1  /* Copyright (c) 1997-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <nss.h>
      19  
      20  /* This is from libc/db/hash/hash_func.c, hash3 is static there */
      21  /*
      22   * This is INCREDIBLY ugly, but fast.  We break the string up into 4 byte
      23   * units.  On the first time through the loop we get the "leftover bytes"
      24   * (len % 4).  On every other iteration, we perform a 4x unrolled version
      25   * HASHC. Further unrolling does not appear to help.
      26   *
      27   * OZ's original sdbm hash
      28   */
      29  uint32_t
      30  __nss_hash (const void *keyarg, size_t len)
      31  {
      32    enum
      33    {
      34      HASH_CONST_P0 = 1,	       /* (uint32_t)(65599 ^ 0).  */
      35      HASH_CONST_P1 = 65599,     /* (uint32_t)(65599 ^ 1).  */
      36      HASH_CONST_P2 = 8261505,   /* (uint32_t)(65599 ^ 2).  */
      37      HASH_CONST_P3 = 780587199, /* (uint32_t)(65599 ^ 3).  */
      38      HASH_CONST_P4 = 1139564289 /* (uint32_t)(65599 ^ 4).  */
      39    };
      40  
      41    const unsigned char *key;
      42    uint32_t h;
      43  
      44  #define HASHC	h = *key++ + HASH_CONST_P1 * h
      45  
      46    h = 0;
      47    key = keyarg;
      48    if (len > 0)
      49      {
      50        switch ((len & (4 - 1)))
      51  	{
      52  	case 0:
      53  	  /* h starts out as zero so no need to include the multiply. */
      54  	  h = *key++;
      55  	  /* FALLTHROUGH */
      56  	case 3:
      57  	  HASHC;
      58  	  /* FALLTHROUGH */
      59  	case 2:
      60  	  HASHC;
      61  	  /* FALLTHROUGH */
      62  	case 1:
      63  	  HASHC;
      64  	  /* FALLTHROUGH */
      65  	}
      66  
      67        uint32_t c0, c1, c2, c3;
      68        for (--len; len >= 4; len -= 4)
      69  	{
      70  	  c0 = (unsigned char) *(key + 0);
      71  	  c1 = (unsigned char) *(key + 1);
      72  	  c2 = (unsigned char) *(key + 2);
      73  	  c3 = (unsigned char) *(key + 3);
      74  	  h = HASH_CONST_P4 * h + HASH_CONST_P3 * c0 + HASH_CONST_P2 * c1
      75  	      + HASH_CONST_P1 * c2 + HASH_CONST_P0 * c3;
      76  
      77  	  key += 4;
      78  	}
      79      }
      80    return h;
      81  }
      82  
      83  
      84  libc_hidden_def (__nss_hash)