basic: massively reduce the size of arphdr lookup functions

Our biggest object in libsystemd was a table full of zeros, for the arphdr
names. Let's use a switch (which gcc nicely optimizes for us), instead a
table with a gap between 826 and 65534:

$ ls -l build{,2}/src/basic/a6ba3eb@@basic@sta/arphrd-list.c.o
-rw-rw-r--. 1 zbyszek zbyszek 540232 Sep 22 00:29 build/src/basic/a6ba3eb\@\@basic\@sta/arphrd-list.c.o
-rw-rw-r--. 1 zbyszek zbyszek  20512 Sep 25 11:56 build2/src/basic/a6ba3eb\@\@basic\@sta/arphrd-list.c.o

$ ls -l build{,2}/src/shared/libsystemd-shared-243.so
-rwxrwxr-x. 1 zbyszek zbyszek 6774368 Sep 22 00:29 build/src/shared/libsystemd-shared-243.so
-rwxrwxr-x. 1 zbyszek zbyszek 6254808 Sep 25 12:16 build2/src/shared/libsystemd-shared-243.so

No functional change.

src/basic/arphrd-list.c

@@ -12,17 +12,6 @@ static const struct arphrd_name* lookup_arphrd(register const char *str, registe
 #include "arphrd-from-name.h"
 #include "arphrd-to-name.h"
 
-const char *arphrd_to_name(int id) {
-
-        if (id <= 0)
-                return NULL;
-
-        if ((size_t) id >= ELEMENTSOF(arphrd_names))
-                return NULL;
-
-        return arphrd_names[id];
-}
-
 int arphrd_from_name(const char *name) {
         const struct arphrd_name *sc;
 
@@ -34,7 +23,3 @@ int arphrd_from_name(const char *name) {
 
         return sc->id;
 }
-
-int arphrd_max(void) {
-        return ELEMENTSOF(arphrd_names);
-}

src/basic/arphrd-list.h

@@ -3,5 +3,3 @@
 
 const char *arphrd_to_name(int id);
 int arphrd_from_name(const char *name);
-
-int arphrd_max(void);

src/basic/arphrd-to-name.awk

@@ -1,9 +1,12 @@
 BEGIN{
-        print "static const char* const arphrd_names[] = { "
+        print "const char *arphrd_to_name(int id) {"
+        print "        switch(id) {"
 }
-!/CISCO/ {
-        printf "        [ARPHRD_%s] = \"%s\",\n", $1, $1
+!/CISCO|NETROM/ {
+        printf "        case ARPHRD_%s: return \"%s\";\n", $1, $1
 }
 END{
-        print "};"
+        print "        default: return NULL;"
+        print "        }"
+        print "}"
 }

src/test/test-arphrd-list.c

@@ -1,31 +1,27 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
 #include <linux/if_arp.h>
-#include <string.h>
 
-#include "macro.h"
 #include "string-util.h"
 #include "tests.h"
 
-_unused_ \
-static const struct arphrd_name* lookup_arphrd(register const char *str, register GPERF_LEN_TYPE len);
-
-#include "arphrd-from-name.h"
 #include "arphrd-list.h"
-#include "arphrd-to-name.h"
 
 int main(int argc, const char *argv[]) {
         test_setup_logging(LOG_INFO);
 
-        for (unsigned i = 1; i < ELEMENTSOF(arphrd_names); i++)
-                if (arphrd_names[i]) {
-                        log_info("%i: %s", i, arphrd_to_name(i));
+        for (int i = 0; i <= ARPHRD_VOID + 1; i++) {
+                const char *name;
 
-                        assert_se(streq(arphrd_to_name(i), arphrd_names[i]));
-                        assert_se(arphrd_from_name(arphrd_names[i]) == (int) i);
+                name = arphrd_to_name(i);
+                if (name) {
+                        log_info("%i: %s", i, name);
+
+                        assert_se(arphrd_from_name(name) == i);
                 }
+        }
 
-        assert_se(arphrd_to_name(arphrd_max()) == NULL);
+        assert_se(arphrd_to_name(ARPHRD_VOID + 1) == NULL);
         assert_se(arphrd_to_name(0) == NULL);
         assert_se(arphrd_from_name("huddlduddl") == -EINVAL);
         assert_se(arphrd_from_name("") == -EINVAL);