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ur: fixes "stack" overflow in preorder traversal, simplifies "stack"

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This commit is contained in:
Joe Bryan 2021-10-12 11:33:12 -04:00
parent 10b996e323
commit 9cb53597fb
1 changed files with 11 additions and 16 deletions
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27
pkg/urbit/ur/hashcons.c
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@ -937,7 +937,6 @@ struct ur_walk_fore_s {
ur_root_t *r; ur_root_t *r;
uint32_t prev; uint32_t prev;
uint32_t size; uint32_t size;
uint32_t fill;
ur_nref *top; ur_nref *top;
}; };
@ -950,7 +949,6 @@ ur_walk_fore_init_with(ur_root_t *r,
w->top = _oom("walk_fore", malloc(s_size * sizeof(*w->top))); w->top = _oom("walk_fore", malloc(s_size * sizeof(*w->top)));
w->prev = s_prev; w->prev = s_prev;
w->size = s_size; w->size = s_size;
w->fill = 0;
w->r = r; w->r = r;
return w; return w;
@ -969,45 +967,42 @@ ur_walk_fore_with(ur_walk_fore_t *w,
void (*atom)(ur_root_t*, ur_nref, void*), void (*atom)(ur_root_t*, ur_nref, void*),
ur_bool_t (*cell)(ur_root_t*, ur_nref, void*)) ur_bool_t (*cell)(ur_root_t*, ur_nref, void*))
{ {
ur_root_t *r = w->r; ur_root_t *r = w->r;
ur_nref *don = w->top; uint32_t fill = 1;
w->top += ++w->fill;
*w->top = ref; *w->top = ref;
while ( w->top != don ) { do {
// visit atom, pop stack // visit atom, pop stack
// //
if ( !ur_deep(ref) ) { if ( !ur_deep(ref) ) {
atom(r, ref, v); atom(r, ref, v);
w->top--; w->fill--; fill--;
} }
// visit cell, pop stack if false // visit cell, pop stack if false
// //
else if ( !cell(r, ref, v) ) { else if ( !cell(r, ref, v) ) {
w->top--; w->fill--; fill--;
} }
// push the tail, continue into the head // push the tail, continue into the head
// //
else { else {
*w->top = ur_tail(r, ref); w->top[fill++] = ur_tail(r, ref);
// reallocate "stack" if full // reallocate "stack" if full
// //
if ( w->size == w->fill ) { if ( w->size == fill ) {
uint32_t next = w->prev + w->size; uint32_t next = w->prev + w->size;
don = _oom("walk_fore", realloc(don, next * sizeof(*don))); w->top = _oom("walk_fore", realloc(w->top, next * sizeof(*w->top)));
w->top = don + w->fill;
w->prev = w->size; w->prev = w->size;
w->size = next; w->size = next;
} }
w->top++; w->fill++; w->top[fill] = ur_head(r, ref);
*w->top = ur_head(r, ref);
} }
ref = *w->top; ref = w->top[fill];
} } while ( fill );
} }
void void