Use type-pun to avoid memcpy in building morton key (Closes #3871)

Fix from Komzpa at https://github.com/postgis/postgis/pull/144

git-svn-id: http://svn.osgeo.org/postgis/trunk@15875 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/liblwgeom/g_serialized.c b/liblwgeom/g_serialized.c
index 05acb9655e9f04a18d7db192362c6c1a80570409..54a8df3ecd286cea47791041863c5e620a6c2aa2 100644 (file)
--- a/liblwgeom/g_serialized.c
+++ b/liblwgeom/g_serialized.c
@@ -243,8 +243,14 @@ static uint64_t uint32_interleave_2(uint32_t u1, uint32_t u2)
 
 uint64_t gbox_get_sortable_hash(const GBOX *g)
 {
-       uint32_t ux, uy;
-       float fx, fy;
+       union x {
+               uint32_t u;
+               float f
+       };
+       union y {
+               uint32_t u;
+               float f
+       };
 
        /*
        * Since in theory the bitwise representation of an IEEE
@@ -261,19 +267,20 @@ uint64_t gbox_get_sortable_hash(const GBOX *g)
                p.z = (g->zmax + g->zmin) / 2.0;
                normalize(&p);
                cart2geog(&p, &gpt);
-               fx = gpt.lon;
-               fy = gpt.lat;
-               memcpy(&ux, &fx, sizeof(uint32_t));
-               memcpy(&uy, &fy, sizeof(uint32_t));
+               x.f = gpt.lon;
+               y.f = gpt.lat;
        }
        else
        {
-               fx = (g->xmax + g->xmin) / 2.0;
-               fy = (g->ymax + g->ymin) / 2.0;
-               memcpy(&ux, &fx, sizeof(uint32_t));
-               memcpy(&uy, &fy, sizeof(uint32_t));
+               /* 
+               * Here we'd like to get two ordinates from 4 in the box.
+               * Since it's just a sortable bit representation we can omit division from (A+B)/2.
+               * All it should do is subtract 1 from exponent anyways.
+               */
+               x.f = g->xmax + g->xmin;
+               y.f = g->ymax + g->ymin;
        }
-       return uint32_interleave_2(ux, uy);
+       return uint32_interleave_2(x.u, y.u);
 }
 
 int gserialized_cmp(const GSERIALIZED *g1, const GSERIALIZED *g2)
@@ -300,13 +307,13 @@ int gserialized_cmp(const GSERIALIZED *g1, const GSERIALIZED *g2)
 
        /* Empty == Empty */
        if (g1_is_empty && g2_is_empty)
-    {
-        /* POINT EMPTY == POINT EMPTY */
-        /* POINT EMPTY < LINESTRING EMPTY */
-        uint32_t t1 = gserialized_get_type(g1);
-        uint32_t t2 = gserialized_get_type(g2);
+       {
+               /* POINT EMPTY == POINT EMPTY */
+               /* POINT EMPTY < LINESTRING EMPTY */
+               uint32_t t1 = gserialized_get_type(g1);
+               uint32_t t2 = gserialized_get_type(g2);
                return t1 == t2 ? 0 : (t1 < t2 ? -1 : 1);
-    }
+       }
 
        /* Empty < Non-empty */
        if (g1_is_empty)
@@ -322,8 +329,8 @@ int gserialized_cmp(const GSERIALIZED *g1, const GSERIALIZED *g2)
                return 0;
 
        /* Using the centroids, calculate somewhat sortable */
-    /* hash key. The key doesn't provide good locality over */
-    /* the +/- boundary, but otherwise is pretty OK */
+       /* hash key. The key doesn't provide good locality over */
+       /* the +/- boundary, but otherwise is pretty OK */
        hash1 = gbox_get_sortable_hash(&box1);
        hash2 = gbox_get_sortable_hash(&box2);