Optimize prev. commit for speed.

1) Don't iterate the loop from the environment array beginning each time,
iterate it under the last place we deactivate instead.
2) Call __rebuild_environ() not on each iteration but once, only at the end
of whole loop (of course, only in case if something is changed).

MFC after:      1 week

1 files changed, 7 insertions, 3 deletions

diff --git a/lib/libc/stdlib/getenv.c b/lib/libc/stdlib/getenv.c
index 37602a915f40..47963d53dd62 100644
--- a/lib/libc/stdlib/getenv.c
+++ b/lib/libc/stdlib/getenv.c
@@ -662,6 +662,7 @@ unsetenv(const char *name)
 {
 	int envNdx;
 	size_t nameLen;
+	int newEnvActive;
 
 	/* Check for malformed name. */
 	if (name == NULL || (nameLen = __strleneq(name)) == 0) {
@@ -674,15 +675,18 @@ unsetenv(const char *name)
 		return (-1);
 
 	/* Deactivate specified variable. */
-	envNdx = envVarsTotal - 1;
 	/* Remove all occurrences. */
+	envNdx = envVarsTotal - 1;
+	newEnvActive = envActive;
 	while (__findenv(name, nameLen, &envNdx, true) != NULL) {
 		envVars[envNdx].active = false;
 		if (envVars[envNdx].putenv)
 			__remove_putenv(envNdx);
-		__rebuild_environ(envActive - 1);
-		envNdx = envVarsTotal - 1;
+		envNdx--;
+		newEnvActive--;
 	}
+	if (newEnvActive != envActive)
+		__rebuild_environ(newEnvActive);
 
 	return (0);
 }