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change sequence variants of first and derives_epsilon to take a

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null-terminated array
This commit is contained in:
Sven M. Hallberg 2013-04-30 20:16:16 +02:00
parent 73a84d17b8
commit 85aaf94332
1 changed files with 14 additions and 20 deletions
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34
src/backends/ll.c
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@ -126,13 +126,12 @@ bool h_symbol_derives_epsilon(HCFGrammar *g, const HCFChoice *symbol)
}
}
/* Does the sentential form given by s derive the empty string? */
bool h_sequence_derives_epsilon(HCFGrammar *g, const HCFSequence *s)
/* Does the sentential form s derive the empty string? s NULL-terminated. */
bool h_sequence_derives_epsilon(HCFGrammar *g, HCFChoice **s)
{
// return true iff all symbols in s derive epsilon
HCFChoice **x;
for(x = s->items; *x; x++) {
if(!h_symbol_derives_epsilon(g, *x))
for(; *s; s++) {
if(!h_symbol_derives_epsilon(g, *s))
return false;
}
return true;
@ -165,7 +164,7 @@ static void collect_geneps(HCFGrammar *g)
// this NT derives epsilon if any of its productions does.
HCFSequence **p;
for(p = symbol->seq; *p != NULL; p++) {
if(h_sequence_derives_epsilon(g, *p)) {
if(h_sequence_derives_epsilon(g, (*p)->items)) {
h_hashset_put(g->nts, symbol);
break;
}
@ -176,16 +175,11 @@ static void collect_geneps(HCFGrammar *g)
}
// helper
static HHashSet *first_sequence_(HCFGrammar *g, const HCFChoice **s);
/* Compute first set of sentential form s. s NULL-terminated. */
HHashSet *h_first_sequence(HCFGrammar *g, HCFChoice **s);
static inline HHashSet *h_first_sequence(HCFGrammar *g, const HCFSequence *s)
{
// why do I have to cast to a type that's _more_ const?
return first_sequence_(g, (const HCFChoice **)s->items);
}
static HHashSet *h_first_symbol(HCFGrammar *g, const HCFChoice *x)
/* Compute first set of symbol x. Memoized. */
HHashSet *h_first_symbol(HCFGrammar *g, const HCFChoice *x)
{
HHashSet *ret;
HCFSequence **p;
@ -218,7 +212,7 @@ static HHashSet *h_first_symbol(HCFGrammar *g, const HCFChoice *x)
// this is a nonterminal
// return the union of the first sets of all productions
for(p=x->seq; *p; ++p)
h_hashset_put_all(ret, h_first_sequence(g, *p));
h_hashset_put_all(ret, h_first_sequence(g, (*p)->items));
break;
default: // should not be reached
assert_message(0, "unknown HCFChoice type");
@ -227,7 +221,7 @@ static HHashSet *h_first_symbol(HCFGrammar *g, const HCFChoice *x)
return ret;
}
static HHashSet *first_sequence_(HCFGrammar *g, const HCFChoice **s)
HHashSet *h_first_sequence(HCFGrammar *g, HCFChoice **s)
{
// the first set of the empty sequence is empty
if(*s == NULL)
@ -236,13 +230,13 @@ static HHashSet *first_sequence_(HCFGrammar *g, const HCFChoice **s)
// first(X tail) = first(X) if X does not derive epsilon
// = first(X) u first(tail) otherwise
const HCFChoice *x = s[0];
const HCFChoice **tail = s+1;
HCFChoice *x = s[0];
HCFChoice **tail = s+1;
HHashSet *first_x = h_first_symbol(g, x);
if(h_symbol_derives_epsilon(g, x)) {
// return the union of first(x) and first(tail)
HHashSet *first_tail = first_sequence_(g, tail);
HHashSet *first_tail = h_first_sequence(g, tail);
HHashSet *ret = h_hashset_new(g->arena, h_eq_ptr, h_hash_ptr);
h_hashset_put_all(ret, first_x);
h_hashset_put_all(ret, first_tail);