From c32cf709b2e51924f8f1f91693febc1856fedc43 Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Fri, 21 Jun 2013 20:11:19 +0200
Subject: [PATCH] eliminate the right stack; work with the HInputStream
directly
---
src/backends/glr.c | 15 ++++----
src/backends/lr.c | 87 +++++++++++++++++++++++-----------------------
src/backends/lr.h | 12 +++----
3 files changed, 54 insertions(+), 60 deletions(-)
diff --git a/src/backends/glr.c b/src/backends/glr.c
index d460e8af..7a5f8f51 100644
--- a/src/backends/glr.c
+++ b/src/backends/glr.c
@@ -29,15 +29,14 @@ HLREngine *fork_engine(const HLREngine *engine)
HLREngine *eng2 = h_arena_malloc(engine->tarena, sizeof(HLREngine));
eng2->table = engine->table;
eng2->state = engine->state;
+ eng2->input = engine->input;
- // shallow-copy the stacks
+ // shallow-copy the stack
// this works because h_slist_push and h_slist_pop never modify
// the underlying structure of HSlistNodes, only the head pointer.
// in fact, this gives us prefix sharing for free.
- eng2->left = h_arena_malloc(engine->tarena, sizeof(HSlist));
- eng2->right = h_arena_malloc(engine->tarena, sizeof(HSlist));
- *eng2->left = *engine->left;
- *eng2->right = *engine->right;
+ eng2->stack = h_arena_malloc(engine->tarena, sizeof(HSlist));
+ *eng2->stack = *engine->stack;
eng2->arena = engine->arena;
eng2->tarena = engine->tarena;
@@ -54,7 +53,7 @@ HParseResult *h_glr_parse(HAllocator* mm__, const HParser* parser, HInputStream*
HArena *tarena = h_new_arena(mm__, 0); // tmp, deleted after parse
HSlist *engines = h_slist_new(tarena);
- h_slist_push(engines, h_lrengine_new(arena, tarena, table));
+ h_slist_push(engines, h_lrengine_new(arena, tarena, table, stream));
HParseResult *result = NULL;
while(result == NULL && !h_slist_empty(engines)) {
@@ -75,7 +74,7 @@ HParseResult *h_glr_parse(HAllocator* mm__, const HParser* parser, HInputStream*
continue;
}
- const HLRAction *action = h_lrengine_action(engine, stream);
+ const HLRAction *action = h_lrengine_action(engine);
// fork engine on conflicts
if(action && action->type == HLR_CONFLICT) {
@@ -120,8 +119,6 @@ HParserBackendVTable h__glr_backend_vtable = {
// XXX TODO
-// - eliminate right stack by always doing a shift after reduce
-// (shift should always follow reduce because rightmost)
// - split tables into
// - one mapping input bytes to actions (shift or reduce or conflict)
// - one mapping reduced-to lhs nonterminals to shift states
diff --git a/src/backends/lr.c b/src/backends/lr.c
index 2603ff2a..f33aab82 100644
--- a/src/backends/lr.c
+++ b/src/backends/lr.c
@@ -202,65 +202,64 @@ h_lr_lookup(const HLRTable *table, size_t state, const HCFChoice *symbol)
}
}
-HLREngine *h_lrengine_new(HArena *arena, HArena *tarena, const HLRTable *table)
+HLREngine *h_lrengine_new(HArena *arena, HArena *tarena, const HLRTable *table,
+ const HInputStream *stream)
{
HLREngine *engine = h_arena_malloc(tarena, sizeof(HLREngine));
engine->table = table;
engine->state = 0;
engine->run = true;
- engine->left = h_slist_new(tarena);
- engine->right = h_slist_new(tarena);
+ engine->stack = h_slist_new(tarena);
+ engine->input = *stream;
engine->arena = arena;
engine->tarena = tarena;
return engine;
}
-const HLRAction *h_lrengine_action(HLREngine *engine, HInputStream *stream)
+const HLRAction *h_lrengine_action(const HLREngine *engine)
{
- HSlist *right = engine->right;
- HArena *arena = engine->arena;
HArena *tarena = engine->tarena;
- // make sure there is input on the right stack
- if(h_slist_empty(right)) {
- // XXX use statically-allocated terminal symbols
- HCFChoice *x = h_arena_malloc(tarena, sizeof(HCFChoice));
- HParsedToken *v;
-
- uint8_t c = h_read_bits(stream, 8, false);
+ // XXX use statically-allocated terminal symbols
+ HCFChoice *x = h_arena_malloc(tarena, sizeof(HCFChoice));
- if(stream->overrun) { // end of input
- x->type = HCF_END;
- v = NULL;
- } else {
- x->type = HCF_CHAR;
- x->chr = c;
- v = h_arena_malloc(arena, sizeof(HParsedToken));
- v->token_type = TT_UINT;
- v->uint = c;
- }
+ HInputStream lookahead = engine->input;
+ uint8_t c = h_read_bits(&lookahead, 8, false);
- h_slist_push(right, v);
- h_slist_push(right, x);
+ if(lookahead.overrun) { // end of input
+ x->type = HCF_END;
+ } else {
+ x->type = HCF_CHAR;
+ x->chr = c;
}
- // peek at input symbol on the right side
- HCFChoice *symbol = right->head->elem;
+ return h_lr_lookup(engine->table, engine->state, x);
+}
+
+static HParsedToken *consume_input(HLREngine *engine)
+{
+ HParsedToken *v;
- // table lookup
- const HLRAction *action = h_lr_lookup(engine->table, engine->state, symbol);
+ uint8_t c = h_read_bits(&engine->input, 8, false);
- return action;
+ if(engine->input.overrun) { // end of input
+ v = NULL;
+ } else {
+ v = h_arena_malloc(engine->arena, sizeof(HParsedToken));
+ v->token_type = TT_UINT;
