From d60ba0002dc244a2b71e1c698ebeab1fac71b6a4 Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pjm@nac.net>
Date: Tue, 13 Dec 2011 01:33:24 -0500
Subject: Write tick() and friends.

Functions written:
  * void tick()
  * int count_live_neighbors(int i, int j)
  * bool get_cell(int i, int j)
  * void set_cell(int i, int j, bool s)
---
diff --git a/src/cgol.c b/src/cgol.c
index d4411d0..427df83 100644
--- a/src/cgol.c
+++ b/src/cgol.c
@@ -29,6 +29,10 @@ void init_curses();
 void init_game();
 void fini_game();
 void fini_curses();
+void tick();
+int count_live_neighbors(int i, int j);
+bool get_cell(int i, int j);
+void set_cell(int i, int j, bool s);
 void print_cell(int i, int j);
 void usage(const char *invocation);
 
@@ -162,6 +166,63 @@ fini_curses()
 }
 
 void
+tick()
+{
+	int i, j, n;
+	bool *grid_tmp;
+
+	for (i = 0; i < height; ++i) {
+		for (j = 0; j < width; ++j) {
+			n = count_live_neighbors(i, j);
+			if (get_cell(i, j)) {
+				if (n < 2 || n > 3) {
+					set_cell(i, j, false);
+					print_cell(i, j);
+				}
+			} else {
+				if (n == 3) {
+					set_cell(i, j, true);
+					print_cell(i, j);
+				}
+			}
+		}
+	}
+
+	/* Swap grids. */
+	grid_tmp = grid_cur;
+	grid_cur = grid_next;
+	grid_next = grid_tmp;
+}
+
+int
+count_live_neighbors(int i, int j)
+{
+	return
+		get_cell(i - 1, j - 1) + get_cell(i - 1, j) + get_cell(i - 1, j + 1) +
+		get_cell(i,     j - 1) +                      get_cell(i,     j + 1) +
+		get_cell(i + 1, j - 1) + get_cell(i + 1, j) + get_cell(i + 1, j + 1);
+}
+
+bool
+get_cell(int i, int j)
+{
+	if (i < 0 || j < 0 || i >= height || j >= width) {
+		/* This is something of a sanity check.  Anything off the finite grid
+		 * is by definition dead.  With this, count_live_neighbors() can be
+		 * dumb. */
+		return 0;
+	} else {
+		return grid_cur[i * width + j];
+	}
+}
+
+void
+set_cell(int i, int j, bool s)
+{
+	grid_cur[i * width + j] = s;
+}
+
+void
 print_cell(int i, int j)
 {
 	mvprintw(1 + i, 1 + j * 2, "%c", grid_cur[i * width + j] ? 'o' : ' ');
--
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