aboutsummaryrefslogtreecommitdiff
path: root/stdlib/getenv.c
diff options
context:
space:
mode:
Diffstat (limited to 'stdlib/getenv.c')
-rw-r--r--stdlib/getenv.c98
1 files changed, 98 insertions, 0 deletions
diff --git a/stdlib/getenv.c b/stdlib/getenv.c
new file mode 100644
index 0000000..6cdfe2b
--- /dev/null
+++ b/stdlib/getenv.c
@@ -0,0 +1,98 @@
+/* Copyright (C) 1991,92,94,96,98,99,2002,2005 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, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#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 (name)
+ 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
+# if __BYTE_ORDER == __BIG_ENDIAN
+ name_start = '=' | ((*(const unsigned char *) name) << 8);
+# else
+ #error "Funny byte order."
+# endif
+#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)