Path: utzoo!utgpu!water!watmath!clyde!rutgers!cbmvax!carolyn
From: carolyn@cbmvax.UUCP (Carolyn Scheppner CATS)
Newsgroups: comp.sys.amiga
Subject: Re: The AmigaDos Hash function, how???
Message-ID: <3163@cbmvax.UUCP>
Date: 19 Jan 88 14:27:36 GMT
References: <8801182112.AA24295@jade.berkeley.edu>
Reply-To: carolyn@cbmvax.UUCP (Carolyn Scheppner CATS)
Organization: Commodore Technology, West Chester, PA
Lines: 43

In article <8801182112.AA24295@jade.berkeley.edu> RCST12@HEITHE5.BITNET writes:
>Subject: AmigaDos hash function, how???
>
>
>A friend of mine is writing a disk-editor, and he ran into a problem
>when he wanted to put some amigados knowledge into it.
>The question is : How does the hashfunction work??


   HASH FUNCTION

   The hash function is applied to the name of a file or directory, and the
resulting value provides an offset into the HashTable which contains either
zero or a key to the first block on a chain linking blocks with the same
hash value.  Each block contains a name field which identifies it.  The
directory and file header block fields are described in the AmigaDOS manual.
 

int HashName(str,hlen)
 
char    *str;           /* The string to find the hash number for       */
int     hlen;           /* The length of the hash table                 */
 
{
  char  xchar;
  int   i, result;

  result = strlen(str);
  for (i=0; i<strlen(str); i++) {
    if (isalpha(str[i])) xchar = toupper(str[i]);
    else xchar = str[i];
    result = ((result * 13) + xchar) & 0x7ff;
  }
  result = result % hlen;
  return(result);
}

-- 
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Carolyn Scheppner -- CATS   >>Commodore Amiga Technical Support<<
                     UUCP  ...{allegra,ihnp4,rutgers}!cbmvax!carolyn 
                     PHONE 215-431-9180
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