-- gb: 前側の和文文字 b 由来の glue/kern (maybe nil)
-- ga: 後側の和文文字 a 由来の glue/kern (maybe nil)
-- 両者から，b と a の間に入る glue/kern を計算する

function ltj.calc_between_two_jchar_aux_large(gb,ga)
   if not gb then 
      return ga
   else
      if not ga then return gb end
      local k = node.type(gb.id) .. node.type(ga.id)
      if k == 'glueglue' then 
	 -- 両方とも glue．大きい方をとる
	 gb.spec.width   = math.max(gb.spec.width,ga.spec.width)
	 gb.spec.stretch = math.max(gb.spec.stretch,ga.spec.shrink)
	 gb.spec.shrink  = math.min(gb.spec.shrink,ga.spec.shrink)
	 return gb
      elseif k == 'kernkern' then
	 -- 両方とも kern．
	 gb.kern = math.max(gb.kern,ga.kern)
	 return gb
      elseif k == 'kernglue' then 
	 -- gb: kern, ga: glue
	 ga.spec.width   = math.max(gb.kern,ga.spec.width)
	 ga.spec.stretch = math.max(ga.spec.stretch,0)
	 ga.spec.shrink  = math.min(ga.spec.shrink,0)
	 return ga
      else
	 -- gb: glue, ga: kern
	 gb.spec.width   = math.max(ga.kern,gb.spec.width)
	 gb.spec.stretch = math.max(gb.spec.stretch,0)
	 gb.spec.shrink  = math.min(gb.spec.shrink,0)
	 return gb
      end
   end
end
function ltj.calc_between_two_jchar_aux_small(gb,ga)
   if not gb then 
      return ga
   else
      if not ga then return gb end
      local k = node.type(gb.id) .. node.type(ga.id)
      if k == 'glueglue' then 
	 -- 両方とも glue．大きい方をとる
	 gb.spec.width   = math.min(gb.spec.width,ga.spec.width)
	 gb.spec.stretch = math.min(gb.spec.stretch,ga.spec.shrink)
	 gb.spec.shrink  = math.max(gb.spec.shrink,ga.spec.shrink)
	 return gb
      elseif k == 'kernkern' then
	 -- 両方とも kern．
	 gb.kern = math.min(gb.kern,ga.kern)
	 return gb
      elseif k == 'kernglue' then 
	 -- gb: kern, ga: glue
	 ga.spec.width   = math.min(gb.kern,ga.spec.width)
	 ga.spec.stretch = math.min(ga.spec.stretch,0)
	 ga.spec.shrink  = math.max(ga.spec.shrink,0)
	 return ga
      else
	 -- gb: glue, ga: kern
	 gb.spec.width   = math.min(ga.kern,gb.spec.width)
	 gb.spec.stretch = math.min(gb.spec.stretch,0)
	 gb.spec.shrink  = math.max(gb.spec.shrink,0)
	 return gb
      end
   end
end
function ltj.calc_between_two_jchar_aux_average(gb,ga)
   if not gb then 
      return ga
   else
      if not ga then return gb end
      local k = node.type(gb.id) .. node.type(ga.id)
      if k == 'glueglue' then 
	 -- 両方とも glue．平均をとる
	 gb.spec.width   = tex.round((gb.spec.width+ga.spec.width)/2)
	 gb.spec.stretch = tex.round((gb.spec.stretch+ga.spec.shrink)/2)
	 gb.spec.shrink  = tex.round((gb.spec.shrink+ga.spec.shrink)/2)
	 return gb
      elseif k == 'kernkern' then
	 -- 両方とも kern．平均をとる
	 gb.kern = tex.round((gb.kern+ga.kern)/2)
	 return gb
      elseif k == 'kernglue' then 
	 -- gb: kern, ga: glue
	 ga.spec.width   = tex.round((gb.kern+ga.spec.width)/2)
	 ga.spec.stretch = tex.round(ga.spec.stretch/2)
	 ga.spec.shrink  = tex.round(ga.spec.shrink/2)
	 return ga
      else
	 -- gb: glue, ga: kern
	 gb.spec.width   = tex.round((ga.kern+gb.spec.width)/2)
	 gb.spec.stretch = tex.round(gb.spec.stretch/2)
	 gb.spec.shrink  = tex.round(gb.spec.shrink/2)
	 return gb
      end
   end
end
function ltj.calc_between_two_jchar_aux_both(gb,ga)
   if not gb then 
      return ga
   else
      if not ga then return gb end
      local k = node.type(gb.id) .. node.type(ga.id)
      if k == 'glueglue' then 
	 gb.spec.width   = tex.round((gb.spec.width+ga.spec.width))
	 gb.spec.stretch = tex.round((gb.spec.stretch+ga.spec.shrink))
	 gb.spec.shrink  = tex.round((gb.spec.shrink+ga.spec.shrink))
	 return gb
      elseif k == 'kernkern' then
	 gb.kern = tex.round((gb.kern+ga.kern))
	 return gb
      elseif k == 'kernglue' then 
	 -- gb: kern, ga: glue
	 ga.spec.width   = tex.round((gb.kern+ga.spec.width))
	 return ga
      else
	 -- gb: glue, ga: kern
	 gb.spec.width   = tex.round((ga.kern+gb.spec.width))
	 return gb
      end
   end
end

ltj.calc_between_two_jchar_aux=ltj.calc_between_two_jchar_aux_average