Function match

Source/Misc/lua/src/lua.c:14042–14117

static const char *match (MatchState *ms, const char *s, const char *p) {
init: /* using goto's to optimize tail recursion */
switch (*p) {
case '(': {  /* start capture */
if (*(p+1) == ')')  /* position capture? */
return start_capture(ms, s, p+2, CAP_POSITION);
else
return start_capture(ms, s, p+1, CAP_UNFINISHED);
}
case ')': {  /* end capture */
return end_capture(ms, s, p+1);
}
case L_ESC: {
switch (*(p+1)) {
case 'b': {  /* balanced string? */
s = matchbalance(ms, s, p+2);
if (s == NULL) return NULL;
p+=4; goto init;  /* else return match(ms, s, p+4); */
}
case 'f': {  /* frontier? */
const char *ep; char previous;
p += 2;
if (*p != '[')
luaL_error(ms->L, "missing " LUA_QL("[") " after "
LUA_QL("%%f") " in pattern");
ep = classend(ms, p);  /* points to what is next */
previous = (s == ms->src_init) ? '\0' : *(s-1);
if (matchbracketclass(uchar(previous), p, ep-1) ||
!matchbracketclass(uchar(*s), p, ep-1)) return NULL;
p=ep; goto init;  /* else return match(ms, s, ep); */
}
default: {
if (isdigit(uchar(*(p+1)))) {  /* capture results (%0-%9)? */
s = match_capture(ms, s, uchar(*(p+1)));
if (s == NULL) return NULL;
p+=2; goto init;  /* else return match(ms, s, p+2) */
}
goto dflt;  /* case default */
}
}
}
case '\0': {  /* end of pattern */
return s;  /* match succeeded */
}
case '$': {
if (*(p+1) == '\0')  /* is the `$' the last char in pattern? */
return (s == ms->src_end) ? s : NULL;  /* check end of string */
else goto dflt;
}
default: dflt: {  /* it is a pattern item */
const char *ep = classend(ms, p);  /* points to what is next */
int m = s<ms->src_end && singlematch(uchar(*s), p, ep);
switch (*ep) {
case '?': {  /* optional */
const char *res;
if (m && ((res=match(ms, s+1, ep+1)) != NULL))
return res;
p=ep+1; goto init;  /* else return match(ms, s, ep+1); */