diff --git a/Makefile b/Makefile
index c0ab356..9640eb2 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 all: $(patsubst %.cpp,%.elf,$(wildcard example/*.cpp))
 
-OPT = -Og
+OPT = -O3
 
 include dreamcast/base.mk
 include dreamcast/common.mk
diff --git a/aoc.mk b/aoc.mk
index c9ed242..cde2a6c 100644
--- a/aoc.mk
+++ b/aoc.mk
@@ -20,6 +20,10 @@ DREAMCAST_OBJ = \
 	$(LIB)/font/dejavusansmono/dejavusansmono.data.o \
 	$(LIB)/sh7091/serial.o \
 	$(LIB)/maple/maple.o
+#	libgcc/_divdi3.o \
+#	libgcc/_moddi3.o \
+#	libgcc/_udiv_qrnnd_16.o \
+#	libgcc/_clz.o
 
 include solutions.mk
 
diff --git a/day11/input.txt b/day11/input.txt
new file mode 100644
index 0000000..ca46e95
--- /dev/null
+++ b/day11/input.txt
@@ -0,0 +1 @@
+70949 6183 4 3825336 613971 0 15 182
diff --git a/day11/input.txt.h b/day11/input.txt.h
new file mode 100644
index 0000000..122c594
--- /dev/null
+++ b/day11/input.txt.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_day11_input_txt_start __asm("_binary_day11_input_txt_start");
+extern uint32_t _binary_day11_input_txt_end __asm("_binary_day11_input_txt_end");
+extern uint32_t _binary_day11_input_txt_size __asm("_binary_day11_input_txt_size");
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/day11/sample1.txt b/day11/sample1.txt
new file mode 100644
index 0000000..9b26c84
--- /dev/null
+++ b/day11/sample1.txt
@@ -0,0 +1 @@
+125 17
diff --git a/day11/sample1.txt.h b/day11/sample1.txt.h
new file mode 100644
index 0000000..eccd574
--- /dev/null
+++ b/day11/sample1.txt.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_day11_sample1_txt_start __asm("_binary_day11_sample1_txt_start");
+extern uint32_t _binary_day11_sample1_txt_end __asm("_binary_day11_sample1_txt_end");
+extern uint32_t _binary_day11_sample1_txt_size __asm("_binary_day11_sample1_txt_size");
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/day11/solution.c b/day11/solution.c
new file mode 100644
index 0000000..4e79e91
--- /dev/null
+++ b/day11/solution.c
@@ -0,0 +1,172 @@
+#include <stdint.h>
+
+#include "parse.h"
+#include "unparse.h"
+#include "printf.h"
+
+static void split_base10(int64_t n, int digits, int64_t * a, int64_t * b)
+{
+  int pow = 1;
+  digits /= 2;
+  while (digits-- > 0)
+    pow *= 10;
+  int64_t split = pow;
+  *a = n / split;
+  *b = n % split;
+}
+
+static int stone_rule(int64_t n, int64_t * a, int64_t * b)
+{
+  int digits;
+  if (n == 0) {
+    *a = 1;
+    return 1;
+  } else if ((digits = digits_base10_64(n)) % 2 == 0) {
+    split_base10(n, digits, a, b);
+    return 2;
+  } else {
+    *a = n * 2024;
+    return 1;
+  }
+}
+
+struct entry {
+  int64_t n;
+  int32_t depth;
+  int32_t _;
+  int64_t value;
+};
+
+#define CACHE_LENGTH (262144)
+
+struct cache {
+  struct entry entry[CACHE_LENGTH];
+  volatile int length;
+};
+
+static void sift_up(struct entry * e, int ix)
+{
+  while (ix > 0) {
+    int parent = (ix - 1) / 2;
+    if (e[parent].depth < e[ix].depth || e[parent].n < e[ix].n) {
+      // swap parent and ix
+      struct entry tmp = e[parent];
+      e[parent] = e[ix];
+      e[ix] = tmp;
+      ix = parent;
+    } else {
+      return;
+    }
+  }
+}
+
+static int search(struct entry * e, int length, int ix, int64_t n, int32_t depth)
+{
+  if (e[ix].depth == depth && e[ix].n == n) {
+    /*
+    uint32_t r15;
+    asm volatile ("mov r15,%0"
+                  : "=r" (r15));
+    if (r15 < min) {
+      //printf("%08x\n", r15);
+      min = r15;
+    }
+    */
+
+    return ix;
+  }
+
+  int child_l = 2 * ix + 1;
+  int child_r = 2 * ix + 2;
+
+  if (child_r < length && (e[child_r].depth >= depth || e[child_r].n >= n)) {
+    int i = search(e, length, child_r, n, depth);
+    if (i >= 0)
+      return i;
+  }
+
+  if (child_l < length && (e[child_l].depth >= depth || e[child_l].n >= n)) {
+    int i = search(e, length, child_l, n, depth);
+    if (i >= 0)
+      return i;
+  }
+
+  return -1;
+}
+
+static void cache_add(struct cache * cache, int64_t n, int32_t depth, int64_t value)
+{
+  if (cache->length >= CACHE_LENGTH)
+    return;
+
+  int ix = cache->length;
+  cache->entry[ix].n = n;
+  cache->entry[ix].depth = depth;
+  cache->entry[ix].value = value;
+  sift_up(cache->entry, ix);
+  cache->length += 1;
+}
+
+static int64_t simulate_step(int64_t n, int depth, int max_depth, struct cache * cache)
+{
+  if (depth == max_depth)
+    return 1;
+
+  int cache_ix = search(cache->entry, cache->length, 0, n, depth);
+  if (cache_ix >= 0) {
+    //printf("hit ix:%l %d %l\n", n, depth, cache->entry[cache_ix].value);
+    return cache->entry[cache_ix].value;
+  }
+
+  int64_t a[2];
+  int new_stones = stone_rule(n, &a[0], &a[1]);
+  int64_t sum = 0;
+  for (int i = 0; i < new_stones; i++) {
+    sum += simulate_step(a[i], depth + 1, max_depth, cache);
+  }
+
+  //printf("store: %l %d %l\n", n, depth, sum);
+  cache_add(cache, n, depth, sum);
+  return sum;
+}
+
+static int parse_input(const char * input, int length,
+                       int64_t * stones)
+{
+  const char * end = input + length;
+
+  int i = 0;
+  while (input < end) {
+    input = parse_base10_64(input, &stones[i]);
+    input = parse_skip(input, ' ');
+    input = parse_skip(input, '\n');
+    i += 1;
+  }
+  return i;
+}
+
+static int64_t solve(const char * input, int length, int max_depth)
+{
+  static struct cache cache;
+  int64_t stones[20];
+
+  int count = parse_input(input, length, stones);
+
+  int64_t sum = 0;
+  for (int i = 0; i < count; i++) {
+    cache.length = 0;
+    sum += simulate_step(stones[i], 0, max_depth, &cache);
+  }
+
+  return sum;
+}
+
+int64_t day11_part1(const char * input, int length)
+{
+  return solve(input, length, 25);
+}
+
+int64_t day11_part2(const char * input, int length)
+{
+  return solve(input, length, 75);
+}
diff --git a/input_dreamcast.inc b/input_dreamcast.inc
index 60d3f72..8cd0f57 100644
--- a/input_dreamcast.inc
+++ b/input_dreamcast.inc
@@ -19,6 +19,8 @@
 #include "day9/input.txt.h"
 #include "day10/sample1.txt.h"
 #include "day10/input.txt.h"
+#include "day11/sample1.txt.h"
+#include "day11/input.txt.h"
 
