mirror of git://sourceware.org/git/glibc.git
94 lines
2.8 KiB
C
94 lines
2.8 KiB
C
/* Copyright (C) 1991-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <endian.h>
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#include <errno.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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/* Return the value of the environment variable NAME. This implementation
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is tuned a bit in that it assumes no environment variable has an empty
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name which of course should always be true. We have a special case for
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one character names so that for the general case we can assume at least
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two characters which we can access. By doing this we can avoid using the
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`strncmp' most of the time. */
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char *
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getenv (name)
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const char *name;
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{
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size_t len = strlen (name);
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char **ep;
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uint16_t name_start;
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if (__environ == NULL || name[0] == '\0')
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return NULL;
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if (name[1] == '\0')
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{
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/* The name of the variable consists of only one character. Therefore
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the first two characters of the environment entry are this character
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and a '=' character. */
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#if __BYTE_ORDER == __LITTLE_ENDIAN || !_STRING_ARCH_unaligned
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name_start = ('=' << 8) | *(const unsigned char *) name;
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#else
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name_start = '=' | ((*(const unsigned char *) name) << 8);
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#endif
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for (ep = __environ; *ep != NULL; ++ep)
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{
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#if _STRING_ARCH_unaligned
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uint16_t ep_start = *(uint16_t *) *ep;
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#else
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uint16_t ep_start = (((unsigned char *) *ep)[0]
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| (((unsigned char *) *ep)[1] << 8));
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#endif
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if (name_start == ep_start)
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return &(*ep)[2];
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}
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}
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else
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{
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#if _STRING_ARCH_unaligned
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name_start = *(const uint16_t *) name;
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#else
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name_start = (((const unsigned char *) name)[0]
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| (((const unsigned char *) name)[1] << 8));
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#endif
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len -= 2;
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name += 2;
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for (ep = __environ; *ep != NULL; ++ep)
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{
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#if _STRING_ARCH_unaligned
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uint16_t ep_start = *(uint16_t *) *ep;
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#else
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uint16_t ep_start = (((unsigned char *) *ep)[0]
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| (((unsigned char *) *ep)[1] << 8));
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#endif
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if (name_start == ep_start && !strncmp (*ep + 2, name, len)
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&& (*ep)[len + 2] == '=')
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return &(*ep)[len + 3];
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}
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}
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return NULL;
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}
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libc_hidden_def (getenv)
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