what's the best hash function?

Discussion in 'C Programming' started by vietor.liu, Nov 25, 2005.

  1. vietor.liu

    vietor.liu Guest

    is this?

    int hashpjw(char* str,int size)
    {
    unsigned long h=0,g;
    for(unsigned char *p=(unsigned char*)str;*p;++p)
    {
    h=(h<<4)+*p;
    if(g=(h&0xf0000000))
    {
    h^=(g>>24);
    h^=g;
    }
    }
    return h%size;
    }
     
    vietor.liu, Nov 25, 2005
    #1
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  2. Re: what's the best hash function?

    "vietor.liu" <> writes:

    >is this?


    >int hashpjw(char* str,int size)
    >{
    > unsigned long h=0,g;
    > for(unsigned char *p=(unsigned char*)str;*p;++p)
    > {
    > h=(h<<4)+*p;
    > if(g=(h&0xf0000000))
    > {
    > h^=(g>>24);
    > h^=g;
    > }
    > }
    > return h%size;
    >}



    <OT>
    The answer totally depends on the type and range of inputs,
    and the purpose of the hash result. Read onwards:

    http://burtleburtle.net/bob/hash/evahash.html
    </OT>

    --
    Chris.
     
    Chris McDonald, Nov 25, 2005
    #2
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  3. vietor.liu

    Jack Klein Guest

    On Fri, 25 Nov 2005 10:21:54 +0800, "vietor.liu"
    <> wrote in comp.lang.c:

    Define "best".

    > is this?
    >
    > int hashpjw(char* str,int size)
    > {
    > unsigned long h=0,g;
    > for(unsigned char *p=(unsigned char*)str;*p;++p)
    > {
    > h=(h<<4)+*p;
    > if(g=(h&0xf0000000))
    > {
    > h^=(g>>24);
    > h^=g;
    > }
    > }
    > return h%size;
    > }
    >


    If you want to know the "best" hashing algorithm, ask in
    news:comp.programming. And supply a definition of what you consider
    to be "best".

    Once you have selected an algorithm, if you have problems coding it
    correctly in standard C, then you can post your code and description
    of your problem here.

    --
    Jack Klein
    Home: http://JK-Technology.Com
    FAQs for
    comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
    comp.lang.c++ http://www.parashift.com/c -faq-lite/
    alt.comp.lang.learn.c-c++
    http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html
     
    Jack Klein, Nov 25, 2005
    #3
  4. vietor.liu

    Mabden Guest

    What is the best colour?

    --
    Mabden
     
    Mabden, Dec 5, 2005
    #4
  5. vietor.liu

    Joe Estock Guest

    Mabden wrote:
    > What is the best colour?
    >


    Red. No wait, Purple. On second thought, make that Green.

    I have no idea what it is you are asking since both the subject line and
    the body of your post are completely different and no context is
    provided in either. Please be more descriptive when you post as it helps
    us better help you.

    Joe
     
    Joe Estock, Dec 5, 2005
    #5
  6. Joe Estock said:

    > Mabden wrote:
    >> What is the best colour?
    >>

    >
    > Red. No wait, Purple. On second thought, make that Green.


    ' . .
    ea e o ee e o a
    Pl s d n t f d th tr lls Th nks

    --
    Richard Heathfield
    "Usenet is a strange place" - dmr 29/7/1999
    http://www.cpax.org.uk
    email: rjh at above domain (but drop the www, obviously)
     
    Richard Heathfield, Dec 5, 2005
    #6
  7. Joe Estock <> wrote:

    > Red. No wait, Purple. On second thought, make that Green.


    And what is the airspeed velocity of an unladen swallow?

    --
    Christopher Benson-Manica | I *should* know what I'm talking about - if I
    ataru(at)cyberspace.org | don't, I need to know. Flames welcome.
     
    Christopher Benson-Manica, Dec 5, 2005
    #7
  8. vietor.liu

    Skarmander Guest

    Christopher Benson-Manica wrote:
    > Joe Estock <> wrote:
    >
    >> Red. No wait, Purple. On second thought, make that Green.

    >
    > And what is the airspeed velocity of an unladen swallow?
    >

    Please read http://www.ungerhu.com/jxh/clc.welcome.txt. Your question is
    off-topic for this group. You may have more success getting answers in
    comp.lang.python -- this may be a FAQ there.

    S.
     
    Skarmander, Dec 5, 2005
    #8
  9. vietor.liu

    pete Guest

    [ot]Re: what's the best hash function?

    Christopher Benson-Manica wrote:
    >
    > Joe Estock <> wrote:
    >
    > > Red. No wait, Purple. On second thought, make that Green.

