Avoid use of float arithmetic in bipartite_match.c.

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.

diff --git a/src/backend/lib/bipartite_match.c b/src/backend/lib/bipartite_match.c
index 037dd1de30b828882abd0fdc21aaf2e0a15d228f..317222f57aceaf536c13ec002f5583a51dedf59f 100644 (file)
--- a/src/backend/lib/bipartite_match.c
+++ b/src/backend/lib/bipartite_match.c
@@ -16,17 +16,20 @@
  */
 #include "postgres.h"
 
-#include <float.h>
-#include <math.h>
 #include <limits.h>
 
 #include "lib/bipartite_match.h"
 #include "miscadmin.h"
-#include "utils/builtins.h"
 
+/*
+ * The distances computed in hk_breadth_search can easily be seen to never
+ * exceed u_size.  Since we restrict u_size to be less than SHRT_MAX, we
+ * can therefore use SHRT_MAX as the "infinity" distance needed as a marker.
+ */
+#define HK_INFINITY  SHRT_MAX
 
 static bool hk_breadth_search(BipartiteMatchState *state);
-static bool hk_depth_search(BipartiteMatchState *state, int u, int depth);
+static bool hk_depth_search(BipartiteMatchState *state, int u);
 
 /*
  * Given the size of U and V, where each is indexed 1..size, and an adjacency
@@ -37,26 +40,29 @@ BipartiteMatch(int u_size, int v_size, short **adjacency)
 {
    BipartiteMatchState *state = palloc(sizeof(BipartiteMatchState));
 
-   Assert(u_size < SHRT_MAX);
-   Assert(v_size < SHRT_MAX);
+   if (u_size < 0 || u_size >= SHRT_MAX ||
+       v_size < 0 || v_size >= SHRT_MAX)
+       elog(ERROR, "invalid set size for BipartiteMatch");
 
    state->u_size = u_size;
    state->v_size = v_size;
-   state->matching = 0;
    state->adjacency = adjacency;
-   state->pair_uv = palloc0((u_size + 1) * sizeof(short));
-   state->pair_vu = palloc0((v_size + 1) * sizeof(short));
-   state->distance = palloc((u_size + 1) * sizeof(float));
-   state->queue = palloc((u_size + 2) * sizeof(short));
+   state->matching = 0;
+   state->pair_uv = (short *) palloc0((u_size + 1) * sizeof(short));
+   state->pair_vu = (short *) palloc0((v_size + 1) * sizeof(short));
+   state->distance = (short *) palloc((u_size + 1) * sizeof(short));
+   state->queue = (short *) palloc((u_size + 2) * sizeof(short));
 
    while (hk_breadth_search(state))
    {
        int         u;
 
-       for (u = 1; u <= u_size; ++u)
+       for (u = 1; u <= u_size; u++)
+       {
            if (state->pair_uv[u] == 0)
-               if (hk_depth_search(state, u, 1))
+               if (hk_depth_search(state, u))
                    state->matching++;
+       }
 
        CHECK_FOR_INTERRUPTS(); /* just in case */
    }
@@ -79,19 +85,23 @@ BipartiteMatchFree(BipartiteMatchState *state)
    pfree(state);
 }
 
+/*
+ * Perform the breadth-first search step of H-K matching.
+ * Returns true if successful.
+ */
 static bool
 hk_breadth_search(BipartiteMatchState *state)
 {
    int         usize = state->u_size;
    short      *queue = state->queue;
-   float      *distance = state->distance;
+   short      *distance = state->distance;
    int         qhead = 0;      /* we never enqueue any node more than once */
    int         qtail = 0;      /* so don't have to worry about wrapping */
    int         u;
 
-   distance[0] = get_float4_infinity();
+   distance[0] = HK_INFINITY;
 
-   for (u = 1; u <= usize; ++u)
+   for (u = 1; u <= usize; u++)
    {
        if (state->pair_uv[u] == 0)
        {
@@ -99,7 +109,7 @@ hk_breadth_search(BipartiteMatchState *state)
            queue[qhead++] = u;
        }
        else
-           distance[u] = get_float4_infinity();
+           distance[u] = HK_INFINITY;
    }
 
    while (qtail < qhead)
@@ -111,45 +121,52 @@ hk_breadth_search(BipartiteMatchState *state)
            short      *u_adj = state->adjacency[u];
            int         i = u_adj ? u_adj[0] : 0;
 
-           for (; i > 0; --i)
+           for (; i > 0; i--)
            {
                int         u_next = state->pair_vu[u_adj[i]];
 
-               if (isinf(distance[u_next]))
+               if (distance[u_next] == HK_INFINITY)
                {
                    distance[u_next] = 1 + distance[u];
+                   Assert(qhead < usize + 2);
                    queue[qhead++] = u_next;
-                   Assert(qhead <= usize + 2);
                }
            }
        }
    }
 
-   return !isinf(distance[0]);
+   return (distance[0] != HK_INFINITY);
 }
 
+/*
+ * Perform the depth-first search step of H-K matching.
+ * Returns true if successful.
+ */
 static bool
-hk_depth_search(BipartiteMatchState *state, int u, int depth)
+hk_depth_search(BipartiteMatchState *state, int u)
 {
-   float      *distance = state->distance;
+   short      *distance = state->distance;
    short      *pair_uv = state->pair_uv;
    short      *pair_vu = state->pair_vu;
    short      *u_adj = state->adjacency[u];
    int         i = u_adj ? u_adj[0] : 0;
+   short       nextdist;
 
    if (u == 0)
        return true;
+   if (distance[u] == HK_INFINITY)
+       return false;
+   nextdist = distance[u] + 1;
 
-   if ((depth % 8) == 0)
-       check_stack_depth();
+   check_stack_depth();
 
-   for (; i > 0; --i)
+   for (; i > 0; i--)
    {
        int         v = u_adj[i];
 
-       if (distance[pair_vu[v]] == distance[u] + 1)
+       if (distance[pair_vu[v]] == nextdist)
        {
-           if (hk_depth_search(state, pair_vu[v], depth + 1))
+           if (hk_depth_search(state, pair_vu[v]))
            {
                pair_vu[v] = u;
                pair_uv[u] = v;
@@ -158,6 +175,6 @@ hk_depth_search(BipartiteMatchState *state, int u, int depth)
        }
    }
 
-   distance[u] = get_float4_infinity();
+   distance[u] = HK_INFINITY;
    return false;
 }

diff --git a/src/include/lib/bipartite_match.h b/src/include/lib/bipartite_match.h
index 373bbede1e1b1ca112008b0b64540628ae4ab829..c106a7e41d18c400a6ca06db857deb02776ef773 100644 (file)
--- a/src/include/lib/bipartite_match.h
+++ b/src/include/lib/bipartite_match.h
@@ -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 */