1. RE: 32-bit operations
> -----Original Message-----
> From: Juergen Luethje [mailto:j.lue at gmx.de]
> Subject: Re: 32-bit operations
>
>
>
> Derek wrote:
>
> > Hi all,
> > it turns out that I can't use Juergen's routines after all.
> I need to do
> > arithetic that can have temporary values that extend beyond
> Euphoria's
> > 30-bit integer limit. Thanks to being reminded about the
> bits_to_int() and
> > int_to_bits() routines, I've come up with this little
> function that gives me
> > the correct values now. It seems to run fast enough for my uses too!
> >
> > global function ClipBits(atom pValue)
> > if pValue > #FFFFFFFF or pValue < 0 then
> > pValue = bits_to_int(int_to_bits(pValue,32))
> > end if
> > return pValue
> > end function
>
> My routines in 'bit.e' should handle any 32-bit signed or unsigned
> integer.
Agreed, however I still have to use an ATOM to hold a 32-bit integer.
Euphoria's INTEGER doesn't work with more than 30 bits.
> They were not designed to handle values > #FFFFFFFF, that are
> beyond the 32-bit limit. The Euphoria wrapper functions use
> user defined types, to catch those "oversized" parameters.
That's my problem. For example, I've adding two 32-bit integers and I need
to ignore overflow. Sure I can add two atoms together, but when I use you
routines (eg. shift_left(x,0)) to strip off the overflow, I get a type-check
error.
I guess if you could include some addition and subtraction routines that
ignore overflow/underflow situations, that would help.
>
> But the machine functions themselves seem to clip the parameters, like
> you want. Using the following test program, I wasn't able to
> generate an
> error. What is/are the error/s that you get with 'bit.e', Derek?
Type check errors. For example ...
c:\dparnell\win32lib\include\bit.e:105 in function shift_left()
type_check failure, a is -3141312130
and ...
c:\dparnell\win32lib\include\bit.e:105 in function shift_left()
type_check failure, a is 6010708479
But that's because I am using the function wrappers you supplied, and they
do type checking on the parameters. When I use the c_func(SHIFT_LEFT,{...})
method it works fine.
[snip]
I now use this ...
global function TEA_encypher(atom y, atom z, atom k1, atom k2, atom sum)
-- The input parameters are all 32-bit unsigned integers.
-- I return a 32-bit unsigned integer
-- The seperate assignments are there to ensure that I
-- don't lose any precision by simulating 32-bit UINTs
-- with atoms.
y = c_func(SHIFT_LEFT,{y + c_func(SHIFT_LEFT,{z,4}), 0})
y = c_func(SHIFT_LEFT,{y + xor_bits(k1, z), 0})
y = c_func(SHIFT_LEFT,{y + xor_bits(sum, c_func(SHIFT_RIGHT,{z,5})),0})
y = c_func(SHIFT_LEFT,{y + k2, 0})
return y
end function
Though if we had a 32-bit add I could do this instead...
global function TEA_encypher(atom y, atom z, atom k1, atom k2, atom sum)
-- The input parameters are all 32-bit unsigned integers.
-- I return a 32-bit unsigned integer
-- The seperate assignments are there to ensure that I
-- don't lose any precision by simulating 32-bit UINTs
-- with atoms.
y = c_func(ADD32,{y, c_func(SHIFT_LEFT,{z,4})})
y = c_func(ADD32,{y, xor_bits(k1, z)})
y = c_func(ADD32,{y, xor_bits(sum, c_func(SHIFT_RIGHT,{z,5}))})
y = c_func(ADD32,{y, k2})
return y
end function
Thanks for the help.
--
Derek