    >
    > And what is the airspeed velocity of an unladen swallow?


    http://faultgame.com/images/quest.wav

    --
    pete
     
    pete, Dec 5, 2005
    #9
  10. Re: what's the best hash function?

    Christopher Benson-Manica wrote:
    > Joe Estock <> wrote:
    >
    > > Red. No wait, Purple. On second thought, make that Green.

    >
    > And what is the airspeed velocity of an unladen swallow?
    >
    > --
    > Christopher Benson-Manica | I *should* know what I'm talking about - if I
    > ataru(at)cyberspace.org | don't, I need to know. Flames welcome.


    This really sounds like homework. Besides, it is an algorithm
    question, so comp.programming would be a better place.
    Maybe you should try to write a C program to calculate
    the average velocity of a number of swallows. If you
    present your efforts, I'm sure people will try to give you a
    hand. <OT> Hint -- it matters whether it is African or
    European </OT>

    -David
     
    David Resnick, Dec 5, 2005
    #10
  11. On Mon, 05 Dec 2005 15:49:26 +0100, in comp.lang.c , Skarmander
    <> wrote:

    >Christopher Benson-Manica wrote:
    >
    >> And what is the airspeed velocity of an unladen swallow?
    >>

    >You may have more success getting answers in
    >comp.lang.python -- this may be a FAQ there.


    rofl!!!


    --
    Mark McIntyre
    CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
    CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt>

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    Mark McIntyre, Dec 5, 2005
    #11
  12. On Mon, 5 Dec 2005 14:44:43 +0000 (UTC), in comp.lang.c , Christopher
    Benson-Manica <> wrote:

    >Joe Estock <> wrote:
    >
    >> Red. No wait, Purple. On second thought, make that Green.

    >
    >And what is the airspeed velocity of an unladen swallow?


    African or European? http://www.style.org/unladenswallow/
    --
    Mark McIntyre
    CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
    CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt>

    ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
    http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
    ----= East and West-Coast Server Farms - Total Privacy via Encryption =----
     
    Mark McIntyre, Dec 5, 2005
    #12
  13. vietor.liu

    Jordan Abel Guest

    On 2005-12-05, Joe Estock <> wrote:
    > Mabden wrote:
    >> What is the best colour?
    >>

    >
    > Red. No wait, Purple. On second thought, make that Green.
    >
    > I have no idea what it is you are asking since both the subject line and
    > the body of your post are completely different and no context is
    > provided in either. Please be more descriptive when you post as it helps
    > us better help you.


    It seems to me that he's responding to the question in the subject with
    a rhetorical question, rather than responding to the body of the post he
    is in reply to.
     
    Jordan Abel, Dec 5, 2005
    #13
  14. vietor.liu

    Mabden Guest

    "Richard Heathfield" <> wrote in message
    news:dn1162$jue$-infra.bt.com...
    > Joe Estock said:
    >
    > > Mabden wrote:
    > >> What is the best colour?
    > >>

    > >
    > > Red. No wait, Purple. On second thought, make that Green.

    >
    > ' . .
    > ea e o ee e o a
    > Pl s d n t f d th tr lls Th nks
    >


    Buuuuurrrrp!

    Seriously, it was an answer to the post. How can one say what the best
    hash function is without knowing the data? I think my answer was quite
    appropos.

    --
    Mabden
     
    Mabden, Dec 6, 2005
    #14
  15. vietor.liu

    Mabden Guest

    "Christopher Benson-Manica" <> wrote in
    message news:dn1jor$8no$...
    > Joe Estock <> wrote:
    >
    > > Red. No wait, Purple. On second thought, make that Green.

    >
    > And what is the airspeed velocity of an unladen swallow?
    >


    http://www.style.org/unladenswallow/

    "the average cruising airspeed velocity of an unladen European Swallow
    is roughly 11 meters per second, or 24 miles an hour. "

    --
    Mabden
     
    Mabden, Dec 6, 2005
    #15
  16. vietor.liu

    Joe Estock Guest

    Mabden wrote:
    > "Richard Heathfield" <> wrote in message
    > news:dn1162$jue$-infra.bt.com...
    >
    >>Joe Estock said:
    >>
    >>
    >>>Mabden wrote:
    >>>
    >>>>What is the best colour?
    >>>>
    >>>
    >>>Red. No wait, Purple. On second thought, make that Green.

