the same. */
restore_pos(aTHX_ prog);
}
+ if (prog->paren_names)
+ (void)hv_iterinit(prog->paren_names);
/* make sure $`, $&, $', and $digit will work later */
if ( !(flags & REXEC_NOT_FIRST) ) {
/*
- - regmatch - main matching routine
- *
- * Conceptually the strategy is simple: check to see whether the current
- * node matches, call self recursively to see whether the rest matches,
- * and then act accordingly. In practice we make some effort to avoid
- * recursion, in particular by going through "ordinary" nodes (that don't
- * need to know whether the rest of the match failed) by a loop instead of
- * by recursion.
- */
-/* [lwall] I've hoisted the register declarations to the outer block in order to
- * maybe save a little bit of pushing and popping on the stack. It also takes
- * advantage of machines that use a register save mask on subroutine entry.
- *
- * This function used to be heavily recursive, but since this had the
- * effect of blowing the CPU stack on complex regexes, it has been
- * restructured to be iterative, and to save state onto the heap rather
- * than the stack. Essentially whereever regmatch() used to be called, it
- * pushes the current state, notes where to return, then jumps back into
- * the main loop.
- *
- * Originally the structure of this function used to look something like
- S_regmatch() {
- int a = 1, b = 2;
+regmatch() - main matching routine
+
+This is basically one big switch statement in a loop. We execute an op,
+set 'next' to point the next op, and continue. If we come to a point which
+we may need to backtrack to on failure such as (A|B|C), we push a
+backtrack state onto the backtrack stack. On failure, we pop the top
+state, and re-enter the loop at the state indicated. If there are no more
+states to pop, we return failure.
+
+Sometimes we also need to backtrack on success; for example /A+/, where
+after successfully matching one A, we need to go back and try to
+match another one; similarly for lookahead assertions: if the assertion
+completes successfully, we backtrack to the state just before the assertion
+and then carry on. In these cases, the pushed state is marked as
+'backtrack on success too'. This marking is in fact done by a chain of
+pointers, each pointing to the previous 'yes' state. On success, we pop to
+the nearest yes state, discarding any intermediate failure-only states.
+Sometimes a yes state is pushed just to force some cleanup code to be
+called at the end of a successful match or submatch; e.g. (??{$re}) uses
+it to free the inner regex.
+
+Note that failure backtracking rewinds the cursor position, while
+success backtracking leaves it alone.
+
+A pattern is complete when the END op is executed, while a subpattern
+such as (?=foo) is complete when the SUCCESS op is executed. Both of these
+ops trigger the "pop to last yes state if any, otherwise return true"
+behaviour.
+
+A common convention in this function is to use A and B to refer to the two
+subpatterns (or to the first nodes thereof) in patterns like /A*B/: so A is
+the subpattern to be matched possibly multiple times, while B is the entire
+rest of the pattern. Variable and state names reflect this convention.
+
+The states in the main switch are the union of ops and failure/success of
+substates associated with with that op. For example, IFMATCH is the op
+that does lookahead assertions /(?=A)B/ and so the IFMATCH state means
+'execute IFMATCH'; while IFMATCH_A is a state saying that we have just
+successfully matched A and IFMATCH_A_fail is a state saying that we have
+just failed to match A. Resume states always come in pairs. The backtrack
+state we push is marked as 'IFMATCH_A', but when that is popped, we resume
+at IFMATCH_A or IFMATCH_A_fail, depending on whether we are backtracking
+on success or failure.
+
+The struct that holds a backtracking state is actually a big union, with
+one variant for each major type of op. The variable st points to the
+top-most backtrack struct. To make the code clearer, within each
+block of code we #define ST to alias the relevant union.
+
+Here's a concrete example of a (vastly oversimplified) IFMATCH
+implementation:
+
+ switch (state) {
+ ....
+
+#define ST st->u.ifmatch
+
+ case IFMATCH: // we are executing the IFMATCH op, (?=A)B
+ ST.foo = ...; // some state we wish to save
...
- while (scan != NULL) {
- a++; // do stuff with a and b
- ...
- switch (OP(scan)) {
- case FOO: {
- int local = 3;
- ...
- if (regmatch(...)) // recurse
- goto yes;
- }
- ...
- }
- }
- yes:
- return 1;
- }
+ // push a yes backtrack state with a resume value of
+ // IFMATCH_A/IFMATCH_A_fail, then continue execution at the
+ // first node of A:
+ PUSH_YES_STATE_GOTO(IFMATCH_A, A);
+ // NOTREACHED
+
+ case IFMATCH_A: // we have successfully executed A; now continue with B
+ next = B;
+ bar = ST.foo; // do something with the preserved value
+ break;
+
+ case IFMATCH_A_fail: // A failed, so the assertion failed
+ ...; // do some housekeeping, then ...
+ sayNO; // propagate the failure
+
+#undef ST
- * Now it looks something like this:
+ ...
+ }
- typedef struct {
- int a, b, local;
- int resume_state;
- } regmatch_state;
+For any old-timers reading this who are familiar with the old recursive
+approach, the code above is equivalent to:
- S_regmatch() {
- regmatch_state *st = new();
- int depth=0;
- st->a++; // do stuff with a and b
+ case IFMATCH: // we are executing the IFMATCH op, (?=A)B
+ {
+ int foo = ...
...
- while (scan != NULL) {
- ...
- switch (OP(scan)) {
- case FOO: {
- st->local = 3;
- ...
- st->scan = scan;
- scan = ...;
- st->resume_state = resume_FOO;
- goto start_recurse; // recurse
-
- resume_point_FOO:
- if (result)
- goto yes;
- }
- ...
