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Fix hashing on lists containing self-references

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The hashing function was bounded, but with an accidental backtrack
so it could take time exponential in the intended bound.

Closes #1842
This commit is contained in:
Matthew Flatt 2017-10-16 09:19:05 -06:00
parent f24273d7ef
commit 2454fd6931
2 changed files with 15 additions and 10 deletions
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19
pkgs/racket-test-core/tests/racket/basic.rktl
View File

@ -2204,7 +2204,8 @@
[v (vector 5 6 7)]
[a (make-a 1 (make-a 2 3))]
[b (box (list 1 2 3))]
[fl (flvector 1.0 +nan.0 0.0)])
[fl (flvector 1.0 +nan.0 0.0)]
[cyclic-list (read (open-input-string "#2=(#1=(#2#) #2#)"))])
(test 0 hash-count h1)
@ -2225,11 +2226,12 @@
(hash-set! h1 (save v) 'vector)
(hash-set! h1 (save a) 'struct)
(hash-set! h1 (save an-ax) 'structx)
(hash-set! h1 (save b) 'box))])
(hash-set! h1 (save b) 'box)
(hash-set! h1 cyclic-list 'cyclic-list))])
(if reorder?
(begin
(puts2)
(test 6 hash-count h1)
(test 7 hash-count h1)
(puts1))
(begin
(puts1)
@ -2245,7 +2247,7 @@
(loop (add1 i))
(hash-remove! h1 i))))
(test 14 hash-count h1)
(test 15 hash-count h1)
(test 'list hash-ref h1 l)
(test 'list hash-ref h1 (list 1 2 3))
(test 'another-list hash-ref h1 (list 5 7))
@ -2265,6 +2267,7 @@
(test 'box hash-ref h1 #&(1 2 3))
(test 'char hash-ref h1 (integer->char 955))
(test 'flvector hash-ref h1 (flvector 1.0 +nan.0 0.0))
(test 'cyclic-list hash-ref h1 cyclic-list)
(test #t
andmap
(lambda (i)
@ -2283,13 +2286,15 @@
(,an-ax . structx)
(#\u3BB . char)
(#&(1 2 3) . box)
(,(flvector 1.0 +nan.0 0.0) . flvector)))
(,(flvector 1.0 +nan.0 0.0) . flvector)
(,cyclic-list . cyclic-list)))
(hash-remove! h1 (list 1 2 3))
(test 13 hash-count h1)
(test 14 hash-count h1)
(test 'not-there hash-ref h1 l (lambda () 'not-there))
(let ([c 0])
(hash-for-each h1 (lambda (k v) (set! c (add1 c))))
(test 13 'count c))
(test 14 'count c))
;; return the hash table:
h1))

6
racket/src/racket/src/hash.c
View File

@ -1555,10 +1555,10 @@ static uintptr_t equal_hash_key(Scheme_Object *o, uintptr_t k, Hash_Info *hi)
hi->depth += 2;
k = (k << 3) + k;
k += equal_hash_key(SCHEME_CAR(o), 0, hi);
/* If it's a list, don't count cdr direction as depth: */
if (scheme_is_list(o))
hi->depth -= 2;
o = SCHEME_CDR(o);
/* If it continues as a list, don't count cdr direction as depth: */
if (SCHEME_PAIRP(o) && scheme_is_list(o))
hi->depth -= 2;
break;
}
case scheme_mutable_pair_type: