tree-wide: add global ascii_isdigit() + ascii_isalpha()

We now have a local implementation in string-util-fundamental.c, but
it's useful at a lot of other places, hence let's give it a more
expressive name and share it across the tree.

Follow-up for: 8d9156660d

src/basic/bus-label.c

@@ -26,12 +26,10 @@ char *bus_label_escape(const char *s) {
 
         for (f = s, t = r; *f; f++) {
 
-                /* Escape everything that is not a-zA-Z0-9. We also
-                 * escape 0-9 if it's the first character */
+                /* Escape everything that is not a-zA-Z0-9. We also escape 0-9 if it's the first character */
 
-                if (!(*f >= 'A' && *f <= 'Z') &&
-                    !(*f >= 'a' && *f <= 'z') &&
-                    !(f > s && *f >= '0' && *f <= '9')) {
+                if (!ascii_isalpha(*f) &&
+                    !(f > s && ascii_isdigit(*f))) {
                         *(t++) = '_';
                         *(t++) = hexchar(*f >> 4);
                         *(t++) = hexchar(*f);

src/basic/env-util.c

@@ -32,7 +32,7 @@ static bool env_name_is_valid_n(const char *e, size_t n) {
         if (n <= 0)
                 return false;
 
-        if (e[0] >= '0' && e[0] <= '9')
+        if (ascii_isdigit(e[0]))
                 return false;
 
         /* POSIX says the overall size of the environment block cannot

src/basic/hostname-util.c

@@ -75,10 +75,8 @@ int gethostname_full(GetHostnameFlags flags, char **ret) {
 bool valid_ldh_char(char c) {
         /* "LDH" → "Letters, digits, hyphens", as per RFC 5890, Section 2.3.1 */
 
-        return
-                (c >= 'a' && c <= 'z') ||
-                (c >= 'A' && c <= 'Z') ||
-                (c >= '0' && c <= '9') ||
+        return ascii_isalpha(c) ||
+                ascii_isdigit(c) ||
                 c == '-';
 }
 

src/basic/parse-util.c

@@ -210,7 +210,7 @@ int parse_size(const char *t, uint64_t base, uint64_t *size) {
                         e++;
 
                         /* strtoull() itself would accept space/+/- */
-                        if (*e >= '0' && *e <= '9') {
+                        if (ascii_isdigit(*e)) {
                                 unsigned long long l2;
                                 char *e2;
 
@@ -599,7 +599,7 @@ int parse_fractional_part_u(const char **p, size_t digits, unsigned *res) {
 
         /* accept any number of digits, strtoull is limited to 19 */
         for (size_t i = 0; i < digits; i++,s++) {
-                if (*s < '0' || *s > '9') {
+                if (!ascii_isdigit(*s)) {
                         if (i == 0)
                                 return -EINVAL;
 

src/basic/socket-util.c

@@ -833,7 +833,7 @@ bool ifname_valid_full(const char *p, IfnameValidFlags flags) {
                 if (!ifname_valid_char(*t))
                         return false;
 
-                numeric = numeric && (*t >= '0' && *t <= '9');
+                numeric = numeric && ascii_isdigit(*t);
         }
 
         /* It's fully numeric but didn't parse as valid ifindex above? if so, it must be too large or zero or

src/basic/terminal-util.c

@@ -624,7 +624,7 @@ int vtnr_from_tty(const char *tty) {
         if (!startswith(tty, "tty") )
                 return -EINVAL;
 
-        if (tty[3] < '0' || tty[3] > '9')
+        if (!ascii_isdigit(tty[3]))
                 return -EINVAL;
 
         r = safe_atoi(tty+3, &i);

src/basic/time-util.c

@@ -1411,9 +1411,8 @@ int verify_timezone(const char *name, int log_level) {
                 return -EINVAL;
 
         for (p = name; *p; p++) {
-                if (!(*p >= '0' && *p <= '9') &&
-                    !(*p >= 'a' && *p <= 'z') &&
-                    !(*p >= 'A' && *p <= 'Z') &&
+                if (!ascii_isdigit(*p) &&
+                    !ascii_isalpha(*p) &&
                     !IN_SET(*p, '-', '_', '+', '/'))
                         return -EINVAL;
 

src/basic/user-util.c

@@ -814,15 +814,13 @@ bool valid_user_group_name(const char *u, ValidUserFlags flags) {
                  * Note that other systems are even more restrictive, and don't permit underscores or uppercase characters.
                  */
 
-                if (!(u[0] >= 'a' && u[0] <= 'z') &&
-                    !(u[0] >= 'A' && u[0] <= 'Z') &&
+                if (!ascii_isalpha(u[0]) &&
                     u[0] != '_')
                         return false;
 
                 for (i = u+1; *i; i++)
-                        if (!(*i >= 'a' && *i <= 'z') &&
-                            !(*i >= 'A' && *i <= 'Z') &&
-                            !(*i >= '0' && *i <= '9') &&
+                        if (!ascii_isalpha(*i) &&
+                            !ascii_isdigit(*i) &&
                             !IN_SET(*i, '_', '-'))
                                 return false;