Modify seed algorithm to use process ID, and use a few randomly selec…

…ted prime numbers that sort of look like words.

liblwgeom/cunit/cu_algorithm.c

@@ -1447,9 +1447,24 @@ static void test_point_density(void)
 
 	/* POLYGON */
 	geom = lwgeom_from_wkt("POLYGON((0 0,1 0,1 1,0 1,0 0))", LW_PARSER_CHECK_NONE);
-	mpt = lwgeom_to_points(geom, 100, 0); /* seed based on clock */
+	mpt = lwgeom_to_points(geom, 100, 0);  /* Set a zero seed to base it on Unix time and process ID */
 	CU_ASSERT_EQUAL(mpt->ngeoms,100);
+
+	/* Run a second time with a zero seed to get a different multipoint sequence */
+	mpt2 = lwgeom_to_points(geom, 100, 0);
+	eq = 0;
+	for (i = 0; i < 100; i++)
+	{
+		pt = (LWPOINT*)mpt->geoms[i];
+		pt2 = (LWPOINT*)mpt2->geoms[i];
+		if (lwpoint_get_x(pt) == lwpoint_get_x(pt2) && lwpoint_get_y(pt) == lwpoint_get_y(pt2))
+			eq++;
+	}
+	CU_ASSERT_EQUAL(eq, 0);
 	lwmpoint_free(mpt);
+	lwmpoint_free(mpt2);
+	pt = NULL;
+	pt2 = NULL;
 
 	/* Set seed to get a deterministic sequence */
 	mpt = lwgeom_to_points(geom, 1000, 12345);
@@ -1486,14 +1501,13 @@ static void test_point_density(void)
 
 
 	/* Check if the 1000th point is the expected value.
-	 * Note that if the PRNG is not portable, this test may fail
-	 */
+	 * Note that if the RNG is not portable, this test may fail. */
 	pt = (LWPOINT*)mpt->geoms[999];
 	// ewkt = lwgeom_to_ewkt((LWGEOM*)pt);
 	// printf("%s\n", ewkt);
 	// lwfree(ewkt);
-	CU_ASSERT_DOUBLE_EQUAL(lwpoint_get_x(pt), 0.179235638039549, 1e-11);
-	CU_ASSERT_DOUBLE_EQUAL(lwpoint_get_y(pt), 0.531253711538885, 1e-11);
+	CU_ASSERT_DOUBLE_EQUAL(lwpoint_get_x(pt), 0.801167838758, 1e-11);
+	CU_ASSERT_DOUBLE_EQUAL(lwpoint_get_y(pt), 0.345281131175, 1e-11);
 	lwmpoint_free(mpt);
 	pt = NULL;
 

liblwgeom/lwgeom_geos.c

@@ -1498,7 +1498,10 @@ lwpoly_to_points(const LWPOLY* lwpoly, uint32_t npoints, int32_t seed)
 	/* Get an empty multi-point ready to return */
 	mpt = lwmpoint_construct_empty(srid, 0, 0);
 
-	/* Init random number generator. Zero means "no seed", so make one up. */
+	/* Initiate random number generator.
+	 * Repeatable numbers are generated with seed values >= 1.
+	 * When seed is zero and has not previously been set, it is based on
+	 * Unix time (seconds) and process ID. */
 	lwrandom_set_seed( seed );
 
 	/* Now we fill in an array of cells, and then shuffle that array, */
@@ -1514,7 +1517,7 @@ lwpoly_to_points(const LWPOLY* lwpoly, uint32_t npoints, int32_t seed)
 		}
 	}
 
-	/* Fisher--Yates shuffle */
+	/* Fisher-Yates shuffle */
 	n = sample_height * sample_width;
 	if (n > 1)
 	{

liblwgeom/lwrandom.c

@@ -29,34 +29,43 @@
 #include <stddef.h>
 #include <time.h>
 
+#ifdef _WIN32
+#include <process.h>
+#define getpid _getpid
+#else
+#include <unistd.h>
+#endif
 
 static unsigned char _lwrandom_seed_set = 0;
 static int32_t _lwrandom_seed[3] = {0x330e, 0xabcd, 0x1234};
 
 /*
  * Set seed for a random number generator.
- * A zero value uses clock as seed the first time only.
- */
+ * Repeatable numbers are generated with seed values >= 1.
+ * When seed is zero and has not previously been set, it is based on
+ * Unix time (seconds) and process ID. */
 void
 lwrandom_set_seed(int32_t seed)
 {
 	if (seed == 0)
 	{
 		if (_lwrandom_seed_set == 0)
-			seed = ((unsigned int)time(NULL) * 1996) << 8;
+			seed = (unsigned int)time(NULL) + (unsigned int)getpid() - 0xbadd;
 		else
 			return;
 	}
-
-	_lwrandom_seed[1] = (seed % 2147483562) + 1; /* value between 1 and 2147483562 */
-	_lwrandom_seed[2] = (((seed + 6) >> 12) % 2147483398) + 1; /* value between 1 and 2147483398 */
+	/* s1 value between 1 and 2147483562 */
+	_lwrandom_seed[1] = (((int64_t)seed + 0xfeed) % 2147483562) + 1;
+	/* s2 value between 1 and 2147483398 */
+	_lwrandom_seed[2] = ((((int64_t)seed + 0xdefeb) << 5) % 2147483398) + 1;
 	_lwrandom_seed_set = 1;
 }
 
 /* for low-level external debugging */
 void
 _lwrandom_set_seeds(int32_t s1, int32_t s2)
 {
+	/* _lwrandom_seed[0] not used */
 	_lwrandom_seed[1] = s1;
 	_lwrandom_seed[2] = s2;
 	_lwrandom_seed_set = 1;

regress/core/tickets.sql

@@ -1120,7 +1120,7 @@ FROM (SELECT 'POLYGON((0 0,1 0,1 1,0 1,0 0))'::geometry AS g) AS f;
 
 -- #4304
 SELECT '#4304', ST_Equals(ST_GeneratePoints(g, 1000, 12345), ST_GeneratePoints(g, 1000, 12345)),
-ST_Distance(ST_GeometryN(ST_GeneratePoints(g, 1000, 12345), 1000), ST_GeometryFromText('POINT(0.1792356 0.5312537)')) < 1e-7
+ST_Distance(ST_GeometryN(ST_GeneratePoints(g, 1000, 12345), 1000), ST_GeometryFromText('POINT(0.801167838758 0.345281131175)')) < 1e-11
 FROM (SELECT 'POLYGON((0 0,1 0,1 1,0 1,0 0))'::geometry AS g) AS f;