declare 
--  x number := 10+16+32+100043435;
  x number := 170141183460469231731687303715884105727;
  y integer;
  function r(x integer, n number:=1) return integer is
     offs integer := power(2,n);
     x2 integer := trunc(x - bitand(x, x/offs)+ trunc(x/offs));
  begin
    if n < 7 and x2 <> x then return r(x2,n+1); 
    else return x2;
    end if;
  end;
begin 
  y := r(x/2)+1;
  dbms_output.put_line('Игого: '||y||' (0x'||to_char(y,'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')||')');
end;
/

SQL> 
with s0 as
 (select power(2,127) x from dual
 union all select 258 from dual
 union all select 1 from dual
 union all select 0 from dual
 union all select abs(dbms_random.value(1,170141183460469231731687303715)) from dual
 union all select abs(dbms_random.value(1,170141183460469231731687303715884105727)) from dual
 union all select 170141183460469231731687303715884105727 from dual
 )
, s1 as  (select x, bitand(-x/2-1, -x/4-1) y from s0)
, s2 as  (select x, bitand(y, y/4 - 1) y from s1)
, s8 as  (select x, bitand(y, y/16 - 1) y from s2)
, s16 as (select x, bitand(y, y/256 - 1) y from s8)
, s32 as (select x, bitand(y, y/65536 - 1) y from s16)
, s64 as (select x, bitand(y, y/4294967296 - 1) y from s32)
, s128 as(select x, -(bitand(y, y/18446744073709551616 - 1)) y from s64)
select to_char(x,'fm9999999999999999999999999999999999999999') X_Dec
     , '0x'||to_char(x, 'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')  X_Hex
     , to_char(y,'fm9999999999999999999999999999999999999999') MSB_Dec
     , '0x'||to_char(y, 'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')  MSB_Hex
     , log(2,y) Msb_pos
from s128
;
 
X_DEC                                     X_HEX                               MSB_DEC                                   MSB_HEX                                MSB_POS
----------------------------------------- ----------------------------------- ----------------------------------------- ----------------------------------- ----------
170141183460469231731687303715884105728   0x80000000000000000000000000000000  170141183460469231731687303715884105728   0x80000000000000000000000000000000         127
258                                       0x102                               256                                       0x100                                        8
1                                         0x1                                 1                                         0x1                                          0
0                                         0x0                                 1                                         0x1                                          0
133443245482288878540034551612            0x1af2daa60c54cd8f9c6662f3c         79228162514264337593543950336             0x1000000000000000000000000                 96
119211094692360684699054379122744794223   0x59af38c12477e5bcb50f833e0ff29c6f  85070591730234615865843651857942052864    0x40000000000000000000000000000000         126
170141183460469231731687303715884105727   0x7fffffffffffffffffffffffffffffff  85070591730234615865843651857942052864    0x40000000000000000000000000000000         126
 
7 rows selected
 
SQL> 

with s0 as
 (select power(2,127) x from dual
 union all select 258 from dual
 union all select 1 from dual
 union all select 0 from dual
 union all select abs(dbms_random.value(1,170141183460469231731687303715)) from dual
 union all select abs(dbms_random.value(1,170141183460469231731687303715884105727)) from dual
 union all select 170141183460469231731687303715884105727 from dual
 )
, powers as  (select power(2,level-1) msb, level-1 msb_pos from dual connect by level < 129)
select to_char(x,'fm9999999999999999999999999999999999999999') X_Dec
     , '0x'||to_char(x, 'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')  X_Hex
     , to_char(y,'fm9999999999999999999999999999999999999999') MSB_Dec
     , '0x'||to_char(y, 'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')  MSB_Hex
     , Msb_pos
from s0
   , lateral(-- закос под трюк "поиск максимума, не превосходящего N", на этом форуме впервые продемонстрированый коллегой Elic лет... много тому :)
            select msb y, msb_pos from powers where msb<x+1 order by msb desc fetch first 1 row only)
;
 
X_DEC                                     X_HEX                               MSB_DEC                                   MSB_HEX                                MSB_POS
----------------------------------------- ----------------------------------- ----------------------------------------- ----------------------------------- ----------
170141183460469231731687303715884105728   0x80000000000000000000000000000000  170141183460469231731687303715884105728   0x80000000000000000000000000000000         127
258                                       0x102                               256                                       0x100                                        8
1                                         0x1                                 1                                         0x1                                          0
47086713355477066368238054730             0x98253765c2b19b926e696d4a          39614081257132168796771975168             0x800000000000000000000000                  95
108485719561466938268229125408222236127   0x519d96eefd2e32e8825ed710730a4ddf  85070591730234615865843651857942052864    0x40000000000000000000000000000000         126
170141183460469231731687303715884105727   0x7fffffffffffffffffffffffffffffff  85070591730234615865843651857942052864    0x40000000000000000000000000000000         126
 
6 rows selected
 
SQL> 

declare
x number := 0;  
y number;  
  -- Это разместить на уровне пакета
  type t is table of number index by pls_integer;
  powers t;
  magics t;
  procedure init_powers is
  begin
    for i in 0..30 loop
      powers(power(2,i)-1) := i;
    end loop;
    magics(1) := power(2,120);
    magics(2) := power(2,90);
    magics(3) := power(2,60);
    magics(4) := power(2,30);
    magics(5) := power(2,0);
  end;
  function get_msb(x number) return number is
    lx binary_integer;
    lpow binary_integer;
  begin
    -- Инициализацию можно разместить в секции инициализации пакета
    if powers.count = 0 then init_powers; end if;
    if x <=0 then return 0; end if;
    for i in 1..5 loop
      lx := trunc(x/magics(i));
      lpow := i;
    exit when lx > 0; 
    end loop;
    return (powers.prior(lx)+1)*magics(lpow);
  end;
begin
  for i in 0..128 loop
--    x := power(2,i);
    x := x+power(2,i);
    dbms_output.put_line('    X: '||' (0x'||to_char(x,'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')||')');
    y := get_msb(x);
    dbms_output.put_line('Игого: '||' (0x'||to_char(y,'fmxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')||')');
  end loop;  
end;
/