From 23afea4b4e6fa00262c0b0cfbd958fa3e9e44093 Mon Sep 17 00:00:00 2001
From: "Sven M. Hallberg" <pesco@khjk.org>
Date: Sat, 22 Jun 2013 14:21:19 +0200
Subject: [PATCH] add demerge code path (untested)
---
src/backends/glr.c | 55 +++++++++++++++++++++++++++++++++++++++-------
src/backends/lr.c | 1 +
src/backends/lr.h | 3 ++-
3 files changed, 50 insertions(+), 9 deletions(-)
diff --git a/src/backends/glr.c b/src/backends/glr.c
index 2978e62d..411171b7 100644
--- a/src/backends/glr.c
+++ b/src/backends/glr.c
@@ -70,15 +70,54 @@ static const HLRAction *handle_conflict(HSlist *engines, const HLREngine *engine
return branches->head->elem;
}
-static HLREngine *handle_demerge(HSlist *engines, HLREngine *engine,
- const HLRAction *reduce)
+static HSlist *demerge_stack(HSlistNode *bottom, HSlistNode *mp, HSlist *stack)
{
- return engine; // XXX
+ HArena *arena = stack->arena;
+
+ HSlist *ret = h_slist_new(arena);
+
+ // copy the stack from the top
+ HSlistNode **y = &ret->head;
+ for(HSlistNode *x=stack->head; x && x!=mp; x=x->next) {
+ HSlistNode *node = h_arena_malloc(arena, sizeof(HSlistNode));
+ node->elem = x->elem;
+ node->next = NULL;
+ *y = node;
+ y = &node->next;
+ }
+ *y = bottom; // attach the ancestor stack
+
+ return ret;
+}
- for(size_t i=0; i<reduce->production.length; i++) {
- // XXX if stack hits bottom, demerge
+static void demerge(HSlist *engines, HLREngine *engine,
+ const HLRAction *action, size_t depth)
+{
+ // no-op on engines that are not merged
+ if(!engine->merged)
+ return;
+
+ HSlistNode *p = engine->stack->head;
+ for(size_t i=0; i<depth; i++) {
+ // if stack hits mergepoint, respawn ancestor
+ if(p == engine->mp) {
+ HLREngine *eng = engine->merged;
+ eng->stack = demerge_stack(eng->stack->head, engine->mp, engine->stack);
+ demerge(engines, eng, action, depth-i);
+
+ // call step and stow on restored ancestor
+ h_lrengine_step(eng, action);
+ stow_engine(engines, eng);
+ break;
+ }
+ p = p->next;
}
- // XXX call step and stow on the newly-created engines
+}
+
+static inline void
+handle_demerge(HSlist *engines, HLREngine *engine, const HLRAction *reduce)
+{
+ demerge(engines, engine, reduce, reduce->production.length);
}
HParseResult *h_glr_parse(HAllocator* mm__, const HParser* parser, HInputStream* stream)
@@ -119,8 +158,8 @@ HParseResult *h_glr_parse(HAllocator* mm__, const HParser* parser, HInputStream*
// fork engine on conflicts
action = handle_conflict(engines, engine, action->branches);
} else if(action->type == HLR_REDUCE) {
- // demerge as needed to ensure that stacks are deep enough
- engine = handle_demerge(engines, engine, action);
+ // demerge/respawn as needed
+ handle_demerge(engines, engine, action);
}
}
diff --git a/src/backends/lr.c b/src/backends/lr.c
index bb20f714..c481d291 100644
--- a/src/backends/lr.c
+++ b/src/backends/lr.c
@@ -210,6 +210,7 @@ HLREngine *h_lrengine_new(HArena *arena, HArena *tarena, const HLRTable *table,
engine->stack = h_slist_new(tarena);
engine->input = *stream;
engine->merged = NULL;
+ engine->mp = NULL;
engine->arena = arena;
engine->tarena = tarena;
diff --git a/src/backends/lr.h b/src/backends/lr.h
index 5febc247..ab486335 100644
--- a/src/backends/lr.h
+++ b/src/backends/lr.h
@@ -74,7 +74,8 @@ typedef struct HLREngine_ {
HSlist *stack; // holds pairs: (saved state, semantic value)
HInputStream input;
- HSlist *merged; // saved ancestor engines that merged to form this one
+ struct HLREngine_ *merged; // ancestor merged into this engine at mp
+ HSlistNode *mp; // mergepoint: stack->head at time of merge
HArena *arena; // will hold the results
HArena *tarena; // tmp, deleted after parse
--
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