nss/nss_hash.c

   1 /* Copyright (c) 1997-2018 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Thorsten Kukuk <kukuk@suse.de>, 1997.
   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    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <nss.h>
  20
  21 /* This is from libc/db/hash/hash_func.c, hash3 is static there */
  22 /*
  23  * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
  24  * units.  On the first time through the loop we get the "leftover bytes"
  25  * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
  26  * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
  27  * this routine is heavily used enough, it's worth the ugly coding.
  28  *
  29  * OZ's original sdbm hash
  30  */
  31 uint32_t
  32 __nss_hash (const void *keyarg, size_t len)
  33 {
  34   const unsigned char *key;
  35   size_t loop;
  36   uint32_t h;
  37
  38 #define HASHC   h = *key++ + 65599 * h
  39
  40   h = 0;
  41   key = keyarg;
  42   if (len > 0)
  43     {
  44       loop = (len + 8 - 1) >> 3;
  45       switch (len & (8 - 1))
  46         {
  47         case 0:
  48           do
  49             {
  50               HASHC;
  51               /* FALLTHROUGH */
  52             case 7:
  53               HASHC;
  54               /* FALLTHROUGH */
  55             case 6:
  56               HASHC;
  57               /* FALLTHROUGH */
  58             case 5:
  59               HASHC;
  60               /* FALLTHROUGH */
  61             case 4:
  62               HASHC;
  63               /* FALLTHROUGH */
  64             case 3:
  65               HASHC;
  66               /* FALLTHROUGH */
  67             case 2:
  68               HASHC;
  69               /* FALLTHROUGH */
  70             case 1:
  71               HASHC;
  72             }
  73           while (--loop);
  74         }
  75     }
  76   return h;
  77 }
  78
  79 libc_hidden_def (__nss_hash)