tweak: add xorshift example

C/scratchpad/makefile

@@ -0,0 +1,2 @@
+build: 
+	gcc xorshift.c -o xorshift

C/scratchpad/xorshift.c

@@ -0,0 +1,35 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+struct xorshift32_state {
+    uint32_t a;
+};
+
+uint32_t xorshift32(struct xorshift32_state *state)
+{
+	/* Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs" */
+	uint32_t x = state->a;
+	x ^= x << 13;
+	x ^= x >> 17;
+	x ^= x << 5;
+	return state->a = x;
+}
+
+int main(){
+	struct xorshift32_state** state = malloc(sizeof(struct xorshift32_state*) * 4);
+	for(int i=0; i<4;i++){
+		state[i] = malloc(sizeof(struct xorshift32_state));
+		state[i]->a = (uint32_t) i + 1;
+	}
+
+	printf("%i\n", xorshift32(state[0]));
+	printf("%i\n", xorshift32(state[0]));
+	for(int i=0; i<4;i++){
+		free(state[i]);
+	}
+	free(state);
+
+
+  return 0;
+}