diff --git a/day11/Makefile b/day11/Makefile
index dcd6a88..dc3fdbf 100644
--- a/day11/Makefile
+++ b/day11/Makefile
@@ -20,7 +20,7 @@ all: part1 part2
 inpu%-sz.h: inpu%
 	echo "#define input_sz (`head -n 1 $< | wc -m`)" > $@
 
-inpu%.h: inpu% | input-sz.h
+inpu%.h: inpu% | inpu%-sz.h
 	@rm -f $@
 	while read line; do \
 		echo "\"$$line\"," >> $@; \
@@ -31,6 +31,9 @@ part1: day11.c | input.h
 	$(CC) $< $(CFLAGS) -o $@ $(LDFLAGS)
 	$(STRIP) $@
 
+part1-test: day11.c | input-test.h
+	$(CC) $< -DTEST $(CFLAGS) -o $@ $(LDFLAGS)
+	$(STRIP) $@
 clean:
-	rm -f input{,-sz}.h
-	rm -f part{1,2}
+	rm -f input{,-sz}{,-test}.h
+	rm -f part{1,2}{,-test}
diff --git a/day11/day11.c b/day11/day11.c
index 4e1144a..2034d6d 100644
--- a/day11/day11.c
+++ b/day11/day11.c
@@ -1,14 +1,25 @@
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include <panic.h>
 #include <attrs.h>
 
 const char* const input[] = {
+#ifdef TEST
+#include "input-test.h"
+#else
 #include "input.h"
+#endif
 };
 
 // input_sz //
+#ifdef TEST
+#include "input-test-sz.h"
+#else
 #include "input-sz.h"
+#endif
+
 #define INPUT_WIDTH (input_sz-1)
 #define INPUT_HEIGHT (sizeof(input)/sizeof(char*)) 
 
@@ -57,13 +68,100 @@ static inline void gol_set(gol_t* restrict gol, int x,int y, enum gol_state st)
 	gol->arena[GOL_INDEX(x,y)] = st;
 }
 
+static inline int count_states(const enum gol_state* state, enum gol_state s, size_t n)
+{
+	register int j=0;
+	for(register size_t i=0;i<n;i++)
+		j+= (state[i] == s);
+	return j;
+}
+
+static inline int gol_count(const gol_t* gol, enum gol_state s)
+{
+	return count_states(gol->arena, s, INPUT_WIDTH*INPUT_HEIGHT);
+}
+
+static inline void neighbours(const gol_t* gol, int x, int y, enum gol_state out[restrict 8])
+{
+	out[0] = gol_index(gol, x-1, y-1);
+	out[1] = gol_index(gol, x, y-1);
+	out[2] = gol_index(gol, x+1, y-1);
+
+	out[3] = gol_index(gol, x-1, y);
+	//out[4] = gol_index(gol, x, y);
+	out[4] = gol_index(gol, x+1, y);
+
+	out[5] = gol_index(gol, x-1, y+1);
+	out[6] = gol_index(gol, x, y+1);
+	out[7] = gol_index(gol, x+1, y+1);
+}
+
+static void simulate_ip(const gol_t* source, gol_t* restrict dest)
+{
+	for(size_t h=0;h<INPUT_HEIGHT;h++)
+		for(size_t w=0;w<INPUT_WIDTH;w++) {
+			enum gol_state next = gol_index(source, w, h);
+			enum gol_state n[8];
+			neighbours(source, w, h, n);
+			switch(next) {
+			case STATE_EMPTY:
+				if(count_states(n, STATE_OCCU, 8)==0) next = STATE_OCCU;
+				break;
+			case STATE_OCCU:
+				if(count_states(n, STATE_OCCU, 8)>=4) next = STATE_EMPTY;
+			default: break;
+			}
+			gol_set(dest, w, h, next);
+		}
+}
+
+static inline int gol_eq(const gol_t* g1, const gol_t* g2)
+{
+	return memcmp(g1->arena, g2->arena, sizeof(g1->arena))==0;
+}
+
+gol_t simulate_once(const gol_t* source)
+{
+	gol_t out = *source;
+	simulate_ip(source, &out);
+	
+	return out;
+}
+
+#ifdef DEBUG
+static void print_arena(const gol_t* gol)
+{
+	for(size_t h=0;h<INPUT_HEIGHT;h++) {
+		for(size_t w=0;w<INPUT_WIDTH;w++) fputc((char)gol_index(gol, w, h), stderr);
+		fputc('\n', stderr);
+	}
+}
+#endif
+
 int main()
 {
 	gol_t* arena = box(gol_t);
 	*arena = generate_arena();
 
-	printf("%lu\n", sizeof(arena));
-
+#ifdef DEBUG
+	printf("First: \n");
+	print_arena(arena);
+#endif
+	gol_t tmp;
+	while(1)
+	{
+		tmp = simulate_once(arena);
+#ifdef DEBUG
+		printf("Next: \n");
+		print_arena(&tmp);
+#endif
+		if(gol_eq(&tmp, arena))
+		{
+			printf("%d\n", gol_count(&tmp, STATE_OCCU));
+			break;
+		}
+		*arena = tmp;
+	}
 	free(arena);
 	return 0;
 }