OpenEuphoria

RE: poke - peek Speed?

• Posted by Don Phillips <EuNexus at yahoo.com> Nov 13, 2002
• 566 views

::CODE SNIP::

> I will use it to write to a file values less than 32768 in byte format. 
> That
> is why I use integer and not atom arguments.
> Why does the poke - peek version take more time than the other, that 
> uses
> division? Using allocate_low instead of allocate, it even takes more 
> time!
> TIA.

Is your algorithm for to2bytes correct?  Looking into machine.e I see 
the fuction int_to_bytes is declared as:

global function int_to_bytes(atom x)
-- returns value of x as a sequence of 4 bytes 
-- that you can poke into memory 
--      {bits 0-7,  (least significant)
--       bits 8-15,
--       bits 16-23,
--       bits 24-31} (most significant)
-- This is the order of bytes in memory on 386+ machines.
    integer a,b,c,d
    
    a = remainder(x, #100)
    x = floor(x / #100)
    b = remainder(x, #100)
    x = floor(x / #100)
    c = remainder(x, #100)
    x = floor(x / #100)
    d = remainder(x, #100)
    return {a,b,c,d}
end function

You will notice it returns >>> {a,b,c,d} so the first two bytes would be

a = remainder(x, #100)
x = floor(x / #100)
b = remainder(x, #100)

However your version written as:

function to2bytes(integer u)
     return and_bits(u, #FF) & floor(u / 256)
end function

Only does the a and x calculation... what happened to b?
If I am correct and your algorithm is slightly off, that will explain 
the speed difference.

Don