nss/nss_hash.c

   1 /* Copyright (c) 1997-2022 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 8 byte
  23  * units.  On the first time through the loop we get the "leftover bytes"
  24  * (strlen % 8).  On every other iteration, we perform 8 HASHC's so we handle
  25  * all 8 bytes.  Essentially, this saves us 7 cmp & branch instructions.  If
  26  * this routine is heavily used enough, it's worth the ugly coding.
  27  *
  28  * OZ's original sdbm hash
  29  */
  30 uint32_t
  31 __nss_hash (const void *keyarg, size_t len)
  32 {
  33   const unsigned char *key;
  34   size_t loop;
  35   uint32_t h;
  36
  37 #define HASHC   h = *key++ + 65599 * h
  38
  39   h = 0;
  40   key = keyarg;
  41   if (len > 0)
  42     {
  43       loop = (len + 8 - 1) >> 3;
  44       switch (len & (8 - 1))
  45         {
  46         case 0:
  47           do
  48             {
  49               HASHC;
  50               /* FALLTHROUGH */
  51             case 7:
  52               HASHC;
  53               /* FALLTHROUGH */
  54             case 6:
  55               HASHC;
  56               /* FALLTHROUGH */
  57             case 5:
  58               HASHC;
  59               /* FALLTHROUGH */
  60             case 4:
  61               HASHC;
  62               /* FALLTHROUGH */
  63             case 3:
  64               HASHC;
  65               /* FALLTHROUGH */
  66             case 2:
  67               HASHC;
  68               /* FALLTHROUGH */
  69             case 1:
  70               HASHC;
  71             }
  72           while (--loop);
  73         }
  74     }
  75   return h;
  76 }
  77
  78 libc_hidden_def (__nss_hash)