    >>
    >> ' . .
    >> ea e o ee e o a
    >>Pl s d n t f d th tr lls Th nks
    >>

    >
    >
    > Buuuuurrrrp!
    >
    > Seriously, it was an answer to the post. How can one say what the best
    > hash function is without knowing the data? I think my answer was quite
    > appropos.
    >


    If enough of the original post were left in your reply then I would be
    inclined to agree, however I had nothing but the text I replied to and
    misinterpreted your reply. Yet another classic example of why you should
    quote enough text from the previous post so that someone looking at the
    thread for the very first time has enough information to understand your
    reply. For all I know you could have been the OP replying to your
    original thread.

    Joe
     
    Joe Estock, Dec 6, 2005
    #16
  17. vietor.liu

    Mabden Guest

    "Joe Estock" <> wrote in message
    news:5H9lf.599651$x96.384071@attbi_s72...
    > Mabden wrote:
    > > "Richard Heathfield" <> wrote in message
    > > news:dn1162$jue$-infra.bt.com...
    > >>Joe Estock said:
    > >>>Mabden wrote:
    > >>>>What is the best colour?
    > >>>Red. No wait, Purple. On second thought, make that Green.
    > >> ' . .
    > >> ea e o ee e o a
    > >>Pl s d n t f d th tr lls Th nks

    > >
    > > Buuuuurrrrp!
    > >
    > > Seriously, it was an answer to the post. How can one say what the

    best
    > > hash function is without knowing the data? I think my answer was

    quite
    > > appropos.

    >
    > If enough of the original post were left in your reply then I would be
    > inclined to agree, however I had nothing but the text I replied to and
    > misinterpreted your reply. Yet another classic example of why you

    should
    > quote enough text from the previous post so that someone looking at

    the
    > thread for the very first time has enough information to understand

    your
    > reply. For all I know you could have been the OP replying to your
    > original thread.
    >



    It really wouldn't help. The subject says it all, but here it is, in all
    its 2-word glory:
    ======================
    is this?

    int hashpjw(char* str,int size)
    {
    unsigned long h=0,g;
    for(unsigned char *p=(unsigned char*)str;*p;++p)
    {
    h=(h<<4)+*p;
    if(g=(h&0xf0000000))
    {
    h^=(g>>24);
    h^=g;
    }
    }
    return h%size;
    }

    ======================

    Now, does that really need to have been included. I think not.

    I await your apology with anticip...
    ..
    ..
    ..
    ..
    ation

    --
    Mabden
     
    Mabden, Dec 7, 2005
    #17
  18. vietor.liu

    Joe Estock Guest

    [OT] Re: what's the best hash function?

    Mabden wrote:
    [snip irrelevant stuff to my reply]
    >>If enough of the original post were left in your reply then I would be
    >>inclined to agree, however I had nothing but the text I replied to and
    >>misinterpreted your reply. Yet another classic example of why you should
    >>quote enough text from the previous post so that someone looking at
    >>the thread for the very first time has enough information to understand
    >>your reply. For all I know you could have been the OP replying to your
    >>original thread.
    >>

    >
    >
    >
    > It really wouldn't help. The subject says it all, but here it is, in all
    > its 2-word glory:
    > ======================
    > is this?
    >

    [snip 14 lines of code for hash function]
    >
    > ======================
    >
    > Now, does that really need to have been included. I think not.


    I agree that it did not need to be included, however you could have at
    least included some context such as [snip useless function] so that
    others who do not have access to the original thread can better
    understand why you replied as you did.

    >
    > I await your apology with anticip...

    [snip gratuitous waste of newlines]
    > ation
    >


    None needed since I said nothing that demands an apology. I was simply
    pointing out that if you had quoted (or at least noted that you trimmed)
    the original post that I would not have replied as I did. You don't read
    the last message in a thread without first reading the original post and
    neither do I.

    Joe
     
    Joe Estock, Dec 8, 2005
    #18
  19. Re: [OT] Re: what's the best hash function?

    On Thu, 08 Dec 2005 06:19:53 GMT, in comp.lang.c , Joe Estock
    <> wrote:

    >Mabden wrote:
    >>
    >> I await your apology with anticip...

    >[snip gratuitous waste of newlines]


    I fear the joke went over your head.

    >> ation

    >
    >None needed


    And you shall recieve it, in abundance.

    gd&r



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    Mark McIntyre, Dec 8, 2005
    #19
  20. vietor.liu

    Jordan Abel Guest

    Re: [OT] Re: what's the best hash function?

    On 2005-12-08, Joe Estock <> wrote:
    >>
    >> I await your apology with anticip...

    > [snip gratuitous waste of newlines]


    it's not like we're killing trees, here - they probably only occupy a
    byte apiece in storage and two over the wire. Your complaint was almost
    certainly bigger.

    >> ation
    >>
     
    Jordan Abel, Dec 8, 2005
    #20
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