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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>
237 lines
7 KiB
C
237 lines
7 KiB
C
/*
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* C macro implementation of treaps.
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*
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* Usage:
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* #include <stdint.h>
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* #include "trp.h"
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* trp_gen(...)
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*
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* Licensed under a two-clause BSD-style license.
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* See LICENSE for details.
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*/
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#ifndef TRP_H_
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#define TRP_H_
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#define MAYBE_UNUSED __attribute__((__unused__))
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/* Node structure. */
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struct trp_node {
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uint32_t trpn_left;
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uint32_t trpn_right;
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};
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/* Root structure. */
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struct trp_root {
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uint32_t trp_root;
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};
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/* Pointer/Offset conversion. */
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#define trpn_pointer(a_base, a_offset) (a_base##_pointer(a_offset))
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#define trpn_offset(a_base, a_pointer) (a_base##_offset(a_pointer))
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#define trpn_modify(a_base, a_offset) \
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do { \
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if ((a_offset) < a_base##_pool.committed) { \
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uint32_t old_offset = (a_offset);\
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(a_offset) = a_base##_alloc(1); \
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*trpn_pointer(a_base, a_offset) = \
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*trpn_pointer(a_base, old_offset); \
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} \
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} while (0)
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/* Left accessors. */
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#define trp_left_get(a_base, a_field, a_node) \
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(trpn_pointer(a_base, a_node)->a_field.trpn_left)
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#define trp_left_set(a_base, a_field, a_node, a_left) \
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do { \
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trpn_modify(a_base, a_node); \
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trp_left_get(a_base, a_field, a_node) = (a_left); \
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} while (0)
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/* Right accessors. */
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#define trp_right_get(a_base, a_field, a_node) \
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(trpn_pointer(a_base, a_node)->a_field.trpn_right)
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#define trp_right_set(a_base, a_field, a_node, a_right) \
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do { \
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trpn_modify(a_base, a_node); \
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trp_right_get(a_base, a_field, a_node) = (a_right); \
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} while (0)
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/*
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* Fibonacci hash function.
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* The multiplier is the nearest prime to (2^32 times (√5 - 1)/2).
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* See Knuth §6.4: volume 3, 3rd ed, p518.
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*/
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#define trpn_hash(a_node) (uint32_t) (2654435761u * (a_node))
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/* Priority accessors. */
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#define trp_prio_get(a_node) trpn_hash(a_node)
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/* Node initializer. */
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#define trp_node_new(a_base, a_field, a_node) \
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do { \
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trp_left_set(a_base, a_field, (a_node), ~0); \
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trp_right_set(a_base, a_field, (a_node), ~0); \
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} while (0)
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/* Internal utility macros. */
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#define trpn_first(a_base, a_field, a_root, r_node) \
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do { \
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(r_node) = (a_root); \
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if ((r_node) == ~0) \
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return NULL; \
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while (~trp_left_get(a_base, a_field, (r_node))) \
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(r_node) = trp_left_get(a_base, a_field, (r_node)); \
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} while (0)
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#define trpn_rotate_left(a_base, a_field, a_node, r_node) \
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do { \
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(r_node) = trp_right_get(a_base, a_field, (a_node)); \
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trp_right_set(a_base, a_field, (a_node), \
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trp_left_get(a_base, a_field, (r_node))); \
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trp_left_set(a_base, a_field, (r_node), (a_node)); \
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} while (0)
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#define trpn_rotate_right(a_base, a_field, a_node, r_node) \
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do { \
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(r_node) = trp_left_get(a_base, a_field, (a_node)); \
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trp_left_set(a_base, a_field, (a_node), \
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trp_right_get(a_base, a_field, (r_node))); \
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trp_right_set(a_base, a_field, (r_node), (a_node)); \
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} while (0)
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#define trp_gen(a_attr, a_pre, a_type, a_field, a_base, a_cmp) \
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a_attr a_type MAYBE_UNUSED *a_pre##first(struct trp_root *treap) \
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{ \
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uint32_t ret; \
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trpn_first(a_base, a_field, treap->trp_root, ret); \
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return trpn_pointer(a_base, ret); \
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} \
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a_attr a_type MAYBE_UNUSED *a_pre##next(struct trp_root *treap, a_type *node) \
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{ \
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uint32_t ret; \
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uint32_t offset = trpn_offset(a_base, node); \
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if (~trp_right_get(a_base, a_field, offset)) { \
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trpn_first(a_base, a_field, \
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trp_right_get(a_base, a_field, offset), ret); \
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} else { \
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uint32_t tnode = treap->trp_root; \
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ret = ~0; \
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while (1) { \
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int cmp = (a_cmp)(trpn_pointer(a_base, offset), \
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trpn_pointer(a_base, tnode)); \
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if (cmp < 0) { \
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ret = tnode; \
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tnode = trp_left_get(a_base, a_field, tnode); \
