OpenEuphoria

Re: fast bit rotation

• Posted by Tommy Carlier <tommy.carlier at pandora.be> Dec 31, 2003
• 432 views

------- <code>
include machine.e

constant rotate_left = allocate(15), rotate_left_param = rotate_left + 2
poke(rotate_left, {
     #60,                    --    0: pusha
     #B8,#00,#00,#00,#00,    --    1: mov eax, dword param (2)
     #D1,#C0,                --    6: rol eax, 1
     #A3,#6A,#0A,#82,#82,    --    8: mov [@param], eax
     #61,                    --    D: popa
     #C3})                   --    E: ret
poke4(rotate_left + 9, rotate_left_param) -- @param

constant rotate_right = allocate(15), rotate_right_param = rotate_right + 2
poke(rotate_right, {
     #60,                    --    0: pusha
     #B8,#00,#00,#00,#00,    --    1: mov eax, dword param (2)
     #D1,#C8,                --    6: ror eax, 1
     #A3,#6A,#3A,#C2,#83,    --    8: mov [@param], eax
     #61,                    --    D: popa
     #C3})                   --    E: ret
poke4(rotate_right + 9, rotate_right_param) -- @param

-- To use:
poke4(rotate_left_param, i) -- i = an integer
call(rotate_left)
i = peek4s(rotate_left_param)

poke4(rotate_right_param, j) -- j = an integer
call(rotate_right)
j = peek4s(rotate_right_param)

-- Before closing your program, you should call:
free(rotate_left)
free(rotate_right)
------- </code>

Perhaps there are faster methods than this, but on my laptop (Pentium II 
433MHz, 64MB RAM), I can do 10_000_000 (ten million) rotations in 19.11 
seconds, which is more than 500_000 rotations per second.
-- 

Tommy Carlier
tommy online: http://users.pandora.be/tommycarlier