SQLite

      zBuf[0] = '-';
      sqlite3_result_text(context, zBuf, 11, SQLITE_TRANSIENT);
    }else{
      sqlite3_result_text(context, &zBuf[1], 10, SQLITE_TRANSIENT);
    }
  }
}

/*
** Compute the one-based day of the year for the DateTime pDate.
** Jan01 = 1,  Jan02 = 2, ... Dec31 = 356 or 366.
*/
static int dayOfYear(DateTime *pDate){
  DateTime jan01 = *pDate;
  assert( jan01.validYMD );
  assert( jan01.validHMS );
  assert( pDate->validJD );
  jan01.validJD = 0;
  jan01.M = 1;
  jan01.D = 1;
  computeJD(&jan01);
  return (int)((pDate->iJD-jan01.iJD+45300000)/86400000) + 1;
}

/*
** Return the day of the week.  1==Monday, 2=Tues, ..., 7=Sunday.
*/
static int dayOfWeek(DateTime *pDate){
  int w;
  assert( pDate->validJD );
  w = ((pDate->iJD+129600000)/86400000) % 7;
  if( w==0 ) w = 7;
  return w;
}

/*
** Compute the day-of-week (0=Sunday, 1=Monday, ..., 6=Saturday) for
** the last day of the calendar year Y.
*/
static int lastDayOfYear(int Y){
  return (Y + (Y/4) - (Y/100) + (Y/400))%7;
}

/*
** Return the number of ISO weeks in calendar year Y.  The answer is
** either 52 or 53.
*/
static int weeksInYear(int Y){
  if( lastDayOfYear(Y)==4 || lastDayOfYear(Y-1)==3 ){
    return 53;
  }else{
    return 52;
  }
}

/*
** Compute the number days since the start of the ISO-week year for pDate.
** The ISO-week year starts on the first day of the week (always a Monday)
** that contains the first Thursday on or after January 1.
*/
static int isoWeekNumber(DateTime *pDate){
  int wn = (10 + dayOfYear(pDate) - dayOfWeek(pDate))/7;
  if( wn<1 ){
    wn = weeksInYear(pDate->Y-1);
  }else if( wn>weeksInYear(pDate->Y) ){
    wn = 1;
  }
  return wn;
}

/*
**    strftime( FORMAT, TIMESTRING, MOD, MOD, ...)
**
** Return a string described by FORMAT.  Conversions as follows:
**
**   %d  day of month  01-31
**   %e  day of month  1-31
**   %f  ** fractional seconds  SS.SSS
**   %F  ISO date.  YYYY-MM-DD
**   %G  ISO year corresponding to %V 0000-9999.
**   %g  2-digit ISO year corresponding to %V 00-99
**   %H  hour 00-24
**   %k  hour  0-24  (leading zero converted to space)
**   %I  hour 01-12
**   %j  day of year 001-366
**   %J  ** julian day number
**   %l  hour  1-12  (leading zero converted to space)
**   %m  month 01-12
**   %M  minute 00-59
**   %p  "am" or "pm"
**   %P  "AM" or "PM"
**   %R  time as HH:MM
**   %s  seconds since 1970-01-01
**   %S  seconds 00-59
**   %T  time as HH:MM:SS
**   %u  day of week 1-7  Monday==1, Sunday==7
**   %w  day of week 0-6  Sunday==0, Monday==1
**   %U  week of year 00-53  (First Sunday is start of week 01)
**   %V  week of year 01-53  (First week containing Thursday is week 01)
**   %W  week of year 00-53  (First Monday is start of week 01)
**   %Y  year 0000-9999
**   %%  %
*/
static void strftimeFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv

    cf = zFmt[i];
    switch( cf ){
      case 'd':  /* Fall thru */
      case 'e': {
        sqlite3_str_appendf(&sRes, cf=='d' ? "%02d" : "%2d", x.D);
        break;
      }
      case 'f': {  /* Fractional seconds.  (Non-standard) */
        double s = x.s;
        if( s>59.999 ) s = 59.999;
        sqlite3_str_appendf(&sRes, "%06.3f", s);
        break;
      }
      case 'F': {
        sqlite3_str_appendf(&sRes, "%04d-%02d-%02d", x.Y, x.M, x.D);
        break;
      }
      case 'G': /* Fall thru */
      case 'g': {
        int Y = x.Y;
        if( x.M==12 && isoWeekNumber(&x)==1 ){
          Y++;
        }else if( x.M==1 && isoWeekNumber(&x)>=52 ){
          Y--;
        }
        if( cf=='g' ){
          sqlite3_str_appendf(&sRes, "%02d", Y%100);
        }else{
          sqlite3_str_appendf(&sRes, "%04d", Y);
        }
        break;
      }
      case 'H':
      case 'k': {
        sqlite3_str_appendf(&sRes, cf=='H' ? "%02d" : "%2d", x.h);
        break;
      }
      case 'I': /* Fall thru */
      case 'l': {
        int h = x.h;
        if( h>12 ) h -= 12;
        if( h==0 ) h = 12;
        sqlite3_str_appendf(&sRes, cf=='I' ? "%02d" : "%2d", h);
        break;
      }

