XrdOucHashVal.cc

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/******************************************************************************/
/*                                                                            */
/*                      X r d O u c H a s h V a l . c c                       */
/*                                                                            */
/* (c) 2004 by the Board of Trustees of the Leland Stanford, Jr., University  */
/*   Produced by Andrew Hanushevsky for Stanford University under contract    */
/*              DE-AC02-76-SFO0515 with the Department of Energy              */
/*                                                                            */
/* This file is part of the XRootD software suite.                            */
/*                                                                            */
/* XRootD is free software: you can redistribute it and/or modify it under    */
/* the terms of the GNU Lesser General Public License as published by the     */
/* Free Software Foundation, either version 3 of the License, or (at your     */
/* option) any later version.                                                 */
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/* XRootD is distributed in the hope that it will be useful, but WITHOUT      */
/* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or      */
/* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public       */
/* License for more details.                                                  */
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/* You should have received a copy of the GNU Lesser General Public License   */
/* along with XRootD in a file called COPYING.LESSER (LGPL license) and file  */
/* COPYING (GPL license).  If not, see <http://www.gnu.org/licenses/>.        */
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/******************************************************************************/
 
#include "string.h"
#ifndef WIN32
#include "strings.h"
#endif
 
namespace
{
// Load n bytes of the key as a little-endian word, so that the hash does not
// depend on the byte order of the host.
//
unsigned long LoadWord(const char *cp, size_t n = sizeof(unsigned long))
{
   unsigned long w = 0;
   memcpy(&w, cp, n);
#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
   if (sizeof(w) == 8) w = __builtin_bswap64(w);
      else w = __builtin_bswap32(w);
#endif
   return w;
}
}
 
unsigned long XrdOucHashVal(const char *KeyVal)
         {extern unsigned long XrdOucHashVal2(const char *, int);
          return XrdOucHashVal2(KeyVal, strlen(KeyVal));
         }
 
unsigned long XrdOucHashVal2(const char *KeyVal, int KeyLen)
{  int j;
   const char *cp;
   unsigned long hval = 0;
   int hl = sizeof(hval);
 
// If name is shorter than the hash length, use the name.
//
   if (KeyLen <= hl) return LoadWord(KeyVal, (size_t)KeyLen);
 
// Compute the length of the name and develop starting hash.
//
   hval = KeyLen;
   j = KeyLen % hl; KeyLen /= hl;
   if (j) hval ^= LoadWord(KeyVal);
   cp = &KeyVal[j];
 
// Compute and return the full hash. The key is walked with a byte pointer
// since it is not aligned for unsigned long; LoadWord() does the unaligned
// load, and the word arithmetic happens on the copy.
//
   while(KeyLen--)
        {hval ^= LoadWord(cp);
         cp += hl;
        }
   return (hval ? hval : 1);
}