1  /* Compute hash value for given string according to ELF standard.
       2     Copyright (C) 1995-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       4  
       5     The GNU C Library is free software; you can redistribute it and/or
       6     modify it under the terms of the GNU Lesser General Public
       7     License as published by the Free Software Foundation; either
       8     version 2.1 of the License, or (at your option) any later version.
       9  
      10     The GNU C Library is distributed in the hope that it will be useful,
      11     but WITHOUT ANY WARRANTY; without even the implied warranty of
      12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      13     Lesser General Public License for more details.
      14  
      15     You should have received a copy of the GNU Lesser General Public
      16     License along with the GNU C Library; if not, see
      17     <https://www.gnu.org/licenses/>.  */
      18  
      19  #ifndef _DL_HASH_H
      20  #define _DL_HASH_H	1
      21  
      22  
      23  /* This is the hashing function specified by the ELF ABI.  In the
      24     first five operations no overflow is possible so we optimized it a
      25     bit.  */
      26  static unsigned int
      27  __attribute__ ((unused))
      28  _dl_elf_hash (const char *name_arg)
      29  {
      30    const unsigned char *name = (const unsigned char *) name_arg;
      31    unsigned long int hash = *name;
      32    if (hash != 0 && name[1] != '\0')
      33      {
      34        hash = (hash << 4) + name[1];
      35        if (name[2] != '\0')
      36  	{
      37  	  hash = (hash << 4) + name[2];
      38  	  if (name[3] != '\0')
      39  	    {
      40  	      hash = (hash << 4) + name[3];
      41  	      if (name[4] != '\0')
      42  		{
      43  		  hash = (hash << 4) + name[4];
      44  		  name += 5;
      45  		  while (*name != '\0')
      46  		    {
      47  		      unsigned long int hi;
      48  		      hash = (hash << 4) + *name++;
      49  		      hi = hash & 0xf0000000;
      50  
      51  		      /* The algorithm specified in the ELF ABI is as
      52  			 follows:
      53  
      54  			 if (hi != 0)
      55  			   hash ^= hi >> 24;
      56  
      57  			 hash &= ~hi;
      58  
      59  			 But the following is equivalent and a lot
      60  			 faster, especially on modern processors.  */
      61  
      62  		      hash ^= hi >> 24;
      63  		    }
      64  
      65  		  /* Second part of the modified formula.  This
      66  		     operation can be lifted outside the loop.  */
      67  		  hash &= 0x0fffffff;
      68  		}
      69  	    }
      70  	}
      71      }
      72    return hash;
      73  }
      74  
      75  #endif /* dl-hash.h */