Revert "fix, use AC_CHECK_PROG instead of AM_MISSING_PROG for gperf support"

This reverts commit 315727ac0f68500332cc4bf92fac82c93c02f03e.
fix, use AC_PATH_PROG instead of AM_MISSING_PROG because the latter ...

... always defines GPERF which makes the conditional test -n ... always true

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
chore, declare variable GPERF precious

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'bld/chn'

* bld/chn:
  chore, declare variable GPERF precious
  fix, use AC_PATH_PROG instead of AM_MISSING_PROG because the latter ...
  Revert "fix, use AC_CHECK_PROG instead of AM_MISSING_PROG for gperf support"
fix, use __daisy_get_year() in __daisy_to_ywd() to get a year estimate

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, provide full and 28y version of __get_z31wk()

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
cosmetics, put TO_BASE and TO_YEAR definitions upfront

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
cosmetics, comment guards

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, actually use the correct linear form for the 28y cycle in __get_cumwk()

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, use same fix-up in __daisy_to_ywd() as __make_ywd() employs to correct for hanging weeks

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/conv' into next

* core/conv:
  fix, use same fix-up in __daisy_to_ywd() as __make_ywd() employs to correct for hanging weeks
  fix, actually use the correct linear form for the 28y cycle in __get_cumwk()
  cosmetics, comment guards
  cosmetics, put TO_BASE and TO_YEAR definitions upfront
  minor, provide full and 28y version of __get_z31wk()
  fix, use __daisy_get_year() in __daisy_to_ywd() to get a year estimate
minor, provide ywd->ymcw and ymcw->ywd converter

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
test, provide regression for ymcw->abscnt

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
test, bring regressions for ymcw<->ywd conversion

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
fix, produce proper year counts for ymcw dates upon %C

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
minor, rewrite __ymcw_get_yday() using a lookup table and accounting for ...

... the difference between the current weekday and F01-weekday.

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'core/conv' into next

* core/conv:
  minor, rewrite __ymcw_get_yday() using a lookup table and accounting for ...
  fix, produce proper year counts for ymcw dates upon %C
  test, bring regressions for ymcw<->ywd conversion
  test, provide regression for ymcw->abscnt
  minor, provide ywd->ymcw and ymcw->ywd converter
Merge branch 'next'

* next: (34 commits)
  minor, rewrite __ymcw_get_yday() using a lookup table and accounting for ...
  fix, produce proper year counts for ymcw dates upon %C
  test, bring regressions for ymcw<->ywd conversion
  test, provide regression for ymcw->abscnt
  minor, provide ywd->ymcw and ymcw->ywd converter
  fix, use same fix-up in __daisy_to_ywd() as __make_ywd() employs to correct for hanging weeks
  fix, actually use the correct linear form for the 28y cycle in __get_cumwk()
  cosmetics, comment guards
  cosmetics, put TO_BASE and TO_YEAR definitions upfront
  minor, provide full and 28y version of __get_z31wk()
  fix, use __daisy_get_year() in __daisy_to_ywd() to get a year estimate
  fix, perform another cycle in __daisy_get_year() (of the former for-loop)
  fix, PEBKAC, don't use ymcw->ywd converter (committed accidentally)
  minor, introduce 28y cycle in ywd's __get_isowk()
  chore, cosmetics, rid __daisy_get_year() of the for-loop
  minor, provide __daisy_to_ywd() converter using a 28y cycle for the cumulative weeks since 1917
  fix, correctly convert from ywd to ymd, provide __get_z31wk() and __ywd_get_dec31_wday()
  fix, adapt __daisy_feasible_p() disallowing durations denoted in years
  fix, offset by 2001 years in __jan00_daisy() to capture the leap mechanism of years 2100, 2200 and 2300
  test, adapt basic_get_jan01_wday regression to recent fix
  ...