slre: drop wrong "anchored" optimization

The regex '^a|b' means "does the string start with a, or does it have
a b anywhere", not "does the string start with a or b" (the latter
should be spelled '^[ab]' or '^(a|b)'). It should match exactly the
same strings as 'b|^a'. But the current implementation hard-codes an
assumption that when the regex starts with a ^, the whole regex must
match from the beginning, i.e. it only attempts at offset 0.

It really should be completely symmetrical to 'b|c$' ("does it have a
b anywhere or end with c?"), which is treated correctly.

Another quirk is that currently the regex 'x*$', which should match
all strings (because it just means "does the string end
with 0 or more x'es"), does not, because in the unanchored case we
never attempt to match at ofs==len. In the anchored case, '^x*$', this
works correctly and matches exactly strings (including the empty
string) consisting entirely of x'es.

Fix both of these issues by dropping all use of the slre->anchored
member and always test at all possible offsets. If the regex does have
a ^ somewhere (including after a | branch character), that is
correctly handled by the match engine by only matching when *ofs is 0.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>

diff --git a/include/slre.h b/include/slre.h
index 4b41a4b276f8297358c44d1d512584628c304a29..af5b1302d9c9298e09a506ffef5afb6810de50cd 100644 (file)
--- a/include/slre.h
+++ b/include/slre.h
@@ -63,7 +63,6 @@ struct slre {
        int             code_size;
        int             data_size;
        int             num_caps;       /* Number of bracket pairs      */
-       int             anchored;       /* Must match from string start */
        const char      *err_str;       /* Error string                 */
 };
 

diff --git a/lib/slre.c b/lib/slre.c
index 277a59a03a712321492ee2989acfc36630e9c554..4f455400d3a62aeb8af42497ac9f8ce0328f4fb5 100644 (file)
--- a/lib/slre.c
+++ b/lib/slre.c
@@ -413,10 +413,7 @@ int
 slre_compile(struct slre *r, const char *re)
 {
        r->err_str = NULL;
-       r->code_size = r->data_size = r->num_caps = r->anchored = 0;
-
-       if (*re == '^')
-               r->anchored++;
+       r->code_size = r->data_size = r->num_caps = 0;
 
        emit(r, OPEN);  /* This will capture what matches full RE */
        emit(r, 0);
@@ -650,13 +647,9 @@ slre_match(const struct slre *r, const char *buf, int len,
 {
        int     i, ofs = 0, res = 0;
 
-       if (r->anchored) {
+       for (i = 0; i <= len && res == 0; i++) {
+               ofs = i;
                res = match(r, 0, buf, len, &ofs, caps);
-       } else {
-               for (i = 0; i < len && res == 0; i++) {
-                       ofs = i;
-                       res = match(r, 0, buf, len, &ofs, caps);
-               }
        }
 
        return res;