thodg/libgit2

diff --git a/COPYING b/COPYING
index efeff14..ccfb7db 100644
--- a/COPYING
+++ b/COPYING
@@ -1132,3 +1132,15 @@ STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 OF THE POSSIBILITY OF SUCH DAMAGE.
 
+----------------------------------------------------------------------
+
+The xoroshiro256** implementation is licensed in the public domain:
+
+Written in 2018 by David Blackman and Sebastiano Vigna (vigna@acm.org)
+
+To the extent possible under law, the author has dedicated all copyright
+and related and neighboring rights to this software to the public domain
+worldwide. This software is distributed without any warranty.
+
+See <http://creativecommons.org/publicdomain/zero/1.0/>.
+
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index e2da4bc..e7b54d0 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -55,6 +55,8 @@ check_prototype_definition(qsort_r
 
 check_function_exists(qsort_s GIT_QSORT_S)
 
+check_function_exists(getentropy GIT_RAND_GETENTROPY)
+
 # Find required dependencies
 
 if(WIN32)
diff --git a/src/features.h.in b/src/features.h.in
index 81a8ae0..f920135 100644
--- a/src/features.h.in
+++ b/src/features.h.in
@@ -48,4 +48,6 @@
 #cmakedefine GIT_SHA1_OPENSSL 1
 #cmakedefine GIT_SHA1_MBEDTLS 1
 
