| lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | /* Copyright (C) 1991-2015 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 | <http://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. */ |
| 32 | char * |
| 33 | getenv (name) |
| 34 | const char *name; |
| 35 | { |
| 36 | size_t len = strlen (name); |
| 37 | char **ep; |
| 38 | uint16_t name_start; |
| 39 | |
| 40 | if (__environ == NULL || name[0] == '\0') |
| 41 | return NULL; |
| 42 | |
| 43 | if (name[1] == '\0') |
| 44 | { |
| 45 | /* The name of the variable consists of only one character. Therefore |
| 46 | the first two characters of the environment entry are this character |
| 47 | and a '=' character. */ |
| 48 | #if __BYTE_ORDER == __LITTLE_ENDIAN || !_STRING_ARCH_unaligned |
| 49 | name_start = ('=' << 8) | *(const unsigned char *) name; |
| 50 | #else |
| 51 | name_start = '=' | ((*(const unsigned char *) name) << 8); |
| 52 | #endif |
| 53 | for (ep = __environ; *ep != NULL; ++ep) |
| 54 | { |
| 55 | #if _STRING_ARCH_unaligned |
| 56 | uint16_t ep_start = *(uint16_t *) *ep; |
| 57 | #else |
| 58 | uint16_t ep_start = (((unsigned char *) *ep)[0] |
| 59 | | (((unsigned char *) *ep)[1] << 8)); |
| 60 | #endif |
| 61 | if (name_start == ep_start) |
| 62 | return &(*ep)[2]; |
| 63 | } |
| 64 | } |
| 65 | else |
| 66 | { |
| 67 | #if _STRING_ARCH_unaligned |
| 68 | name_start = *(const uint16_t *) name; |
| 69 | #else |
| 70 | name_start = (((const unsigned char *) name)[0] |
| 71 | | (((const unsigned char *) name)[1] << 8)); |
| 72 | #endif |
| 73 | len -= 2; |
| 74 | name += 2; |
| 75 | |
| 76 | for (ep = __environ; *ep != NULL; ++ep) |
| 77 | { |
| 78 | #if _STRING_ARCH_unaligned |
| 79 | uint16_t ep_start = *(uint16_t *) *ep; |
| 80 | #else |
| 81 | uint16_t ep_start = (((unsigned char *) *ep)[0] |
| 82 | | (((unsigned char *) *ep)[1] << 8)); |
| 83 | #endif |
| 84 | |
| 85 | if (name_start == ep_start && !strncmp (*ep + 2, name, len) |
| 86 | && (*ep)[len + 2] == '=') |
| 87 | return &(*ep)[len + 3]; |
| 88 | } |
| 89 | } |
| 90 | |
| 91 | return NULL; |
| 92 | } |
| 93 | libc_hidden_def (getenv) |