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} else if (cmp > 0) { \
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tnode = trp_right_get(a_base, a_field, tnode); \
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} else { \
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break; \
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} \
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} \
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} \
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return trpn_pointer(a_base, ret); \
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} \
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a_attr a_type MAYBE_UNUSED *a_pre##search(struct trp_root *treap, a_type *key) \
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{ \
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int cmp; \
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uint32_t ret = treap->trp_root; \
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while (~ret && (cmp = (a_cmp)(key, trpn_pointer(a_base, ret)))) { \
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if (cmp < 0) { \
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ret = trp_left_get(a_base, a_field, ret); \
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} else { \
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ret = trp_right_get(a_base, a_field, ret); \
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} \
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} \
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return trpn_pointer(a_base, ret); \
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} \
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a_attr a_type MAYBE_UNUSED *a_pre##nsearch(struct trp_root *treap, a_type *key) \
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{ \
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int cmp; \
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uint32_t ret = treap->trp_root; \
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while (~ret && (cmp = (a_cmp)(key, trpn_pointer(a_base, ret)))) { \
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if (cmp < 0) { \
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if (!~trp_left_get(a_base, a_field, ret)) \
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break; \
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ret = trp_left_get(a_base, a_field, ret); \
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} else { \
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ret = trp_right_get(a_base, a_field, ret); \
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} \
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} \
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return trpn_pointer(a_base, ret); \
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} \
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a_attr uint32_t MAYBE_UNUSED a_pre##insert_recurse(uint32_t cur_node, uint32_t ins_node) \
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{ \
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if (cur_node == ~0) { \
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return ins_node; \
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} else { \
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uint32_t ret; \
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int cmp = (a_cmp)(trpn_pointer(a_base, ins_node), \
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trpn_pointer(a_base, cur_node)); \
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if (cmp < 0) { \
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uint32_t left = a_pre##insert_recurse( \
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trp_left_get(a_base, a_field, cur_node), ins_node); \
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trp_left_set(a_base, a_field, cur_node, left); \
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if (trp_prio_get(left) < trp_prio_get(cur_node)) \
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trpn_rotate_right(a_base, a_field, cur_node, ret); \
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else \
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ret = cur_node; \
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} else { \
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uint32_t right = a_pre##insert_recurse( \
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trp_right_get(a_base, a_field, cur_node), ins_node); \
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trp_right_set(a_base, a_field, cur_node, right); \
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if (trp_prio_get(right) < trp_prio_get(cur_node)) \
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trpn_rotate_left(a_base, a_field, cur_node, ret); \
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else \
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ret = cur_node; \
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} \
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return ret; \
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} \
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} \
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a_attr a_type *MAYBE_UNUSED a_pre##insert(struct trp_root *treap, a_type *node) \
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{ \
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uint32_t offset = trpn_offset(a_base, node); \
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trp_node_new(a_base, a_field, offset); \
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treap->trp_root = a_pre##insert_recurse(treap->trp_root, offset); \
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return trpn_pointer(a_base, offset); \
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} \
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a_attr uint32_t MAYBE_UNUSED a_pre##remove_recurse(uint32_t cur_node, uint32_t rem_node) \
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{ \
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int cmp = a_cmp(trpn_pointer(a_base, rem_node), \
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trpn_pointer(a_base, cur_node)); \
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if (cmp == 0) { \
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uint32_t ret; \
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uint32_t left = trp_left_get(a_base, a_field, cur_node); \
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uint32_t right = trp_right_get(a_base, a_field, cur_node); \
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if (left == ~0) { \
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if (right == ~0) \
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return ~0; \
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} else if (right == ~0 || trp_prio_get(left) < trp_prio_get(right)) { \
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trpn_rotate_right(a_base, a_field, cur_node, ret); \
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right = a_pre##remove_recurse(cur_node, rem_node); \
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trp_right_set(a_base, a_field, ret, right); \
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return ret; \
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} \
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trpn_rotate_left(a_base, a_field, cur_node, ret); \
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left = a_pre##remove_recurse(cur_node, rem_node); \
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trp_left_set(a_base, a_field, ret, left); \
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return ret; \
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} else if (cmp < 0) { \
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uint32_t left = a_pre##remove_recurse( \
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trp_left_get(a_base, a_field, cur_node), rem_node); \
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trp_left_set(a_base, a_field, cur_node, left); \
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return cur_node; \
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} else { \
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uint32_t right = a_pre##remove_recurse( \
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trp_right_get(a_base, a_field, cur_node), rem_node); \
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trp_right_set(a_base, a_field, cur_node, right); \
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return cur_node; \
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} \
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} \
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a_attr void MAYBE_UNUSED a_pre##remove(struct trp_root *treap, a_type *node) \
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{ \
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treap->trp_root = a_pre##remove_recurse(treap->trp_root, \
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trpn_offset(a_base, node)); \
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} \
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#endif
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