1/* Copyright (C) 1991-2020 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 <endian.h>
19#include <errno.h>
20#include <stdint.h>
21#include <stdlib.h>
22#include <string.h>
23#include <unistd.h>
24
25
26/* Return the value of the environment variable NAME. This implementation
27 is tuned a bit in that it assumes no environment variable has an empty
28 name which of course should always be true. We have a special case for
29 one character names so that for the general case we can assume at least
30 two characters which we can access. By doing this we can avoid using the
31 `strncmp' most of the time. */
32char *
33getenv (const char *name)
34{
35 size_t len = strlen (name);
36 char **ep;
37 uint16_t name_start;
38
39 if (__environ == NULL || name[0] == '\0')
40 return NULL;
41
42 if (name[1] == '\0')
43 {
44 /* The name of the variable consists of only one character. Therefore
45 the first two characters of the environment entry are this character
46 and a '=' character. */
47#if __BYTE_ORDER == __LITTLE_ENDIAN || !_STRING_ARCH_unaligned
48 name_start = ('=' << 8) | *(const unsigned char *) name;
49#else
50 name_start = '=' | ((*(const unsigned char *) name) << 8);
51#endif
52 for (ep = __environ; *ep != NULL; ++ep)
53 {
54#if _STRING_ARCH_unaligned
55 uint16_t ep_start = *(uint16_t *) *ep;
56#else
57 uint16_t ep_start = (((unsigned char *) *ep)[0]
58 | (((unsigned char *) *ep)[1] << 8));
59#endif
60 if (name_start == ep_start)
61 return &(*ep)[2];
62 }
63 }
64 else
65 {
66#if _STRING_ARCH_unaligned
67 name_start = *(const uint16_t *) name;
68#else
69 name_start = (((const unsigned char *) name)[0]
70 | (((const unsigned char *) name)[1] << 8));
71#endif
72 len -= 2;
73 name += 2;
74
75 for (ep = __environ; *ep != NULL; ++ep)
76 {
77#if _STRING_ARCH_unaligned
78 uint16_t ep_start = *(uint16_t *) *ep;
79#else
80 uint16_t ep_start = (((unsigned char *) *ep)[0]
81 | (((unsigned char *) *ep)[1] << 8));
82#endif
83
84 if (name_start == ep_start && !strncmp (*ep + 2, name, len)
85 && (*ep)[len + 2] == '=')
86 return &(*ep)[len + 3];
87 }
88 }
89
90 return NULL;
91}
92libc_hidden_def (getenv)
93