treewide nit: avoid NULL arithmetics

(u)intptr_t casts seem the best in terms of compliance:
https://stackoverflow.com/q/45220134/587396

Otherwise with clang 18 we can get warnings like
 ../$path:$line:$col: runtime error: applying non-zero offset $num to null pointer
 SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../$path:$line:$col

7 files changed, 13 insertions, 13 deletions

diff --git a/contrib/mempattern.c b/contrib/mempattern.c
index 6c237eac..e0c784de 100644
--- a/contrib/mempattern.c
+++ b/contrib/mempattern.c
@@ -125,7 +125,7 @@ void mm_ctx_mempool(knot_mm_t *mm, size_t chunk_size)
 
 void *mm_malloc_aligned(void *ctx, size_t n)
 {
-	size_t alignment = (size_t)ctx;
+	size_t alignment = (uintptr_t)ctx;
 	void *res;
 	int err = posix_memalign(&res, alignment, n);
 	if (err == 0) {
diff --git a/contrib/mempattern.h b/contrib/mempattern.h
index 4db147ae..7cb2bae8 100644
--- a/contrib/mempattern.h
+++ b/contrib/mempattern.h
@@ -81,7 +81,7 @@ static inline void mm_ctx_init_aligned(knot_mm_t *mm, size_t alignment)
 {
 	assert(__builtin_popcount(alignment) == 1);
 	mm_ctx_init(mm);
-	mm->ctx = (uint8_t *)NULL + alignment; /*< roundabout to satisfy linters */
+	mm->ctx = (void *)(uintptr_t)alignment; /*< roundabout to satisfy linters */
 	/* posix_memalign() doesn't allow alignment < sizeof(void*),
 	 * and there's no point in using it for small values anyway,
 	 * as plain malloc() guarantees at least max_align_t. */
diff --git a/daemon/bindings/net.c b/daemon/bindings/net.c
index aaeef238..55e9a914 100644
--- a/daemon/bindings/net.c
+++ b/daemon/bindings/net.c
@@ -1191,7 +1191,7 @@ static int net_register_endpoint_kind(lua_State *L)
 	if (param_count == 1) {
 		void *val;
 		if (trie_del(the_network->endpoint_kinds, kind, kind_len, &val) == KNOT_EOK) {
-			const int fun_id = (char *)val - (char *)NULL;
+			const int fun_id = (intptr_t)val;
 			luaL_unref(L, LUA_REGISTRYINDEX, fun_id);
 			return 0;
 		}
@@ -1209,7 +1209,7 @@ static int net_register_endpoint_kind(lua_State *L)
 	if (!pp) lua_error_maybe(L, kr_error(ENOMEM));
 	if (*pp != NULL || !strcasecmp(kind, "dns") || !strcasecmp(kind, "tls"))
 		lua_error_p(L, "attempt to register known kind '%s'\n", kind);
-	*pp = (char *)NULL + fun_id;
+	*pp = (void *)(intptr_t)fun_id;
 	/* We don't attempt to engage corresponding endpoints now.
 	 * That's the job for network_engage_endpoints() later. */
 	return 0;
diff --git a/daemon/network.c b/daemon/network.c
index 1ec34e90..7d1d5155 100644
--- a/daemon/network.c
+++ b/daemon/network.c
@@ -102,7 +102,7 @@ static int endpoint_open_lua_cb(struct endpoint *ep,
 	if (!pp) return kr_ok();
 
 	/* Now execute the callback. */
-	const int fun_id = (char *)*pp - (char *)NULL;
+	const int fun_id = (intptr_t)*pp;
 	lua_rawgeti(L, LUA_REGISTRYINDEX, fun_id);
 	lua_pushboolean(L, true /* open */);
 	lua_pushpointer(L, ep);
@@ -182,7 +182,7 @@ static void endpoint_close_lua_cb(struct endpoint *ep)
 	}
 	if (!pp) return;
 
-	const int fun_id = (char *)*pp - (char *)NULL;
+	const int fun_id = (intptr_t)*pp;
 	lua_rawgeti(L, LUA_REGISTRYINDEX, fun_id);
 	lua_pushboolean(L, false /* close */);
 	lua_pushpointer(L, ep);
@@ -262,7 +262,7 @@ static int free_key(trie_val_t *val, void* ext)
 
 int kind_unregister(trie_val_t *tv, void *L)
 {
-	int fun_id = (char *)*tv - (char *)NULL;
+	int fun_id = (intptr_t)*tv;
 	luaL_unref(L, LUA_REGISTRYINDEX, fun_id);
 	return 0;
 }
diff --git a/lib/generic/lru.c b/lib/generic/lru.c
index 857b20b3..71b8730b 100644
--- a/lib/generic/lru.c
+++ b/lib/generic/lru.c
@@ -50,9 +50,9 @@ static uint item_size(const struct lru *lru, uint key_len, uint val_len)
 /** @internal Return pointer to value in an lru_item. */
 static void * item_val(const struct lru *lru, struct lru_item *it)
 {
-	size_t key_end = it->data + it->key_len - (char *)NULL;
+	size_t key_end = (uintptr_t)(it->data + it->key_len);
 	size_t val_begin = round_power(key_end, lru->val_alignment);
-	return (char *)NULL + val_begin;
+	return (void *)(uintptr_t)val_begin;
 }
 
 /** @internal Free each item. */
diff --git a/lib/generic/test_trie.c b/lib/generic/test_trie.c
index 9ecd67cd..ce164906 100644
--- a/lib/generic/test_trie.c
+++ b/lib/generic/test_trie.c
@@ -48,7 +48,7 @@ static void test_insert(void **state)
 		trie_val_t *data = trie_get_ins(t, dict[i], KEY_LEN(dict[i]));
 		assert_non_null(data);
 		assert_null(*data);
-		*data = (char *)NULL + i; // yes, ugly
+		*data = (void *)(intptr_t)i; // yes, ugly
 		assert_ptr_equal(trie_get_try(t, dict[i], KEY_LEN(dict[i])), data);
 	}
 	assert_int_equal(trie_weight(t), dict_size);
@@ -82,7 +82,7 @@ static void test_iter(void **state)
 		const char *key = trie_it_key(it, &len);
 		assert_int_equal(KEY_LEN(key), len);
 		assert_string_equal(key, dict_sorted[i]);
-		assert_ptr_equal(dict[(char *)*trie_it_val(it) - (char *)NULL],
+		assert_ptr_equal(dict[(uintptr_t)*trie_it_val(it)],
 				 dict_sorted[i]);
 	}
 	assert_true(trie_it_finished(it));
@@ -100,7 +100,7 @@ static void test_queue(void **state)
 		assert_non_null(key);
 		assert_int_equal(len, KEY_LEN(key));
 		assert_non_null(data);
-		ptrdiff_t key_i = (char *)*data - (char *)NULL;
+		uintptr_t key_i = (uintptr_t)*data;
 		assert_string_equal(key, dict[key_i]);
 
 		len = 30;
diff --git a/lib/generic/trie.c b/lib/generic/trie.c
index 21254eb4..e2ce061e 100644
--- a/lib/generic/trie.c
+++ b/lib/generic/trie.c
@@ -116,7 +116,7 @@ static inline void empty_root(node_t *root) {
 static void assert_portability(void) {
 #if FLAGS_HACK
 	kr_require(((union node){ .leaf = {
-			.key = (tkey_t *)(((uint8_t *)NULL) + 1),
+			.key = (tkey_t *)(void *)(uintptr_t)1,
 			.val = NULL
 		} }).branch.flags == 1);
 #endif