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>
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 @@
 		// 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 @@
 			// 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 @@
 				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; \
 	}