From 7b6aecf53fc5b71da941af3f874e81f53cd6bb47 Mon Sep 17 00:00:00 2001
From: "Haoran S. Diao" <0@hairydiode.xyz>
Date: Mon, 1 Apr 2019 19:37:32 -0400
Subject: functional conway's game of life with a glider

---
 .gitignore |   1 +
 Makefile   |   2 ++
 conway.c   | 103 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 106 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 conway.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..fe3d975
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+conway
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..b41e815
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,2 @@
+conway: conway.c
+	gcc conway.c -o conway
diff --git a/conway.c b/conway.c
new file mode 100644
index 0000000..db4dd0a
--- /dev/null
+++ b/conway.c
@@ -0,0 +1,103 @@
+#include <stdio.h>
+#define LOOP(col,line) \
+for (int j=0; j< 40; j++) { \
+	for (int i=0; i < 80; i++) { \
+		col \
+	} \
+	line \
+}
+
+/*
+ *Grid where everything is stored, 2nd least significant bit stores current
+ *state and least significant bit stores new state.
+ * The grid stores column position(x position) in the first field while row
+ * position( y position) is in the second field. As per c rules, this means that
+ * it is 80 wide by 40 tall, and the underlying datatype is a pointer to 80
+ * pointers stored in an array, each of which point to 40 chars stored in an
+ * array.
+ *
+ *We use char because it's close enough to uint8_t w/o having to include the
+ * standard into library.
+ */
+char grid[80][40] = {{0,0,2},{2,0,2},{0,2,2},0};
+
+/*
+ *determines whether a node should live(return 1) or die (return 0) based on
+ * it's current state
+ */
+int neighbor (int x, int y) {
+	/*neighbor count*/
+	int count = 0;
+	/*loops through all neighbors based off of y offset j and x offset i*/
+	for (int j = -1; j <= 1; j++) {
+		for (int i = -1; i <= 1; i++) {
+			/* makes sure to not count itself as a neighbor*/
+			if (!((i == 0) && (j == 0))) {
+				/*
+				 * modulo loops the grid back into itself
+				 * the addition of the value is required
+				 * otherwise strange nondeterministic behavior
+				 * occurs
+				 */
+				if ( grid[(x+i + 80 )%80][(y+j + 40)%40] & 0x02) {
+					count++;
+				}
+			}
+		}
+	}
+	/*
+	 * Switch determines the rules of conway's game of life
+	 */
+	switch (count) {
+		/*
+		 * The current population of a cell determines whether it lives
+		 * or die if it has 2 neighbors
+		 */
+		case 2: 
+			if (grid[x][y] & 0x02) {
+				return 1;
+			} else {
+				return 0;
+			}
+		case 3:
+			return 1;
+		default:
+			return 0;
+	}
+}
+int main (int argc, char * argv[]) {
+	/*
+	 * Stores the input character read from stdin. It's initialized to 0
+	 * because the main loop depends on it not being 'q'
+	 */
+	int r = 0;
+	/*
+	 * A do at least once loop that iterates through the game. It tests for
+	 * whether the character read from stdin is 'q'
+	 */
+	do {
+		/*
+		 * Input from stdin, this is blocking so it also serves as a delay
+		 */
+		r = fgetc(stdin);
+		/*
+		 * First it prints the current state stored in the 2nd least
+		 * significant bit. X if it is present, Y if it is not. This
+		 * loop is implemented as a macro b/c the entire loop has to be
+		 * run 3 different times. The first argument is to be run for
+		 * every cell while the 2nd one is to be run at the end of every
+		 * row
+		 */
+		LOOP(if (grid[i][j] & 0x02) {printf("X");}else{printf(",");},printf("\n"););
+		/*
+		 * Determines the current live/die state, then puts it into the
+		 * least significant bit representing the new state of the cell
+		 */
+		LOOP(grid[i][j] = neighbor(i,j) | (grid[i][j] & 0x02);,);
+		/*
+		 * Shifts the cell's state up, thereby making the new state the
+		 * current state and the new new state 0.
+		 */
+		LOOP(grid[i][j] = grid[i][j] << 1;,);
+	} while (r != 'q');
+}
-- 
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