X-Git-Url: http://git.draconx.ca/gitweb/cdecl99.git/blobdiff_plain/0a1c8a90e23304220f6602e98aba5f891a1350b2..HEAD:/t/rng.c

diff --git a/t/rng.c b/t/rng.c
index e442d99..63e0818 100644
--- a/t/rng.c
+++ b/t/rng.c
@@ -15,24 +15,25 @@
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
- * The RNG implementation is adapted from xoshiro256+ and splitmix64
- * by David Blackman and Sebastiano Vigna, originally distributed under
- * the Creative Commons Zero public domain dedication.
+ * The RNG implementation is adapted from xoshiro256+ by David Blackman
+ * and Sebastiano Vigna, originally distributed under the Creative Commons
+ * Zero public domain dedication.
  */
 
 #include <config.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <inttypes.h>
 #include <errno.h>
 #include <limits.h>
+#include <inttypes.h>
 
 #if !TEST_RNG_NO_EXTERNAL_API
 #  include "test.h"
 #endif
 
 #define B64(x) ((x) & 0xffffffffffffffffull)
+#define B32(x) ((x) & 0xffffffffu)
 
 struct test_rng {
 	unsigned long long state[4];
@@ -61,38 +62,51 @@ static unsigned long long xoshiro256p(unsigned long long *s)
 	return ret;
 }
 
-static unsigned long long splitmix64(unsigned long long *state)
+/*
+ * 32-bit random number generator for seed expansion.
+ *
+ * The output filter is from the public domain MurmurHash3 by Austin Appleby.
+ *
+ * The state is incremented by the fractional part of the golden ratio,
+ * i.e., floor( (sqrt(5)-1)/2 * 2**32 )
+ */
+static uint_least32_t splitmix32(uint_least32_t *state)
 {
-	unsigned long long z;
+	uint_least32_t z;
 
-	z = B64(*state += 0x9e3779b97f4a7c15ull);
-	z = B64((z ^ (z >> 30)) * 0xbf58476d1ce4e5b9ull);
-	z = B64((z ^ (z >> 27)) * 0x94d049bb133111ebull);
+	z = B32(*state += 0x9e3779b9);
+	z = B32((z ^ (z >> 16)) * 0x85ebca6b);
+	z = B32((z ^ (z >> 13)) * 0xc2b2ae35);
 
-	return z ^ (z >> 31);
+	return z ^ (z >> 16);
+}
+
+static uint_least64_t seed64(uint_least32_t *state)
+{
+	uint_least64_t x;
+
+	x = splitmix32(state);
+	return (x << 32) | splitmix32(state);
 }
 
 #if !TEST_RNG_NO_EXTERNAL_API
 struct test_rng *test_rng_alloc(const char *seed_str)
 {
-	unsigned long long seed;
-	uintmax_t limit, seed_val;
+	test_uintmax seed_val;
 	struct test_rng *rng;
+	uint_least32_t seed;
 
-	limit  = (uintmax_t)0xffffffff;
-	limit |= (limit << 16 << 16);
-
-	if (!test_strtoumax(&seed_val, seed_str, limit)) {
+	if (!test_strtoumax(&seed_val, seed_str, 0xffffffff)) {
 		print_error("%s: invalid seed", seed_str);
 		return NULL;
 	}
 	seed = seed_val;
 
 	rng = malloc_nofail(sizeof *rng);
-	rng->state[0] = splitmix64(&seed);
-	rng->state[1] = splitmix64(&seed);
-	rng->state[2] = splitmix64(&seed);
-	rng->state[3] = splitmix64(&seed);
+	rng->state[0] = seed64(&seed);
+	rng->state[1] = seed64(&seed);
+	rng->state[2] = seed64(&seed);
+	rng->state[3] = seed64(&seed);
 
 	return rng;
 }