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Avoid use of float arithmetic in bipartite_match.c.

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Since the distances used in this algorithm are small integers (not more
than the size of the U set, in fact), there is no good reason to use float
arithmetic for them.  Use short ints instead: they're smaller, faster, and
require no special portability assumptions.

Per testing by Greg Stark, which disclosed that the code got into an
infinite loop on VAX for lack of IEEE-style float infinities.  We don't
really care all that much whether Postgres can run on a VAX anymore,
but there seems sufficient reason to change this code anyway.

In passing, make a few other small adjustments to make the code match
usual Postgres coding style a bit better.
This commit is contained in:
Tom Lane
2015-08-23 13:02:13 -04:00
parent 5956b7f9e8
commit 44ed65a545
2 changed files with 55 additions and 36 deletions
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16
src/include/lib/bipartite_match.h
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@@ -11,7 +11,7 @@
/*
* Given a bipartite graph consisting of nodes U numbered 1..nU, nodes V
* numbered 1..nV, and an adjacency map of undirected edges in the form
* adjacency[u] = [n, v1, v2, v3, ... vn], we wish to find a "maximum
* adjacency[u] = [k, v1, v2, v3, ... vk], we wish to find a "maximum
* cardinality matching", which is defined as follows: a matching is a subset
* of the original edges such that no node has more than one edge, and a
* matching has maximum cardinality if there exists no other matching with a
@@ -24,21 +24,23 @@
* the problem of planning a collection of grouping sets with the provably
* minimal number of sort operations.
*/
typedef struct bipartite_match_state
typedef struct BipartiteMatchState
{
/* inputs: */
int u_size; /* size of U */
int v_size; /* size of V */
short **adjacency; /* adjacency[u] = [k, v1,v2,v3,...,vk] */
/* outputs: */
int matching; /* number of edges in matching */
short **adjacency; /* adjacency[u] = [n, v1,v2,v3,...,vn] */
short *pair_uv; /* pair_uv[u] -> v */
short *pair_vu; /* pair_vu[v] -> u */
float *distance; /* distance[u], float so we can have +inf */
/* private state for matching algorithm: */
short *distance; /* distance[u] */
short *queue; /* queue storage for breadth search */
} BipartiteMatchState;
BipartiteMatchState *BipartiteMatch(int u_size, int v_size, short **adjacency);
extern BipartiteMatchState *BipartiteMatch(int u_size, int v_size, short **adjacency);
void BipartiteMatchFree(BipartiteMatchState *state);
extern void BipartiteMatchFree(BipartiteMatchState *state);
#endif /* BIPARTITE_MATCH_H */