1 /* Copyright (c) 1997-2021 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
__nss_hash(const void * keyarg,size_t len)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)
79