day18p2

day18p1/main.c

@@ -10,9 +10,10 @@ struct size2d {
 };
 
 struct buffer {
-    char *data;
+    void *data;
     size_t len;
     size_t alloc;
+    unsigned element;
 };
 
 void *xrealloc(void *ptr, size_t size)
@@ -25,22 +26,23 @@ void *xrealloc(void *ptr, size_t size)
     return res;
 }
 
-struct buffer buffer_alloc()
+struct buffer buffer_alloc(const unsigned element_size)
 {
     struct buffer buffer;
     buffer.len = 0;
     buffer.alloc = 0x10;
-    buffer.data = xrealloc(NULL, buffer.alloc);
+    buffer.element = element_size;
+    buffer.data = xrealloc(NULL, buffer.alloc * buffer.element);
     return buffer;
 }
 
-void buffer_append(struct buffer *buffer, char c)
+void buffer_append(struct buffer *buffer, void *data)
 {
     if (buffer->alloc <= buffer->len) {
         buffer->alloc *= 2;
-        buffer->data = xrealloc(buffer->data, buffer->alloc);
+        buffer->data = xrealloc(buffer->data, buffer->alloc * buffer->element);
     }
-    buffer->data[buffer->len++] = c;
+    memcpy((char *)buffer->data + buffer->len++ * buffer->element, data, buffer->element);
 }
 
 char *parse_acres(const char *fname, struct size2d *size)
@@ -51,7 +53,7 @@ char *parse_acres(const char *fname, struct size2d *size)
         return NULL;
     }
 
-    struct buffer buffer = buffer_alloc();
+    struct buffer buffer = buffer_alloc(sizeof(char));
     size->w = 0;
     size->h = 0;
 
@@ -79,7 +81,7 @@ char *parse_acres(const char *fname, struct size2d *size)
             goto error;
         }
 
-        buffer_append(&buffer, c);
+        buffer_append(&buffer, &c);
         width++;
     }
     funlockfile(f);
@@ -184,6 +186,19 @@ int render_bitmap(const char *fname, const char *acres, const struct size2d size
     return 0;
 }
 
+uint32_t adler32(const unsigned char *data, const size_t len)
+{
+    // Shamelessly copied from wikipedia...
+    uint32_t a = 1, b = 0;
+
+    for (size_t index = 0; index < len; index++) {
+        a = (a + data[index]) % 65521;
+        b = (b + a) % 65521;
+    }
+
+    return (b << 16) | a;
+}
+
 int main(int argc, char *argv[])
 {
     struct size2d size;
@@ -198,6 +213,10 @@ int main(int argc, char *argv[])
     char *next = xrealloc(NULL, size.w * size.h);
     memcpy(next, acres, size.w * size.h);
 
+    struct buffer hashes = buffer_alloc(sizeof(uint32_t));
+    unsigned loop_found = 0;
+    unsigned loop_iterlen = 0;
+
     char *fname = NULL;
     clock_t start = clock();
     for (unsigned i = 0; i <= minutes; i++) {
@@ -205,6 +224,24 @@ int main(int argc, char *argv[])
             advance_frame(acres, next, size);
             memcpy(acres, next, size.w * size.h);
 
+            if (!loop_found) {
+                uint32_t hash = adler32((unsigned char *)acres, size.w * size.h);
+                for (unsigned i = 0; i < hashes.len; i++) {
+                    uint32_t check = ((uint32_t *)hashes.data)[i];
+                    if (check == hash) {
+                        loop_found = i + 1;
+                        break;
+                    }
+                }
+
+                if (loop_found) {
+                    loop_iterlen = (i - loop_found);
+                    minutes = (minutes - i) % loop_iterlen + i;
+                } else {
+                    buffer_append(&hashes, &hash);
+                }
+            }
+
             if (i % 10000 == 0) {
                 double framespers = 10000 / ((double)(clock() - start) / CLOCKS_PER_SEC);
                 unsigned eta = (double)(minutes - i) / framespers;
@@ -235,8 +272,10 @@ int main(int argc, char *argv[])
         }
     }
 
+    if (loop_found) printf("Loop starting frame: %u (length %u)\n", loop_found, loop_iterlen);
     printf("Resource value: %u\n", wood * lumber);
 
+    free(hashes.data);
     free(next);
     free(acres);
     return 0;

day18p2

@@ -0,0 +1 @@
+day18p1