[PATCH 2/7] stdlib: Simplify getenv

[Adhemerval Zanella Netto]

On 16/02/23 15:47, Wilco Dijkstra wrote:
> Hi Adhemerval,
> 
>> Do you mean something like:
>>
>>   size_t len = strlen (name);;
>>   for (char **ep = __environ; *ep != NULL; ++ep)
>>     {
>>       if (((*ep)[0] == name[0] && (*ep)[1] == '=')
>>           || (strncmp (name, *ep, len) == 0 && (*ep)[len] == '='))
>>         return *ep + len + 1;
>>     }
> 
> No I meant checking the first character first before doing more expensive calls, so:
> 
>       if (name[0] == (*ep)[0] && strncmp (name, *ep, len) == 0 && (*ep)[len] == '=')
>         return *ep + len + 1;
> 
> Basically this means you get a very tight loop checking the first character - this avoids
> most calls to strncmp. This is basically the same result as the current implementation
> but without all the defines and complex unaligned/big-endian stuff!

Ah ok, I see it now.  Do the follow addresses the issues pointed out?


>From 373682e6c290f1c38d0319b5695e6a12a388be0c Mon Sep 17 00:00:00 2001
From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Thu, 9 Feb 2023 10:36:57 -0300
Subject: [PATCH 2/7] stdlib: Simplify getenv

And remove _STRING_ARCH_unaligned usage.

Checked on x86_64-linux-gnu and i686-linux-gnu.
---
 stdlib/getenv.c | 64 ++++---------------------------------------------
 1 file changed, 5 insertions(+), 59 deletions(-)

diff --git a/stdlib/getenv.c b/stdlib/getenv.c
index e3157ce2f3..6942d23433 100644
--- a/stdlib/getenv.c
+++ b/stdlib/getenv.c
@@ -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')
-    {
-      /* 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);;
+  for (char **ep = __environ; *ep != NULL; ++ep)
     {
-      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;
-- 
2.34.1