 static struct start_size sample[][2] = {
   {
@@ -81,6 +83,12 @@ static struct start_size sample[][2] = {
     { (  char *)&_binary_day10_sample1_txt_start,
       (uint32_t)&_binary_day10_sample1_txt_size   },
   },
+  {
+    { (  char *)&_binary_day11_sample1_txt_start,
+      (uint32_t)&_binary_day11_sample1_txt_size   },
+    { (  char *)&_binary_day11_sample1_txt_start,
+      (uint32_t)&_binary_day11_sample1_txt_size   },
+  },
 };
 
 static struct start_size input[] = {
@@ -104,4 +112,6 @@ static struct start_size input[] = {
     (uint32_t)&_binary_day9_input_txt_size   },
   { (  char *)&_binary_day10_input_txt_start,
     (uint32_t)&_binary_day10_input_txt_size   },
+  { (  char *)&_binary_day11_input_txt_start,
+    (uint32_t)&_binary_day11_input_txt_size   },
 };
diff --git a/runner.c b/runner.c
index 70529e5..986c790 100644
--- a/runner.c
+++ b/runner.c
@@ -32,7 +32,7 @@ bool runner_tick(struct runner_state * runner_state)
   int part = tick % 2;
   int day = tick / 2;
 
-  if (day < 9)
+  if (day < 10)
     return true;
 
   runner_state->want_render = solution[day].render != NULL;
diff --git a/runner.inc b/runner.inc
index 7af3b94..eafb2b2 100644
--- a/runner.inc
+++ b/runner.inc
@@ -21,6 +21,8 @@ int64_t day9_part1(const char * input, int length);
 int64_t day9_part2(const char * input, int length);
 int64_t day10_part1(const char * input, int length);
 int64_t day10_part2(const char * input, int length);
+int64_t day11_part1(const char * input, int length);
+int64_t day11_part2(const char * input, int length);
 
 struct day_funcs solution[] = {
   {
@@ -63,4 +65,8 @@ struct day_funcs solution[] = {
     {day10_part1, day10_part2},
     NULL,
   },
+  {
+    {day11_part1, day11_part2},
+    NULL,
+  },
 };
diff --git a/solutions.mk b/solutions.mk
index f388687..859b6a3 100644
--- a/solutions.mk
+++ b/solutions.mk
@@ -30,4 +30,7 @@ DAY_OBJ = \
 	day9/solution.o \
 	day10/sample1.txt.o \
 	day10/input.txt.o \
-	day10/solution.o
+	day10/solution.o \
+	day11/sample1.txt.o \
+	day11/input.txt.o \
+	day11/solution.o