+/* Return a uniformly-distributed pseudo-random integer within the
+ * range:
+ *
+ * 0 <= result < num_values
+ */
+static int
+rand_within (int num_values)
+{
+ return (int) (num_values * (rand() / (RAND_MAX + 1.0)));
+}
+
+/* Return an exponentially-distributed pseudo-random integer within
+ * the range:
+ *
+ * 0 <= result < num_values
+ *
+ * The distribution is such that each successively larger value will
+ * occur with a probability of half of the previous value.
+ */
+static int
+rand_within_exponential (int num_values)
+{
+ static int r;
+ static uint32_t mask = 0;
+ int ones;
+ int bit;
+
+ /* Optimize the constant case. */
+ if (num_values == 1)
+ return 0;
+
+ ones = 0;
+
+ do {
+ if (mask == 0) {
+ r = rand ();
+ mask = 1 << 31;
+ while (mask > RAND_MAX)
+ mask >>= 1;
+ }
+ bit = r & mask;
+ mask >>= 1;
+ if (bit) {
+ ones++;
+ if (ones == num_values)
+ ones = 0;
+ }
+ } while (bit);
+
+ return ones;
+}
+
+/* Find the category to which an item belongs. */
+static category_t *
+mnemon_item_category (mnemon_t *mnemon,
+ item_t *item)
+{
+ category_t *category;
+ int i, item_index;
+
+ for (i = 0; i < mnemon->num_categories; i++) {
+ category = &mnemon->categories[i];
+ item_index = item - category->items;
+ if (item_index >= 0 && item_index < category->num_items)
+ return category;
+ }
+
+ assert (0);
+}
+
+/* Return the number of items in the bin from the given category (or
+ * from all categories if category == NULL) */
+static int
+mnemon_bin_num_items_in_category (mnemon_t *mnemon,
+ bin_t *bin,
+ category_t *category)
+{
+ int i, num_items = 0;
+
+ if (category == NULL)
+ return bin->num_items;
+
+ for (i = 0; i < bin->num_items; i++)
+ if (mnemon_item_category (mnemon, bin->items[i]) == category)
+ num_items++;
+
+ return num_items;
+}
+
+static void
+mnemon_select_item (mnemon_t *mnemon,
+ bin_t **bin_ret,
+ int *item_index_ret)
+{
+ int bin_index, item_index;
+ bin_t *bin;
+
+ bin_index = rand_within_exponential (mnemon->num_bins);
+
+ bin = &mnemon->bins[bin_index];
+
+ item_index = rand_within (bin->num_items);
+
+ if (bin->score == 0) {
+ category_t *category;
+ item_t *item;
+
+ item = bin->items[item_index];
+
+ category = mnemon_item_category (mnemon, item);
+
+ if (category->order == CATEGORY_ORDER_SEQUENTIAL) {
+ item = category_next_bin_zero_item (category);
+ if (item)
+ item_index = bin_item_index (bin, item);
+ }
+ }
+
+ *bin_ret = bin;
+ *item_index_ret = item_index;
+}
+
+
+#define HISTOGRAM_ROW_FORMAT "%3d: %3d"
+#define HISTOGRAM_BAR_WIDTH 63
+
+static void
+print_histogram_bar (double size,
+ double max)
+{
+ int units_per_cell = (int) ceil (max / HISTOGRAM_BAR_WIDTH);
+ static char const *boxes[8] = {
+ "█", "▉", "▊", "▋",
+ "▌", "▍", "▎", "▏"
+ };
+
+ while (size > units_per_cell) {
+ printf(boxes[0]);
+ size -= units_per_cell;
+ }
+
+ size /= units_per_cell;
+
+ if (size > 7.5/8.0)
+ printf(boxes[0]);
+ else if (size > 6.5/8.0)
+ printf(boxes[1]);
+ else if (size > 5.5/8.0)
+ printf(boxes[2]);
+ else if (size > 4.5/8.0)
+ printf(boxes[3]);
+ else if (size > 3.5/8.0)
+ printf(boxes[4]);
+ else if (size > 2.5/8.0)
+ printf(boxes[5]);
+ else if (size > 1.5/8.0)
+ printf(boxes[6]);
+ else if (size > 0.5/8.0)
+ printf(boxes[7]);
+
+ printf ("\n");
+}
+
+static void
+mnemon_print_histogram (mnemon_t *mnemon,
+ const char *category_name)
+{
+ int i, last_score, max;
+ category_t *category = NULL;
+ bin_t *bin;
+ int num_items;
+
+ if (mnemon->num_bins == 0)
+ return;
+
+ if (category_name)
+ category = mnemon_get_category_if_exists (mnemon, category_name);
+
+ for (i = 0; i < mnemon->num_bins; i++) {
+ num_items = mnemon_bin_num_items_in_category (mnemon,
+ &mnemon->bins[i],
+ category);
+ if (i == 0 || num_items > max)
+ max = num_items;
+ }
+
+ for (i = 0; i < mnemon->num_bins; i++) {
+ bin = &mnemon->bins[i];
+ if (i != 0)
+ while (bin->score - last_score > 1)
+ printf (HISTOGRAM_ROW_FORMAT "\n", ++last_score, 0);
+ num_items = mnemon_bin_num_items_in_category (mnemon,
+ bin, category);
+ printf (HISTOGRAM_ROW_FORMAT " ", bin->score, num_items);
+ print_histogram_bar (num_items, max);
