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97a5e3453a
Suppose I try the following:
struct int_node *node = node_pointer(node_alloc(1));
node->n = 5;
treap_insert(&root, node);
printf("%d\n", node->n);
Usually the result will be 5. But since treap_insert draws memory
from the node pool, if the caller is unlucky then (1) the node pool
will be full and (2) realloc will be forced to move the node pool to
find room, so the node address becomes invalid and the result of
dereferencing it is undefined.
So we ought to use offsets in preference to pointers for references
that would remain valid after a call to treap_insert. Tweak the
signature to hint at a certain special case: since the inserted node
can change address (though not offset), as a convenience teach
treap_insert to return its new address.
So the motivational example could be fixed by adding "node =".
struct int_node *node = node_pointer(node_alloc(1));
node->n = 5;
node = treap_insert(&root, node);
printf("%d\n", node->n);
Based on a true story.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
71 lines
1.7 KiB
C
71 lines
1.7 KiB
C
/*
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* test-treap.c: code to exercise the svn importer's treap structure
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*/
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#include "cache.h"
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#include "vcs-svn/obj_pool.h"
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#include "vcs-svn/trp.h"
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struct int_node {
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uintmax_t n;
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struct trp_node children;
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};
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obj_pool_gen(node, struct int_node, 3)
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static int node_cmp(struct int_node *a, struct int_node *b)
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{
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return (a->n > b->n) - (a->n < b->n);
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}
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trp_gen(static, treap_, struct int_node, children, node, node_cmp)
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static void strtonode(struct int_node *item, const char *s)
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{
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char *end;
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item->n = strtoumax(s, &end, 10);
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if (*s == '\0' || (*end != '\n' && *end != '\0'))
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die("invalid integer: %s", s);
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}
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int main(int argc, char *argv[])
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{
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struct strbuf sb = STRBUF_INIT;
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struct trp_root root = { ~0 };
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uint32_t item;
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if (argc != 1)
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usage("test-treap < ints");
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while (strbuf_getline(&sb, stdin, '\n') != EOF) {
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struct int_node *node = node_pointer(node_alloc(1));
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item = node_offset(node);
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strtonode(node, sb.buf);
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node = treap_insert(&root, node_pointer(item));
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if (node_offset(node) != item)
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die("inserted %"PRIu32" in place of %"PRIu32"",
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node_offset(node), item);
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}
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item = node_offset(treap_first(&root));
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while (~item) {
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uint32_t next;
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struct int_node *tmp = node_pointer(node_alloc(1));
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tmp->n = node_pointer(item)->n;
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next = node_offset(treap_next(&root, node_pointer(item)));
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treap_remove(&root, node_pointer(item));
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item = node_offset(treap_nsearch(&root, tmp));
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if (item != next && (!~item || node_pointer(item)->n != tmp->n))
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die("found %"PRIuMAX" in place of %"PRIuMAX"",
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~item ? node_pointer(item)->n : ~(uintmax_t) 0,
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~next ? node_pointer(next)->n : ~(uintmax_t) 0);
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printf("%"PRIuMAX"\n", tmp->n);
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}
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node_reset();
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return 0;
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}
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