+ v->uint = c;
+ }
+
+ return v;
}
// run LR parser for one round; returns false when finished
static bool h_lrengine_step_(HLREngine *engine, const HLRAction *action)
{
// short-hand names
- HSlist *left = engine->left;
- HSlist *right = engine->right;
+ HSlist *stack = engine->stack;
HArena *arena = engine->arena;
HArena *tarena = engine->tarena;
@@ -278,11 +277,11 @@ static bool h_lrengine_step_(HLREngine *engine, const HLRAction *action)
value->token_type = TT_SEQUENCE;
value->seq = h_carray_new_sized(arena, len);
- // pull values off the left stack, rewinding state accordingly
+ // pull values off the stack, rewinding state accordingly
HParsedToken *v = NULL;
for(size_t i=0; i<len; i++) {
- v = h_slist_drop(left);
- engine->state = (uintptr_t)h_slist_drop(left);
+ v = h_slist_drop(stack);
+ engine->state = (uintptr_t)h_slist_drop(stack);
// collect values in result sequence
value->seq->elements[len-1-i] = v;
@@ -315,17 +314,17 @@ static bool h_lrengine_step_(HLREngine *engine, const HLRAction *action)
assert(shift->type == HLR_SHIFT);
// piggy-back the shift right here, never touching the input
- h_slist_push(left, (void *)(uintptr_t)engine->state);
- h_slist_push(left, value);
+ h_slist_push(stack, (void *)(uintptr_t)engine->state);
+ h_slist_push(stack, value);
engine->state = shift->nextstate;
if(symbol == engine->table->start)
return false; // reduced to start symbol; accept!
} else {
assert(action->type == HLR_SHIFT);
- h_slist_push(left, (void *)(uintptr_t)engine->state);
- h_slist_drop(right); // symbol (discard)
- h_slist_push(left, h_slist_drop(right)); // semantic value
+ HParsedToken *value = consume_input(engine);
+ h_slist_push(stack, (void *)(uintptr_t)engine->state);
+ h_slist_push(stack, value);
engine->state = action->nextstate;
}
@@ -341,9 +340,9 @@ void h_lrengine_step(HLREngine *engine, const HLRAction *action)
HParseResult *h_lrengine_result(HLREngine *engine)
{
// parsing was successful iff after a shift the engine is back in state 0
- if(engine->state == 0 && !h_slist_empty(engine->left)) {
+ if(engine->state == 0 && !h_slist_empty(engine->stack)) {
// on top of the stack is the start symbol's semantic value
- HParsedToken *tok = engine->left->head->elem;
+ HParsedToken *tok = engine->stack->head->elem;
return make_result(engine->arena, tok);
} else {
return NULL;
@@ -358,11 +357,11 @@ HParseResult *h_lr_parse(HAllocator* mm__, const HParser* parser, HInputStream*
HArena *arena = h_new_arena(mm__, 0); // will hold the results
HArena *tarena = h_new_arena(mm__, 0); // tmp, deleted after parse
- HLREngine *engine = h_lrengine_new(arena, tarena, table);
+ HLREngine *engine = h_lrengine_new(arena, tarena, table, stream);
// iterate engine to completion
while(engine->run)
- h_lrengine_step(engine, h_lrengine_action(engine, stream));
+ h_lrengine_step(engine, h_lrengine_action(engine));
HParseResult *result = h_lrengine_result(engine);
if(!result)
diff --git a/src/backends/lr.h b/src/backends/lr.h
index 5e2f0329..f76bd33f 100644
--- a/src/backends/lr.h
+++ b/src/backends/lr.h
@@ -70,11 +70,8 @@ typedef struct HLREngine_ {
size_t state;
bool run;
- // stack layout:
- // on the left stack, we put pairs: (saved state, semantic value)
- // on the right stack, we put pairs: (symbol, semantic value)
- HSlist *left; // left stack; reductions happen here
- HSlist *right; // right stack; input appears here
+ HSlist *stack; // holds pairs: (saved state, semantic value)
+ HInputStream input;
HArena *arena; // will hold the results
HArena *tarena; // tmp, deleted after parse
@@ -108,7 +105,8 @@ HLRItem *h_lritem_new(HArena *a, HCFChoice *lhs, HCFChoice **rhs, size_t mark);
HLRState *h_lrstate_new(HArena *arena);
HLRTable *h_lrtable_new(HAllocator *mm__, size_t nrows);
void h_lrtable_free(HLRTable *table);
-HLREngine *h_lrengine_new(HArena *arena, HArena *tarena, const HLRTable *table);
+HLREngine *h_lrengine_new(HArena *arena, HArena *tarena, const HLRTable *table,
+ const HInputStream *stream);
HLRAction *h_reduce_action(HArena *arena, const HLRItem *item);
HLRAction *h_shift_action(HArena *arena, size_t nextstate);
HLRAction *h_lr_conflict(HArena *arena, HLRAction *action, HLRAction *new);
@@ -128,7 +126,7 @@ int h_lalr_compile(HAllocator* mm__, HParser* parser, const void* params);
void h_lalr_free(HParser *parser);
const HLRAction *h_lr_lookup(const HLRTable *table, size_t state, const HCFChoice *symbol);
-const HLRAction *h_lrengine_action(HLREngine *engine, HInputStream *stream);
+const HLRAction *h_lrengine_action(const HLREngine *engine);
void h_lrengine_step(HLREngine *engine, const HLRAction *action);
HParseResult *h_lrengine_result(HLREngine *engine);
HParseResult *h_lr_parse(HAllocator* mm__, const HParser* parser, HInputStream* stream);
--
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