libbb: introduce and use is_prefixed_with()

function                                             old     new   delta
is_prefixed_with                                       -      18     +18
complete_username                                     78      77      -1
man_main                                             737     735      -2
fsck_device                                          429     427      -2
unpack_ar_archive                                     80      76      -4
strip_unsafe_prefix                                  105     101      -4
singlemount                                         1054    1050      -4
rtc_adjtime_is_utc                                    90      86      -4
resolve_mount_spec                                    88      84      -4
parse_one_line                                      1029    1025      -4
parse_conf                                          1460    1456      -4
may_wakeup                                            83      79      -4
loadkmap_main                                        219     215      -4
get_irqs_from_stat                                   103      99      -4
get_header_cpio                                      913     909      -4
findfs_main                                           79      75      -4
fbsplash_main                                       1230    1226      -4
load_crontab                                         776     771      -5
expand_vars_to_list                                 1151    1146      -5
date_main                                            881     876      -5
skip_dev_pfx                                          30      24      -6
make_device                                         2199    2193      -6
complete_cmd_dir_file                                773     767      -6
run_applet_and_exit                                  715     708      -7
uudecode_main                                        321     313      -8
pwdx_main                                            197     189      -8
execute                                              568     560      -8
i2cdetect_main                                      1186    1176     -10
procps_scan                                         1242    1230     -12
procps_read_smaps                                   1017    1005     -12
process_module                                       746     734     -12
patch_main                                          1903    1891     -12
nfsmount                                            3572    3560     -12
stack_machine                                        126     112     -14
process_timer_stats                                  449     435     -14
match_fstype                                         111      97     -14
do_ipaddr                                           1344    1330     -14
open_list_and_close                                  359     343     -16
get_header_tar                                      1795    1779     -16
prepend_new_eth_table                                340     323     -17
fsck_main                                           1811    1794     -17
find_iface_state                                      56      38     -18
dnsd_main                                           1321    1303     -18
base_device                                          179     158     -21
find_keyword                                         104      82     -22
handle_incoming_and_exit                            2785    2762     -23
parse_and_put_prompt                                 774     746     -28
modinfo                                              347     317     -30
find_action                                          204     171     -33
update_passwd                                       1470    1436     -34
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/49 up/down: 18/-540)         Total: -522 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

9 files changed, 49 insertions, 33 deletions

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 54300bd..8fd8fd5 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -193,7 +193,7 @@ void lbb_prepare(const char *applet
 	if (argv[1]
 	 && !argv[2]
 	 && strcmp(argv[1], "--help") == 0
-	 && strncmp(applet, "busybox", 7) != 0
+	 && !is_prefixed_with(applet, "busybox")
 	) {
 		/* Special case. POSIX says "test --help"
 		 * should be no different from e.g. "test --foo".  */
@@ -673,7 +673,7 @@ static int busybox_main(char **argv)
 		return 0;
 	}
 
-	if (strncmp(argv[1], "--list", 6) == 0) {
+	if (is_prefixed_with(argv[1], "--list")) {
 		unsigned i = 0;
 		const char *a = applet_names;
 		dup2(1, 2);
@@ -778,7 +778,7 @@ void FAST_FUNC run_applet_and_exit(const char *name, char **argv)
 	int applet = find_applet_by_name(name);
 	if (applet >= 0)
 		run_applet_no_and_exit(applet, argv);
-	if (strncmp(name, "busybox", 7) == 0)
+	if (is_prefixed_with(name, "busybox"))
 		exit(busybox_main(argv));
 }
 
@@ -817,7 +817,7 @@ int main(int argc UNUSED_PARAM, char **argv)
 
 #if defined(SINGLE_APPLET_MAIN)
 	/* Only one applet is selected in .config */
-	if (argv[1] && strncmp(argv[0], "busybox", 7) == 0) {
+	if (argv[1] && is_prefixed_with(argv[0], "busybox")) {
 		/* "busybox <applet> <params>" should still work as expected */
 		argv++;
 	}
diff --git a/libbb/compare_string_array.c b/libbb/compare_string_array.c
index 4b10cc1..e24815a 100644
--- a/libbb/compare_string_array.c
+++ b/libbb/compare_string_array.c
@@ -5,6 +5,24 @@
 
 #include "libbb.h"
 
