/* Copyright (C) 1991-2018 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

   <http://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)

{

  size_t len = strlen (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

    {

#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)