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stdlib: Simplify getenv

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And remove _STRING_ARCH_unaligned usage.

Checked on x86_64-linux-gnu and i686-linux-gnu.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
This commit is contained in:
Adhemerval Zanella 2023-02-09 10:36:57 -03:00
parent 11053fd424
commit a6ccce23af
1 changed files with 5 additions and 59 deletions
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64
stdlib/getenv.c
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@ -15,76 +15,22 @@
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')
size_t len = strlen (name);
for (char **ep = __environ; *ep != NULL; ++ep)
{
/* 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];
}
if (name[0] == (*ep)[0]
&& strncmp (name, *ep, len) == 0 && (*ep)[len] == '=')
return *ep + len + 1;
}
return NULL;