+char* FAST_FUNC is_prefixed_with(const char *string, const char *key)
+{
+#if 0	/* Two passes over key - probably slower */
+	int len = strlen(key);
+	if (strncmp(string, key, len) == 0)
+		return string + len;
+	return NULL;
+#else	/* Open-coded */
+	while (*key != '\0') {
+		if (*key != *string)
+			return NULL;
+		key++;
+		string++;
+	}
+	return (char*)string;
+#endif
+}
+
 /* returns the array index of the string */
 /* (index of first match is returned, or -1) */
 int FAST_FUNC index_in_str_array(const char *const string_array[], const char *key)
@@ -39,10 +57,9 @@ int FAST_FUNC index_in_strings(const char *strings, const char *key)
 int FAST_FUNC index_in_substr_array(const char *const string_array[], const char *key)
 {
 	int i;
-	int len = strlen(key);
-	if (len) {
+	if (key[0]) {
 		for (i = 0; string_array[i] != 0; i++) {
-			if (strncmp(string_array[i], key, len) == 0) {
+			if (is_prefixed_with(string_array[i], key)) {
 				return i;
 			}
 		}
diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index 249b401..a83e07c 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -681,7 +681,7 @@ static NOINLINE unsigned complete_username(const char *ud)
 	setpwent();
 	while ((pw = getpwent()) != NULL) {
 		/* Null usernames should result in all users as possible completions. */
-		if (/*!userlen || */ strncmp(ud, pw->pw_name, userlen) == 0) {
+		if (/* !ud[0] || */ is_prefixed_with(pw->pw_name, ud)) {
 			add_match(xasprintf("~%s/", pw->pw_name));
 		}
 	}
@@ -792,7 +792,7 @@ static NOINLINE unsigned complete_cmd_dir_file(const char *command, int type)
 			if (!pfind[0] && DOT_OR_DOTDOT(name_found))
 				continue;
 			/* match? */
-			if (strncmp(name_found, pfind, pf_len) != 0)
+			if (!is_prefixed_with(name_found, pfind))
 				continue; /* no */
 
 			found = concat_path_file(paths[i], name_found);
@@ -1879,15 +1879,16 @@ static void parse_and_put_prompt(const char *prmt_ptr)
 						cwd_buf = xrealloc_getcwd_or_warn(NULL);
 						if (!cwd_buf)
 							cwd_buf = (char *)bb_msg_unknown;
-						else {
+						else if (home_pwd_buf[0]) {
+							char *after_home_user;
+
 							/* /home/user[/something] -> ~[/something] */
-							l = strlen(home_pwd_buf);
-							if (l != 0
-							 && strncmp(home_pwd_buf, cwd_buf, l) == 0
-							 && (cwd_buf[l] == '/' || cwd_buf[l] == '\0')
+							after_home_user = is_prefixed_with(cwd_buf, home_pwd_buf);
+							if (after_home_user
+							 && (*after_home_user == '/' || *after_home_user == '\0')
 							) {
 								cwd_buf[0] = '~';
-								overlapping_strcpy(cwd_buf + 1, cwd_buf + l);
+								overlapping_strcpy(cwd_buf + 1, after_home_user);
 							}
 						}
 					}
diff --git a/libbb/match_fstype.c b/libbb/match_fstype.c
index 32c3d7f..b066b42 100644
--- a/libbb/match_fstype.c
+++ b/libbb/match_fstype.c
@@ -17,7 +17,6 @@
 int FAST_FUNC match_fstype(const struct mntent *mt, const char *t_fstype)
 {
 	int match = 1;
-	int len;
 
 	if (!t_fstype)
 		return match;
@@ -27,10 +26,10 @@ int FAST_FUNC match_fstype(const struct mntent *mt, const char *t_fstype)
 		t_fstype += 2;
 	}
 
-	len = strlen(mt->mnt_type);
 	while (1) {
-		if (strncmp(mt->mnt_type, t_fstype, len) == 0
-		 && (t_fstype[len] == '\0' || t_fstype[len] == ',')
+		char *after_mnt_type = is_prefixed_with(t_fstype, mt->mnt_type);
+		if (after_mnt_type
+		 && (*after_mnt_type == '\0' || *after_mnt_type == ',')
 		) {
 			return match;
 		}
diff --git a/libbb/procps.c b/libbb/procps.c
index 5b68d34..948b91e 100644
--- a/libbb/procps.c
+++ b/libbb/procps.c
@@ -205,11 +205,11 @@ int FAST_FUNC procps_read_smaps(pid_t pid, struct smaprec *total,
 		// Rss:                 nnn kB
 		// .....
 
