libbb: code shrink and speed up index_in_strings()
Rewrite index_in_strings() to replace calls to strcmp()/strlen().
With this change searching for valid names in the applet_names
array (for example) is 40% faster.
The code has to assume the strings aren't sorted, so will always scan
the entire array when presented with an invalid name.
function old new delta
index_in_strings 63 56 -7
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-7) Total: -7 bytes
Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/compare_string_array.c b/libbb/compare_string_array.c
index a06e57d..d8cd033 100644
--- a/libbb/compare_string_array.c
+++ b/libbb/compare_string_array.c
@@ -63,13 +63,19 @@
int FAST_FUNC index_in_strings(const char *strings, const char *key)
{
- int idx = 0;
+ int j, idx = 0;
while (*strings) {
- if (strcmp(strings, key) == 0) {
- return idx;
+ /* Do we see "key\0" at current position in strings? */
+ for (j = 0; *strings == key[j]; ++j) {
+ if (*strings++ == '\0') {
+ //bb_error_msg("found:'%s' i:%u", key, idx);
+ return idx; /* yes */
+ }
}
- strings += strlen(strings) + 1; /* skip NUL */
+ /* No. Move to the start of the next string. */
+ while (*strings++ != '\0')
+ continue;
idx++;
}
return -1;