- }
- start_recurse:
- st = new(); push a new state
- st->a = 1; st->b = 2;
- depth++;
- }
- yes:
- result = 1;
- if (depth--) {
- st = pop();
- switch (resume_state) {
- case resume_FOO:
- goto resume_point_FOO;
- ...
- }
+ if (regmatch(A)) {
+ next = B;
+ bar = foo;
+ break;
}
- return result
+ ...; // do some housekeeping, then ...
+ sayNO; // propagate the failure
}
-
- * WARNING: this means that any line in this function that contains a
- * REGMATCH() or TRYPAREN() is actually simulating a recursive call to
- * regmatch() using gotos instead. Thus the values of any local variables
- * not saved in the regmatch_state structure will have been lost when
- * execution resumes on the next line .
- *
- * States (ie the st pointer) are allocated in slabs of about 4K in size.
- * PL_regmatch_state always points to the currently active state, and
- * PL_regmatch_slab points to the slab currently containing PL_regmatch_state.
- * The first time regmatch is called, the first slab is allocated, and is
- * never freed until interpreter desctruction. When the slab is full,
- * a new one is allocated chained to the end. At exit from regmatch, slabs
- * allocated since entry are freed.
- */
+
+The topmost backtrack state, pointed to by st, is usually free. If you
+want to claim it, populate any ST.foo fields in it with values you wish to
+save, then do one of
+
+ PUSH_STATE_GOTO(resume_state, node);
+ PUSH_YES_STATE_GOTO(resume_state, node);
+
+which sets that backtrack state's resume value to 'resume_state', pushes a
+new free entry to the top of the backtrack stack, then goes to 'node'.
+On backtracking, the free slot is popped, and the saved state becomes the
+new free state. An ST.foo field in this new top state can be temporarily
+accessed to retrieve values, but once the main loop is re-entered, it
+becomes available for reuse.
+
+Note that the depth of the backtrack stack constantly increases during the
+left-to-right execution of the pattern, rather than going up and down with
+the pattern nesting. For example the stack is at its maximum at Z at the
+end of the pattern, rather than at X in the following:
+
+ /(((X)+)+)+....(Y)+....Z/
+
+The only exceptions to this are lookahead/behind assertions and the cut,
+(?>A), which pop all the backtrack states associated with A before
+continuing.
+
+Bascktrack state structs are allocated in slabs of about 4K in size.
+PL_regmatch_state and st always point to the currently active state,
+and PL_regmatch_slab points to the slab currently containing
+PL_regmatch_state. The first time regmatch() is called, the first slab is
+allocated, and is never freed until interpreter destruction. When the slab
+is full, a new one is allocated and chained to the end. At exit from
+regmatch(), slabs allocated since entry are freed.
+
+*/
#define DEBUG_STATE_pp(pp) \
locinput++;
nextchr = UCHARAT(locinput);
break;
+
+ case NREFFL:
+ {
+ char *s;
+ char type;
+ PL_reg_flags |= RF_tainted;
+ /* FALL THROUGH */
+ case NREF:
+ case NREFF:
+ type = OP(scan);
+ {
+ SV *sv_dat=(SV*)rex->data->data[ ARG( scan ) ];
+ I32 *nums=(I32*)SvPVX(sv_dat);
+ for ( n=0; n<SvIVX(sv_dat); n++ ) {
+ if ((I32)*PL_reglastparen >= nums[n] &&
+ PL_regstartp[nums[n]] != -1 &&
+ PL_regendp[nums[n]] != -1)
+ {
+ n = nums[n];
+ type = REF + ( type - NREF );
+ goto do_ref;
+ }
+ }
+ sayNO;
+ /* unreached */
+ }
case REFFL:
PL_reg_flags |= RF_tainted;
/* FALL THROUGH */
case REF:
- case REFF: {
- char *s;
+ case REFF:
n = ARG(scan); /* which paren pair */
+ type = OP(scan);
+ do_ref:
ln = PL_regstartp[n];
PL_reg_leftiter = PL_reg_maxiter; /* Void cache */
if ((I32)*PL_reglastparen < n || ln == -1)
break;
s = PL_bostr + ln;
- if (do_utf8 && OP(scan) != REF) { /* REF can do byte comparison */
+ if (do_utf8 && type != REF) { /* REF can do byte comparison */
char *l = locinput;
const char *e = PL_bostr + PL_regendp[n];
/*
* in the 8-bit case (no pun intended) because in Unicode we
* have to map both upper and title case to lower case.
*/
- if (OP(scan) == REFF) {
+ if (type == REFF) {
while (s < e) {
STRLEN ulen1, ulen2;
U8 tmpbuf1[UTF8_MAXBYTES_CASE+1];
/* Inline the first character, for speed. */
if (UCHARAT(s) != nextchr &&
- (OP(scan) == REF ||
- (UCHARAT(s) != ((OP(scan) == REFF
- ? PL_fold : PL_fold_locale)[nextchr]))))
+ (type == REF ||
+ (UCHARAT(s) != (type == REFF
+ ? PL_fold : PL_fold_locale)[nextchr])))
sayNO;
ln = PL_regendp[n] - ln;
if (locinput + ln > PL_regeol)
sayNO;
- if (ln > 1 && (OP(scan) == REF
+ if (ln > 1 && (type == REF
? memNE(s, locinput, ln)
- : (OP(scan) == REFF
+ : (type == REFF
? ibcmp(s, locinput, ln)
: ibcmp_locale(s, locinput, ln))))
sayNO;
locinput += ln;
nextchr = UCHARAT(locinput);
break;
- }
-
+ }
case NOTHING:
case TAIL:
break;
projects / p5sagit/p5-mst-13.2.git / blobdiff