On Jul 10, 1:35 pm, MRAB <[EMAIL PROTECTED]> wrote:
> On Jul 10, 4:56 am, Jordan <[EMAIL PROTECTED]> wrote:
>
>
>
> > I am trying to rewrite some C source code for a poker hand evaluator
> > in Python. Putting aside all of the comments such as just using the C
> > code, or using SWIG, etc. I have been having problems with my Python
> > code not responding the same way as the C version.
>
> > C verison:
>
> > unsigned find_fast(unsigned u)
> > {
> > unsigned a, b, r;
> > u += 0xe91aaa35;
> > u ^= u >> 16;
> > u += u << 8;
> > u ^= u >> 4;
> > b = (u >> 8) & 0x1ff;
> > a = (u + (u << 2)) >> 19;
> > r = a ^ hash_adjust[b];
> > return r;
>
> > }
>
> > my version (Python, hopefully ;)):
>
> > def find_fast(u):
> > u += 0xe91aaa35
> > u ^= u >> 16
> > u += u << 8
> > u ^= u >> 4
> > b = (u >> 8) & 0x1ff
> > a = (u + (u << 2)) >> 19
> > r = a ^ hash_adjust[b]
> > return r
>
> > As far as I understand the unsigned instructions in C just increase
> > amount of bytes the int can hold, and Python automatically converts to
> > longs which have infinite size when necessary, so I am not sure why I
> > am getting different results.
>
> > I assume that I am missing something fairly simple here, so help a
> > n00b out if you can :)
>
> > Thanks in advance,
>
> > jnb
>
> You want to restrict the values to 32 bits. The result of + or << may
> exceed 32 bits, so you need to mask off the excess bits afterwards.
>
> def find_fast(u):
> mask = 0xffffffff
> u = (u + 0xe91aaa35) & mask
> u ^= u >> 16
> u = (u + (u << 8)) & mask # can get away with only 1 mask here
> u ^= u >> 4
> b = (u >> 8) & 0x1ff
> a = ((u + (u << 2)) & mask) >> 19 # can get away with only 1 mask
> here
> r = a ^ hash_adjust[b]
> return r
>
> HTH
Well, I guess there are two problems....the masking and the fact the
in C it seems to for some reason overflow and become a negative
value....still not sure why it does it....So the code with just
masking doesn't work, you still need some sort of weird inversion like
the ~(0xFFFFFFFF - u).....weird
anyone?
haha
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