Made state array size and shift value for state selection configurable

Now the state array size and the shift value for state selection are confirutable through the Makefile or through environment variables STATE_SIZE and SHIFT_VALUE

3 files changed, 11 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index 4ffc5a4..a91be1c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,13 +1,15 @@
 CC=gcc
 OUTPUT_MULTIPLIER=0x6ab64cc1
+STATE_SIZE=32U
+SHIFT_VALUE=27U
 
 rel:
 	mkdir -p ./build
-	$(CC) -Wall -Werror -pedantic -O2 -march=x86-64-v3 -mavx2 -std=gnu23 -DOUTPUT_MULTIPLIER=${OUTPUT_MULTIPLIER} -shared -fPIC ./xorshift.c -o ./build/libxorshift.so
+	$(CC) -Wall -Werror -pedantic -O2 -march=x86-64-v3 -mavx2 -std=gnu23 -DSHIFT_VALUE=${SHIFT_VALUE} -DSTATE_SIZE=${STATE_SIZE} -DOUTPUT_MULTIPLIER=${OUTPUT_MULTIPLIER} -shared -fPIC ./xorshift.c -o ./build/libxorshift.so
 
 debug:
 	mkdir -p ./build
-	$(CC) -Wall -Werror -pedantic -O2 -march=x86-64-v3 -mavx2 -std=gnu23 -ggdb -DOUTPUT_MULTIPLIER=${OUTPUT_MULTIPLIER} -shared -fPIC ./xorshift.c -o ./build/libxorshift.so
+	$(CC) -Wall -Werror -pedantic -O2 -march=x86-64-v3 -mavx2 -std=gnu23 -ggdb -DSHIFT_VALUE=${SHIFT_VALUE} -DSTATE_SIZE=${STATE_SIZE} -DOUTPUT_MULTIPLIER=${OUTPUT_MULTIPLIER} -shared -fPIC ./xorshift.c -o ./build/libxorshift.so
 
 clean:
 	rm -rf ./build
diff --git a/structs.h b/structs.h
index 34c923b..c39abeb 100644
--- a/structs.h
+++ b/structs.h
@@ -1,6 +1,6 @@
 struct rng_state{
 	size_t state_idx;
-	uint32_t states[16];
+	uint32_t states[STATE_SIZE];
 	uint32_t gen_period_ctr;
 	uint8_t period_end_ctr;
 };
diff --git a/xorshift.c b/xorshift.c
index ac4d087..528f3db 100644
--- a/xorshift.c
+++ b/xorshift.c
@@ -7,6 +7,7 @@
 #include <assert.h>
 #include <limits.h>
 #include <sys/random.h>
+#include <math.h>
 #include <string.h>
 #include "structs.h"
 
@@ -16,23 +17,23 @@ __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 )
+	if ( (state_bytes_read = getrandom((void*)&global_rng_state.states, STATE_SIZE * sizeof(uint32_t), GRND_NONBLOCK)) == -1 )
 		return false;
-	if ( (size_t)state_bytes_read < (16 * sizeof(uint32_t)) ){
+	if ( (size_t)state_bytes_read < (STATE_SIZE * sizeof(uint32_t)) ){
 		errno = EIO;
 		return false;
 	}
-	global_rng_state.state_idx = global_rng_state.states[7] >> 28;
+	global_rng_state.state_idx = global_rng_state.states[(uint32_t)(floor(STATE_SIZE / 2))] >> SHIFT_VALUE;
 	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] >> 28;
+	global_rng_state.state_idx = global_rng_state.states[use_state] >> SHIFT_VALUE;
 	if ( global_rng_state.gen_period_ctr >= 0xffffffff ){
 		global_rng_state.period_end_ctr++;
-		if ( global_rng_state.period_end_ctr >= 16 ){
+		if ( global_rng_state.period_end_ctr >= STATE_SIZE ){
 			assert( initialize_states() == true );
 			global_rng_state.period_end_ctr = 0;
 		}