      case 'j': {  /* Day of year.  Jan01==1, Jan02==2, and so forth */

        int nDay = dayOfYear(&x);








        sqlite3_str_appendf(&sRes,"%03d",nDay);



        break;
      }
      case 'J': {  /* Julian day number.  (Non-standard) */
        sqlite3_str_appendf(&sRes,"%.16g",x.iJD/86400000.0);
        break;
      }
      case 'm': {
        sqlite3_str_appendf(&sRes,"%02d",x.M);
        break;
      }

        sqlite3_str_appendf(&sRes,"%02d",(int)x.s);
        break;
      }
      case 'T': {
        sqlite3_str_appendf(&sRes,"%02d:%02d:%02d", x.h, x.m, (int)x.s);
        break;
      }
      case 'u':    /* Day of week.  1 to 7.  Monday==1, Sunday==7 */
      case 'w': {  /* Day of week.  0 to 6.  Sunday==0, Monday==1 */
        char c = (char)(((x.iJD+129600000)/86400000) % 7) + '0';
        if( c=='0' && cf=='u' ) c = '7';
        sqlite3_str_appendchar(&sRes, 1, c);
        break;
      }
      case 'U': {  /* Week num. 00-53. First Sun of the year is week 01 */
        int wd;    /* 0=Sunday, 1=Monday, 2=Tuesday, ... 7=Saturday */
        int nDay;  /* Day of the year.  0..364 or 0..365 for leapyears */
        nDay = dayOfYear(&x);
        wd = (int)(((x.iJD+43200000)/86400000 + 1)%7);
        sqlite3_str_appendf(&sRes,"%02d",(nDay+6-wd)/7);
        break;
      }
      case 'V': {  /* Week num. 01-53. First week with a Thur is week 01 */
        sqlite3_str_appendf(&sRes,"%02d", isoWeekNumber(&x));
        break;
      }
      case 'W': {  /* Week num. 00-53. First Mon of the year is week 01 */
        int wd;    /* 0=Monday, 1=Tuesday, ... 6=Sunday */
        int nDay;  /* Day of the year.  0..364 or 0..365 for leapyears */
        nDay = dayOfYear(&x);
        wd = (int)(((x.iJD+43200000)/86400000)%7);
        sqlite3_str_appendf(&sRes,"%02d",(nDay+6-wd)/7);
        break;
      }
      case 'Y': {
        sqlite3_str_appendf(&sRes,"%04d",x.Y);
        break;
      }
      case '%': {
        sqlite3_str_appendchar(&sRes, 1, '%');

  }
  return $x
}
datetest 3.16 "strftime('[repeat 200 %Y]','2003-10-31')" [repeat 200 2003]
datetest 3.17 "strftime('[repeat 200 abc%m123]','2003-10-31')" \
    [repeat 200 abc10123]

foreach c {a b c h i n o q r t v x y z
           A B C D E K L N O Q Z
           0 1 2 3 4 5 6 6 7 9 _} {
  datetest 3.18.$c "strftime('%$c','2003-10-31')" NULL
}
datetest 3.20 {strftime('%e','2023-08-09')} { 9}
datetest 3.21 {strftime('%F %T','2023-08-09 01:23')} {2023-08-09 01:23:00}
datetest 3.22 {strftime('%k','2023-08-09 04:59:59')} { 4}
datetest 3.23 {strftime('%I%P','2023-08-09 11:59:59')} {11am}

#
ifcapable {!datetime} {
  finish_test
  return
}

if {$tcl_platform(os)=="Linux"} {
  set FMT {%d,%e,%F,%H,%k,%I,%l,%j,%m,%M,%u,%w,%W,%Y,%%,%P,%p,%U,%V,%G,%g}
} else {
  set FMT {%d,%e,%F,%H,%I,%j,%p,%R,%u,%w,%W,%%}
}
for {set i 0} {$i<=24854} {incr i} {
  set TS [expr {$i*86401}]
  do_execsql_test date4-$i {
    SELECT strftime($::FMT,$::TS,'unixepoch');