+ last_score = bin->score;
+ }
+}
+
+static void
+mnemon_handle_command (mnemon_t *mnemon,
+ const char *command)
+{
+ const char *arg;
+ switch (command[0]) {
+ case 'h':
+ arg = command + 1;
+ while (*arg && isspace (*arg))
+ arg++;
+ if (*arg == '\0')
+ arg = NULL;
+ mnemon_print_histogram (mnemon, arg);
+ break;
+ default:
+ printf ("Unknown command: %s\n", command);
+ break;
+ }
+}
+
+static void
+mnemon_handle_response (mnemon_t *mnemon,
+ bin_t *bin,
+ int item_index,
+ item_t *item,
+ const char *response)
+{
+ bool_t correct;
+
+ correct = (strcmp (response, item->response) == 0);
+
+ bin_remove_item (bin, item_index);
+
+ /* If the bin is now empty, we must remove it. Also if we just
+ * picked the last word we'll ever pick from the bin with
+ * score 0, then we can remove that as well. */
+ if (bin->num_items == 0 ||
+ (bin->score == 0 && mnemon->to_introduce == 0))
+ {
+ mnemon_remove_bin (mnemon, bin);
+ }
+
+ if (correct) {
+ item->score++;
+ /* We reserve an item score of 0 for an item that has
+ * never been asked. */
+ if (item->score == 0) {
+ item->score = 1;
+ mnemon->unlearned--;
+ printf ("You got it!");
+ } else if (item->score < 0) {
+ printf ("Yes---just give me %d more.",
+ - item->score);
+ } else if (item->score == 1) {
+ printf ("On your first try, no less!");
+ } else {
+ printf ("Masterful (%dx).", item->score);
+ if (mnemon->to_master)
+ mnemon->mastered++;
+ }
+ } else {
+ printf (" %s is the correct answer.",
+ item->response);
+ /* Penalize an incorrect response by forcing the score
+ * negative. */
+ if (item->score >= 0) {
+ if (item->score > 0)
+ printf ( " Oops, you knew that, right?\n ");
+ mnemon->unlearned++;
+ /* We go to -2 to force a little extra reinforcement
+ * when re-learning an item, (otherwise, it will often
+ * get asked again immediately where it is easy to get
+ * a correct response without any learning). */
+ item->score = -2;
+ } else {
+ item->score--;
+ }
+ }
+
+ if (mnemon->to_introduce == 0 &&
+ mnemon->unlearned == 0 &&
+ mnemon->to_master == 0)
+ {
+ mnemon->to_master = 10;
+ mnemon->mastered = 0;
+ }
+
+ printf (" ");
+ if (mnemon->to_introduce)
+ printf ("%d to come. ", mnemon->to_introduce);
+ if (mnemon->unlearned)
+ printf ("%d still unlearned. ", mnemon->unlearned);
+ if (mnemon->to_master) {
+ if (mnemon->mastered < mnemon->to_master)
+ printf ("%d items to master",
+ mnemon->to_master - mnemon->mastered);
+ else
+ printf ("Great job!");
+ }
+ printf ("\n\n");
+
+ bin = mnemon_get_bin (mnemon, item->score);
+
+ bin_add_item (bin, item);
+}
+
+static void
+mnemon_do_challenges (mnemon_t *mnemon)
+{
+ bin_t *bin;
+ int item_index;
+ item_t *item;
+ char *response;
+ int i;
+
+ /* Count the number of items with negative scores. */
+ mnemon->unlearned = 0;
+ for (i = 0; i < mnemon->num_bins; i++) {
+ bin = &mnemon->bins[i];
+ if (bin->score >= 0)
+ break;
+ mnemon->unlearned += bin->num_items;
+ }
+
+ mnemon->to_introduce -= mnemon->unlearned;
+ if (mnemon->to_introduce < 0)
+ mnemon->to_introduce = 0;
+
+ /* Get rid of bin with score of 0 if we aren't going to be
+ * introducing anything from it. */
+ if (mnemon->to_introduce == 0) {
+ bin = mnemon_get_bin (mnemon, 0);
+ mnemon_remove_bin (mnemon, bin);
+ }
+
+ if (mnemon->unlearned) {
+ printf ("You've got %d items to learn already. ", mnemon->unlearned);
+ if (mnemon->to_introduce)
+ printf ("I'll introduce %d more as we go.", mnemon->to_introduce);
+ printf ("\n");
+ } else {
+ printf ("Introducing %d new items.\n", mnemon->to_introduce);
+ }
+ printf ("\n");
+
+ do {
+ mnemon_select_item (mnemon, &bin, &item_index);
+ item = bin->items[item_index];
+
+ if (bin->score == 0)
+ mnemon->to_introduce--;
+
+ while (1) {
+ printf ("%s\n", item->challenge);
+
+ response = readline ("> ");
+ /* Terminate on EOF */
+ if (response == NULL) {
+ printf ("\n");
+ return;
+ }
+
+ if (response[0] == '/')
+ mnemon_handle_command (mnemon, response + 1);
+ else
+ break;
+ }
+
+ mnemon_handle_response (mnemon, bin, item_index,
+ item, response);
+ } while (mnemon->mastered < mnemon->to_master);
+}
+