+#cmakedefine GIT_RAND_GETENTROPY 1
+
 #endif
diff --git a/src/libgit2.c b/src/libgit2.c
index b3a72de..b17485d 100644
--- a/src/libgit2.c
+++ b/src/libgit2.c
@@ -20,6 +20,7 @@
 #include "mwindow.h"
 #include "object.h"
 #include "odb.h"
+#include "rand.h"
 #include "refs.h"
 #include "runtime.h"
 #include "sysdir.h"
@@ -70,6 +71,7 @@ int git_libgit2_init(void)
 		git_allocator_global_init,
 		git_threadstate_global_init,
 		git_threads_global_init,
+		git_rand_global_init,
 		git_hash_global_init,
 		git_sysdir_global_init,
 		git_filter_global_init,
diff --git a/src/rand.c b/src/rand.c
new file mode 100644
index 0000000..0a20813
--- /dev/null
+++ b/src/rand.c
@@ -0,0 +1,226 @@
+/*  Written in 2018 by David Blackman and Sebastiano Vigna (vigna@acm.org)
+
+To the extent possible under law, the author has dedicated all copyright
+and related and neighboring rights to this software to the public domain
+worldwide. This software is distributed without any warranty.
+
+See <http://creativecommons.org/publicdomain/zero/1.0/>. */
+
+#include "common.h"
+#include "rand.h"
+#include "runtime.h"
+
+#if defined(GIT_RAND_GETENTROPY)
+# include <sys/random.h>
+#endif
+
+static uint64_t state[4];
+static git_mutex state_lock;
+
+typedef union {
+	double f;
+	uint64_t d;
+} bits;
+
+#if defined(GIT_WIN32)
+GIT_INLINE(int) getseed(uint64_t *seed)
+{
+	HCRYPTPROV provider;
+	SYSTEMTIME systemtime;
+	FILETIME filetime, idletime, kerneltime, usertime;
+	bits convert;
+
+	if (CryptAcquireContext(&provider, 0, 0, PROV_RSA_FULL,
+	                        CRYPT_VERIFYCONTEXT|CRYPT_SILENT)) {
+		BOOL success = CryptGenRandom(provider, sizeof(uint64_t), (void *)seed);
+		CryptReleaseContext(provider, 0);
+
+		if (success)
+			return 0;
+	}
+
+	GetSystemTime(&systemtime);
+	if (!SystemTimeToFileTime(&systemtime, &filetime)) {
+		git_error_set(GIT_ERROR_OS, "could not get time for random seed");
+		return -1;
+	}
+
+	/* Fall-through: generate a seed from the time and system state */
+	*seed = 0;
+	*seed |= ((uint64_t)filetime.dwLowDateTime << 32);
+	*seed |= ((uint64_t)filetime.dwHighDateTime);
+
+	GetSystemTimes(&idletime, &kerneltime, &usertime);
+
+	*seed ^= ((uint64_t)idletime.dwLowDateTime << 32);
+	*seed ^= ((uint64_t)kerneltime.dwLowDateTime);
+	*seed ^= ((uint64_t)usertime.dwLowDateTime << 32);
+
+	*seed ^= ((uint64_t)idletime.dwHighDateTime);
+	*seed ^= ((uint64_t)kerneltime.dwHighDateTime << 12);
+	*seed ^= ((uint64_t)usertime.dwHighDateTime << 24);
+
+	*seed ^= ((uint64_t)GetCurrentProcessId() << 32);
+	*seed ^= ((uint64_t)GetCurrentThreadId() << 48);
+
+	convert.f = git__timer(); *seed ^= (convert.d);
+
+	/* Mix in the addresses of some functions and variables */
+	*seed ^= (((uint64_t)((uintptr_t)seed) << 32));
+	*seed ^= (((uint64_t)((uintptr_t)&errno)));
+
+	return 0;
+}
+
+#else
+
+GIT_INLINE(int) getseed(uint64_t *seed)
+{
+	struct timeval tv;
+	double loadavg[3];
+	bits convert;
+	int fd;
+
+# if defined(GIT_RAND_GETENTROPY)
+	GIT_UNUSED((fd = 0));
+
+	if (getentropy(seed, sizeof(uint64_t)) == 0)
+		return 0;
+# else
+	/*
+	 * Try to read from /dev/urandom; most modern systems will have
+	 * this, but we may be chrooted, etc, so it's not a fatal error
+	 */
+	if ((fd = open("/dev/urandom", O_RDONLY)) >= 0) {
+		ssize_t ret = read(fd, seed, sizeof(uint64_t));
+		close(fd);
+
+		if (ret == (ssize_t)sizeof(uint64_t))
+			return 0;
+	}
+# endif
+
+	/* Fall-through: generate a seed from the time and system state */
+	if (gettimeofday(&tv, NULL) < 0) {
+		git_error_set(GIT_ERROR_OS, "could get time for random seed");
+		return -1;
+	}
+
+	getloadavg(loadavg, 3);
+
+	*seed = 0;
+	*seed |= ((uint64_t)tv.tv_usec << 40);
+	*seed |= ((uint64_t)tv.tv_sec);
+
+	*seed ^= ((uint64_t)getpid() << 48);
+	*seed ^= ((uint64_t)getppid() << 32);
+	*seed ^= ((uint64_t)getpgid(0) << 28);
+	*seed ^= ((uint64_t)getsid(0) << 16);
+	*seed ^= ((uint64_t)getuid() << 8);
+	*seed ^= ((uint64_t)getgid());
+
+	convert.f = loadavg[0]; *seed ^= (convert.d >> 36);
+	convert.f = loadavg[1]; *seed ^= (convert.d);
+	convert.f = loadavg[2]; *seed ^= (convert.d >> 16);
+
+	convert.f = git__timer(); *seed ^= (convert.d);
+
+	/* Mix in the addresses of some variables */
+	*seed ^= ((uint64_t)((size_t)((void *)seed)) << 32);
+	*seed ^= ((uint64_t)((size_t)((void *)&errno)));
+
+	return 0;
+}
+#endif
+
+static void git_rand_global_shutdown(void)
+{
+	git_mutex_free(&state_lock);
+}
+
+int git_rand_global_init(void)
+{
+	uint64_t seed = 0;
+
+	if (git_mutex_init(&state_lock) < 0 || getseed(&seed) < 0)
+		return -1;
+
+	if (!seed) {
+		git_error_set(GIT_ERROR_INTERNAL, "failed to generate random seed");
+		return -1;
+	}
+
+	git_rand_seed(seed);
+	git_runtime_shutdown_register(git_rand_global_shutdown);
+
+	return 0;
+}
+
+/*
+ * This is splitmix64. xoroshiro256** uses 256 bit seed; this is used
+ * to generate 256 bits of seed from the given 64, per the author's
+ * recommendation.
+ */
+GIT_INLINE(uint64_t) splitmix64(uint64_t *in)
+{
+	uint64_t z;
+
+	*in += 0x9e3779b97f4a7c15;
+
+	z = *in;
+	z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
+	z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
+	return z ^ (z >> 31);
+}
+
+void git_rand_seed(uint64_t seed)
+{
+	uint64_t mixer;
+
+	mixer = seed;
+
+	git_mutex_lock(&state_lock);
+	state[0] = splitmix64(&mixer);
+	state[1] = splitmix64(&mixer);
+	state[2] = splitmix64(&mixer);
+	state[3] = splitmix64(&mixer);
+	git_mutex_unlock(&state_lock);
+}
+
+/* This is xoshiro256** 1.0, one of our all-purpose, rock-solid
+   generators. It has excellent (sub-ns) speed, a state (256 bits) that is
+   large enough for any parallel application, and it passes all tests we
+   are aware of.
+
+   For generating just floating-point numbers, xoshiro256+ is even faster.
+
+   The state must be seeded so that it is not everywhere zero. If you have
+   a 64-bit seed, we suggest to seed a splitmix64 generator and use its
+   output to fill s. */
+
+GIT_INLINE(uint64_t) rotl(const uint64_t x, int k) {
+	return (x << k) | (x >> (64 - k));
+}
+
+uint64_t git_rand_next(void) {
+	uint64_t t, result;
+
+	git_mutex_lock(&state_lock);
+
+	result = rotl(state[1] * 5, 7) * 9;
+
+	t = state[1] << 17;
+
+	state[2] ^= state[0];
+	state[3] ^= state[1];
+	state[1] ^= state[2];
+	state[0] ^= state[3];
+
+	state[2] ^= t;
+
+	state[3] = rotl(state[3], 45);
+
+	git_mutex_unlock(&state_lock);
+
+	return result;
+}
diff --git a/src/rand.h b/src/rand.h
new file mode 100644
index 0000000..2e60561
--- /dev/null
+++ b/src/rand.h
@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_rand_h__
+#define INCLUDE_rand_h__
+
+#include "common.h"
+
+/**
+ * Initialize the random number generation subsystem.  This will
+ * seed the random number generator with the system's entropy pool,
+ * if available, and will fall back to the current time and
+ * system information if not.
+ */
+int git_rand_global_init(void);
+
+/**
+ * Seed the pseudo-random number generator.  This is not needed to be
+ * called; the PRNG is seeded by `git_rand_global_init`, but it may
+ * be useful for testing.  When the same seed is specified, the same
+ * sequence of random numbers from `git_rand_next` is emitted.
+ *
+ * @param seed the seed to use
+ */
+void git_rand_seed(uint64_t seed);
+
+/**
+ * Get the next pseudo-random number in the sequence.
+ *
+ * @return a 64-bit pseudo-random number
+ */
+uint64_t git_rand_next(void);
+
+#endif