with input (hexstr) as
(select '12345EA' from sysibm.sysdummy1
)
,
hex2dbl(hexstr, hexrmd, dblnmbr) as
(
select hexstr, ucase(hexstr), double(0.) 
from input 
union all 
select hexstr, substr(hexrmd, 2) , 
dblnmbr + 
power(16, length(hexrmd) - 1) * 

case when substr(hexrmd, 1, 1) between '0' and '9' 
then double(substr(hexrmd, 1, 1)) 
when substr(hexrmd, 1, 1) = 'A' then 10.
when substr(hexrmd, 1, 1) = 'B' then 11.
when substr(hexrmd, 1, 1) = 'C' then 12.
when substr(hexrmd, 1, 1) = 'D' then 13.
when substr(hexrmd, 1, 1) = 'E' then 14.
when substr(hexrmd, 1, 1) = 'F' then 15.
else  nullif(0, 0)
end

from   hex2dbl
where  length(hexrmd) >= 1
)
,
hex2int(hexstr, intfromhex) as
(select hexstr,
case
when dblnmbr <= 2147483647 then int(dblnmbr) 
else int(dblnmbr - 2 * 2147483648) 
end 
from hex2dbl 
where length(hexrmd) = 0
) 
select * from hex2int

with input (hexstr) as
(select '12345EA' from sysibm.sysdummy1
)
,
hex2dbl(hexstr, hexrmd, dblnmbr) as
(
select hexstr, ucase(hexstr), double(0.) 
from input 

union all 

select hexstr, substr(hexrmd, 2) , 
dblnmbr + 
power(16, length(hexrmd) - 1) * 
case Locate(substr(hexrmd, 1, 1), '0123456789ABCDEF')
when 0 then nullif(0, 0)
else Locate(substr(hexrmd, 1, 1), '0123456789ABCDEF') - 1 
end
  from  hex2dbl
where  length(hexrmd) >= 1
)
,
hex2int(hexstr, intfromhex) as
(select hexstr,
case
when dblnmbr <= 2147483647 then int(dblnmbr) 
else int(dblnmbr - 2 * 2147483648) 
end 
from hex2dbl 
where length(hexrmd) = 0
)
 select * from hex2int

with input(intnmbr) as
(select int(2009911) from sysibm.sysdummy1
)
,
int2hex (intnmbr, remdbl, hexstr) as
(
select 
intnmbr, 
int(case when intnmbr >= 0  then intnmbr
         else intnmbr + 2 * 2147483648 
    end),
varchar('', 100)
from input   

union all
select 
intnmbr, int(remdbl / 16),
case  when mod(remdbl, 16) between 0 and 9 
                                 then varchar(mod(remdbl, 16)) 
      when mod(remdbl, 16) = 10 then 'A'
      when mod(remdbl, 16) = 11 then 'B' 
      when mod(remdbl, 16) = 12 then 'C' 
      when mod(remdbl, 16) = 13 then 'D' 
      when mod(remdbl, 16) = 14 then 'E'  
      when mod(remdbl, 16) = 15 then 'F' 
end || hexstr
from int2hex 
where remdbl > 16

union all
select 
intnmbr, nullif(0, 0),
case  when int(remdbl) between 0 and 9 
                                 then varchar(int(remdbl))
      when int(remdbl) = 10 then 'A'
      when int(remdbl) = 11 then 'B' 
      when int(remdbl) = 12 then 'C' 
      when int(remdbl) = 13 then 'D' 
      when int(remdbl) = 14 then 'E'  
      when int(remdbl) = 15 then 'F' 
end || hexstr 
from int2hex 
where remdbl < 16 

) 
select  intnmbr, hexstr 
  from  int2hex
  where remdbl is null