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/* Copyright (C) 1991-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <endian.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* Return the value of the environment variable NAME. This implementation
is tuned a bit in that it assumes no environment variable has an empty
name which of course should always be true. We have a special case for
one character names so that for the general case we can assume at least
two characters which we can access. By doing this we can avoid using the
`strncmp' most of the time. */
char *
getenv (const char *name)
{
char **ep;
uint16_t name_start;
if (__environ == NULL || name[0] == '\0')
return NULL;
if (name[1] == '\0')
{
/* The name of the variable consists of only one character. Therefore
the first two characters of the environment entry are this character
and a '=' character. */
#if __BYTE_ORDER == __LITTLE_ENDIAN || !_STRING_ARCH_unaligned
name_start = ('=' << 8) | *(const unsigned char *) name;
#else
name_start = '=' | ((*(const unsigned char *) name) << 8);
#endif
for (ep = __environ; *ep != NULL; ++ep)
{
#if _STRING_ARCH_unaligned
uint16_t ep_start = *(uint16_t *) *ep;
#else
uint16_t ep_start = (((unsigned char *) *ep)[0]
| (((unsigned char *) *ep)[1] << 8));
#endif
if (name_start == ep_start)
return &(*ep)[2];
}
}
else
{
size_t len = strlen (name);
#if _STRING_ARCH_unaligned
name_start = *(const uint16_t *) name;
#else
name_start = (((const unsigned char *) name)[0]
| (((const unsigned char *) name)[1] << 8));
#endif
len -= 2;
name += 2;
for (ep = __environ; *ep != NULL; ++ep)
{
#if _STRING_ARCH_unaligned
uint16_t ep_start = *(uint16_t *) *ep;
#else
uint16_t ep_start = (((unsigned char *) *ep)[0]
| (((unsigned char *) *ep)[1] << 8));
#endif
if (name_start == ep_start && !strncmp (*ep + 2, name, len)
&& (*ep)[len + 2] == '=')
return &(*ep)[len + 3];
}
}
return NULL;
}
libc_hidden_def (getenv)
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