initial import of the C runtime

src/runtime/c/gu/choice.c

@@ -0,0 +1,73 @@
+#include <gu/choice.h>
+#include <gu/seq.h>
+#include <gu/assert.h>
+#include <gu/log.h>
+
+struct GuChoice {
+	GuBuf* path;
+	size_t path_idx;
+};
+
+GuChoice*
+gu_new_choice(GuPool* pool)
+{
+	GuChoice* ch = gu_new(GuChoice, pool);
+	ch->path = gu_new_buf(uint8_t, pool);
+	ch->path_idx = 0;
+	return ch;
+}
+
+GuChoiceMark
+gu_choice_mark(GuChoice* ch)
+{
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	gu_debug("%p@%d: mark", ch, ch->path_idx);
+	return (GuChoiceMark){ch->path_idx};
+}
+
+void
+gu_choice_reset(GuChoice* ch, GuChoiceMark mark)
+{
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	gu_debug("%p@%d: reset %d", ch, ch->path_idx, mark.path_idx);
+	gu_require(mark.path_idx <= ch->path_idx );
+	ch->path_idx = mark.path_idx;
+}
+
+int
+gu_choice_next(GuChoice* ch, int n_choices)
+{
+	gu_assert(n_choices >= 0);
+	gu_require(n_choices <= UINT8_MAX);
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	if (n_choices == 0) {
+		return -1;
+	}
+	int i = 0;
+	if (gu_buf_length(ch->path) > ch->path_idx) {
+		i = (int) gu_buf_get(ch->path, uint8_t, ch->path_idx);
+		gu_assert(i <= n_choices);
+	} else {
+		gu_buf_push(ch->path, uint8_t, n_choices);
+		i = n_choices;
+	}
+	int ret = (i == 0) ? -1 : n_choices - i;
+	gu_debug("%p@%d: %d", ch, ch->path_idx, ret);
+	ch->path_idx++;
+	return ret;
+}
+
+bool
+gu_choice_advance(GuChoice* ch)
+{
+	gu_assert(ch->path_idx <= gu_buf_length(ch->path));
+	
+	while (gu_buf_length(ch->path) > ch->path_idx) {
+		uint8_t last = gu_buf_pop(ch->path, uint8_t);
+		if (last > 1) {
+			gu_buf_push(ch->path, uint8_t, last-1);
+			return true;
+		}
+	}
+	return false;
+}