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refactor h_llk_lookup to take the input stream as argument

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This commit is contained in:
Sven M. Hallberg 2013-05-20 21:28:16 +02:00
parent fb3aae7aec
commit 91c04314a4
1 changed files with 27 additions and 20 deletions
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47
src/backends/llk.c
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@ -19,8 +19,18 @@ typedef struct HLLkTable_ {
} HLLkTable;
/* Interface to look up an entry in the parse table. */
const HCFSequence *h_llk_lookup(const HLLkTable *table, const HCFChoice *x, HCFToken tok)
const HCFSequence *h_llk_lookup(const HLLkTable *table, const HCFChoice *x,
HInputStream lookahead)
{
// note the lookahead stream is passed by value, i.e. a copy
// reading bits from it does not consume them from the input
HCFToken tok;
uint8_t c = h_read_bits(&lookahead, 8, false);
if(lookahead.overrun)
tok = end_token;
else
tok = char_token(c);
const HHashTable *row = h_hashtable_get(table->rows, x);
assert(row != NULL); // the table should have one row for each nonterminal
@ -200,19 +210,8 @@ HParseResult *h_llk_parse(HAllocator* mm__, const HParser* parser, HInputStream*
// initialize with the start symbol on the stack.
h_slist_push(stack, table->start);
HCFToken lookahead = 0; // 0 = empty
// when we empty the stack, the parse is complete.
while(!h_slist_empty(stack)) {
// fill up lookahead buffer as required
if(lookahead == 0) {
uint8_t c = h_read_bits(stream, 8, false);
if(stream->overrun)
lookahead = end_token;
else
lookahead = char_token(c);
}
// pop top of stack for inspection
HCFChoice *x = h_slist_pop(stack);
assert(x != NULL);
@ -229,7 +228,7 @@ HParseResult *h_llk_parse(HAllocator* mm__, const HParser* parser, HInputStream*
seq = h_carray_new(arena);
// look up applicable production in parse table
const HCFSequence *p = h_llk_lookup(table, x, lookahead);
const HCFSequence *p = h_llk_lookup(table, x, *stream);
if(p == NULL)
goto no_parse;
@ -260,18 +259,17 @@ HParseResult *h_llk_parse(HAllocator* mm__, const HParser* parser, HInputStream*
// x is a terminal or simple charset; match against input
// consume the input token
HCFToken input = lookahead;
lookahead = 0;
uint8_t input = h_read_bits(stream, 8, false);
switch(x->type) {
case HCF_END:
if(input != end_token)
if(!stream->overrun)
goto no_parse;
tok = NULL;
break;
case HCF_CHAR:
if(input != char_token(x->chr))
if(input != x->chr)
goto no_parse;
tok = h_arena_malloc(arena, sizeof(HParsedToken));
tok->token_type = TT_UINT;
@ -279,13 +277,13 @@ HParseResult *h_llk_parse(HAllocator* mm__, const HParser* parser, HInputStream*
break;
case HCF_CHARSET:
if(input == end_token)
if(stream->overrun)
goto no_parse;
if(!charset_isset(x->charset, token_char(input)))
if(!charset_isset(x->charset, input))
goto no_parse;
tok = h_arena_malloc(arena, sizeof(HParsedToken));
tok->token_type = TT_UINT;
tok->uint = token_char(input);
tok->uint = input;
break;
default: // should not be reached
@ -338,6 +336,15 @@ HParserBackendVTable h__llk_backend_vtable = {
// dummy!
int test_llk(void)
{
/* for k=2:
S -> A | B
A -> X Y a
B -> Y b
X -> x | ''
Y -> y -- for k=3 use "yy"
*/
HParser *c = h_many(h_ch('x'));
HParser *q = h_sequence(c, h_ch('y'), NULL);
HParser *p = h_choice(q, h_end_p(), NULL);