const      ptlim;
 611 {
 612         register int    lead;
 613         register int    trail;
 614
 615 #define DIVISOR 100
 616         trail = a % DIVISOR + b % DIVISOR;
 617         lead = a / DIVISOR + b / DIVISOR + trail / DIVISOR;
 618         trail %= DIVISOR;
 619         if (trail < 0 && lead > 0) {
 620                 trail += DIVISOR;
 621                 --lead;
 622         } else if (lead < 0 && trail > 0) {
 623                 trail -= DIVISOR;
 624                 ++lead;
 625         }
 626         if (convert_top) {
 627                 if (lead == 0 && trail < 0)
 628                         pt = _add("-0", pt, ptlim);
 629                 else    pt = _conv(lead, "%02d", pt, ptlim);
 630         }
 631         if (convert_yy)
 632                 pt = _conv(((trail < 0) ? -trail : trail), "%02d", pt, ptlim);
 633         return pt;
 634 }