First commit

1 files changed, 64 insertions, 0 deletions

diff --git a/xorshift.c b/xorshift.c
new file mode 100644
index 0000000..6fdd5fb
--- /dev/null
+++ b/xorshift.c
@@ -0,0 +1,64 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <unistd.h>
+#include <assert.h>
+#include <limits.h>
+#include <sys/random.h>
+#include <string.h>
+#include "structs.h"
+
+struct rng_state global_rng_state;
+
+__attribute__((visibility("default"))) bool initialize_states(){
+	assert( (sizeof(uint32_t) * CHAR_BIT) == 32 );
+	memset( (void*)&global_rng_state, 0, sizeof(struct rng_state) );
+	ssize_t state_bytes_read = 0;
+	if ( (state_bytes_read = getrandom((void*)&global_rng_state.states, 16 * sizeof(uint32_t), GRND_NONBLOCK)) == -1 )
+		return false;
+	if ( (size_t)state_bytes_read < (16 * sizeof(uint32_t)) ){
+		errno = EIO;
+		return false;
+	}
+	global_rng_state.state_idx = global_rng_state.states[7] & 0x0f;
+	errno = 0;
+	return true;
+}
+
+__attribute__((visibility("default"))) uint32_t get_random_output(){
+	size_t use_state = global_rng_state.state_idx;
+	global_rng_state.state_idx = global_rng_state.states[use_state] & 0x0f;
+	if ( global_rng_state.gen_period_ctr >= 0xffffffff ){
+		global_rng_state.period_end_ctr++;
+		if ( global_rng_state.period_end_ctr >= 16 ){
+			assert( initialize_states() == true );
+			global_rng_state.period_end_ctr = 0;
+		}
+		global_rng_state.gen_period_ctr = 0;
+	}
+	global_rng_state.gen_period_ctr++;
+	global_rng_state.states[use_state] ^= global_rng_state.states[use_state] >> 11;
+	global_rng_state.states[use_state] ^= global_rng_state.states[use_state] << 7;
+	global_rng_state.states[use_state] ^= global_rng_state.states[use_state] >> 16;
+	return global_rng_state.states[use_state] * OUTPUT_MULTIPLIER;
+}
+
+__attribute__((visibility("default"))) uint32_t get_uniform_uint( uint32_t min, uint32_t max ){
+	if ( max <= min )
+		return min;
+	uint32_t ncount = (max - min) + 1;
+	uint32_t upper_bound = 0xffffffff - (0xffffffff % ncount);
+	uint32_t gen_output = get_random_output();
+	if ( gen_output > upper_bound ){
+		while ( gen_output > upper_bound )
+			gen_output = get_random_output();
+	}
+	return (gen_output % max) + min;
+}
+
+__attribute__((visibility("default"))) void clear_rng_state(){
+	memset( (void*)&global_rng_state, 0, sizeof(struct rng_state) );
+	return;
+}