-		char *tp = buf, *p;
+		char *tp, *p;
 
 #define SCAN(S, X) \
-		if (strncmp(tp, S, sizeof(S)-1) == 0) {              \
-			tp = skip_whitespace(tp + sizeof(S)-1);      \
+		if ((tp = is_prefixed_with(buf, S)) != NULL) {       \
+			tp = skip_whitespace(tp);                    \
 			total->X += currec.X = fast_strtoul_10(&tp); \
 			continue;                                    \
 		}
@@ -247,7 +247,7 @@ int FAST_FUNC procps_read_smaps(pid_t pid, struct smaprec *total,
 			// skipping "rw-s FILEOFS M:m INODE "
 			tp = skip_whitespace(skip_fields(tp, 4));
 			// filter out /dev/something (something != zero)
-			if (strncmp(tp, "/dev/", 5) != 0 || strcmp(tp, "/dev/zero\n") == 0) {
+			if (!is_prefixed_with(tp, "/dev/") || strcmp(tp, "/dev/zero\n") == 0) {
 				if (currec.smap_mode[1] == 'w') {
 					currec.mapped_rw = currec.smap_size;
 					total->mapped_rw += currec.smap_size;
@@ -497,8 +497,8 @@ procps_status_t* FAST_FUNC procps_scan(procps_status_t* sp, int flags)
 				while (fgets(buf, sizeof(buf), file)) {
 					char *tp;
 #define SCAN_TWO(str, name, statement) \
-	if (strncmp(buf, str, sizeof(str)-1) == 0) { \
-		tp = skip_whitespace(buf + sizeof(str)-1); \
+	if ((tp = is_prefixed_with(buf, str)) != NULL) { \
+		tp = skip_whitespace(tp); \
 		sscanf(tp, "%u", &sp->name); \
 		statement; \
 	}
diff --git a/libbb/rtc.c b/libbb/rtc.c
index 6d06d57..c4117ba 100644
--- a/libbb/rtc.c
+++ b/libbb/rtc.c
@@ -22,7 +22,7 @@ int FAST_FUNC rtc_adjtime_is_utc(void)
 		char buffer[128];
 
 		while (fgets(buffer, sizeof(buffer), f)) {
-			if (strncmp(buffer, "UTC", 3) == 0) {
+			if (is_prefixed_with(buffer, "UTC")) {
 				utc = 1;
 				break;
 			}
diff --git a/libbb/skip_whitespace.c b/libbb/skip_whitespace.c
index 8c7b674..b6cfbba 100644
--- a/libbb/skip_whitespace.c
+++ b/libbb/skip_whitespace.c
@@ -33,7 +33,7 @@ char* FAST_FUNC skip_non_whitespace(const char *s)
 
 char* FAST_FUNC skip_dev_pfx(const char *tty_name)
 {
-	if (strncmp(tty_name, "/dev/", 5) == 0)
+	if (is_prefixed_with(tty_name, "/dev/"))
 		tty_name += 5;
 	return (char*)tty_name;
 }
diff --git a/libbb/update_passwd.c b/libbb/update_passwd.c
index dc26ebd..a2004f4 100644
--- a/libbb/update_passwd.c
+++ b/libbb/update_passwd.c
@@ -84,7 +84,6 @@ int FAST_FUNC update_passwd(const char *filename,
 	char *fnamesfx;
 	char *sfx_char;
 	char *name_colon;
-	unsigned user_len;
 	int old_fd;
 	int new_fd;
 	int i;
@@ -108,7 +107,6 @@ int FAST_FUNC update_passwd(const char *filename,
 	fnamesfx = xasprintf("%s+", filename);
 	sfx_char = &fnamesfx[strlen(fnamesfx)-1];
 	name_colon = xasprintf("%s:", name ? name : "");
-	user_len = strlen(name_colon);
 
 	if (shadow)
 		old_fp = fopen(filename, "r+");
@@ -179,7 +177,7 @@ int FAST_FUNC update_passwd(const char *filename,
 			while (list) {
 				list++;
  next_list_element:
-				if (strncmp(list, member, member_len) == 0) {
+				if (is_prefixed_with(list, member)) {
 					char c;
 					changed_lines++;
 					c = list[member_len];
@@ -201,13 +199,14 @@ int FAST_FUNC update_passwd(const char *filename,
 			goto next;
 		}
 
-		if (strncmp(name_colon, line, user_len) != 0) {
+		cp = is_prefixed_with(line, name_colon);
+		if (!cp) {
 			fprintf(new_fp, "%s\n", line);
 			goto next;
 		}
 
 		/* We have a match with "name:"... */
-		cp = line + user_len; /* move past name: */
+		/* cp points past "name:" */
 
 #if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
 		if (member) {
diff --git a/libbb/xconnect.c b/libbb/xconnect.c
index 1c8bb2b..2a96e03 100644
--- a/libbb/xconnect.c
+++ b/libbb/xconnect.c
@@ -171,7 +171,7 @@ IF_NOT_FEATURE_IPV6(sa_family_t af = AF_INET;)
 	const char *cp;
 	struct addrinfo hint;
 
-	if (ENABLE_FEATURE_UNIX_LOCAL && strncmp(host, "local:", 6) == 0) {
+	if (ENABLE_FEATURE_UNIX_LOCAL && is_prefixed_with(host, "local:")) {
 		struct sockaddr_un *sun;
 
 		r = xzalloc(LSA_LEN_SIZE + sizeof(struct sockaddr_un));