nis/nis_hash.c

   1 /* Copyright (c) 1997-2017 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 <stdint.h>
  20 #include <rpcsvc/nis.h>
  21
  22 /* This is from libc/db/hash/hash_func.c, hash3 is static there */
  23 /*
  24  * This is INCREDIBLY ugly, but fast.  We break the string up into 8 byte
  25  * units.  On the first time through the loop we get the "leftover bytes"
  26  * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
  27  * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
  28  * this routine is heavily used enough, it's worth the ugly coding.
  29  *
  30  * OZ's original sdbm hash
  31  */
  32 uint32_t
  33 __nis_hash (const void *keyarg, size_t len)
  34 {
  35   const u_char *key;
  36   size_t loop;
  37   uint32_t h;
  38
  39 #define HASHC   h = *key++ + 65599 * h
  40
  41   h = 0;
  42   key = keyarg;
  43   if (len > 0)
  44     {
  45       loop = (len + 8 - 1) >> 3;
  46       switch (len & (8 - 1))
  47         {
  48         case 0:
  49           do {
  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           } while (--loop);
  73         }
  74     }
  75   return h;
  76 }