Added an example program fib.c

This is simply a program with an embedded set of instructions which
indefinitely computes and prints fibonacci numbers, computing them in
pairs.

Does it completely through the virtual machine rather than just hard C
instructions.

Also amended the Makefile to compile it.  Required moving the main.c
object file into the dependencies of $(DIST)/$(OUT).

I should track the dependencies for fib.c and main.c as well.

2 files changed, 88 insertions, 4 deletions

diff --git a/Makefile b/Makefile
index 27c1fb4..1ba2079 100644
--- a/Makefile
+++ b/Makefile
@@ -13,9 +13,9 @@ OUT=ovm.out
 SRC=src
 DIST=build
 
-CODE=$(addprefix $(SRC)/, darr.c inst.c runtime.c main.c)
+CODE=$(addprefix $(SRC)/, darr.c inst.c runtime.c)
 OBJECTS=$(CODE:$(SRC)/%.c=$(DIST)/%.o)
-DEPS=$(OBJECTS:%.o=%.d)
+DEPS=$(OBJECTS:%.o=%.d) $(DIST)/fib.d $(DIST)/main.d
 
 .PHONY: all
 all: $(OUT) $(DIST)
@@ -25,14 +25,19 @@ $(DIST):
 
 $(OUT): $(DIST)/$(OUT)
 
-$(DIST)/$(OUT): $(DIST) $(OBJECTS)
-	$(CC) $(CFLAGS) $(OBJECTS) -o $@ $(LIBS)
+$(DIST)/$(OUT): $(DIST) $(OBJECTS) $(DIST)/main.o
+	$(CC) $(CFLAGS) $(OBJECTS) $(DIST)/main.o -o $@ $(LIBS)
 
 -include $(DEPS)
 
 $(DIST)/%.o: $(SRC)/%.c
 	$(CC) $(CFLAGS) -MMD -c $< -o $@ $(LIBS)
 
+examples: $(DIST)/fib.out
+
+$(DIST)/fib.out: $(DIST) $(OBJECTS) $(SRC)/fib.c
+	$(CC) $(CFLAGS) $(OBJECTS) $(SRC)/fib.c -o $@ $(LIBS)
+
 .PHONY: run
 run: $(DIST)/$(OUT)
 	./$^ $(ARGS)
diff --git a/src/fib.c b/src/fib.c
new file mode 100644
index 0000000..7107c3e
--- /dev/null
+++ b/src/fib.c
@@ -0,0 +1,79 @@
+/* Copyright (C) 2023 Aryadev Chavali
+
+ * You may distribute and modify this code under the terms of the GPLv2
+ * license.  You should have received a copy of the GPLv2 license with
+ * this file.  If not, please write to: aryadev@aryadevchavali.com.
+
+ * Created: 2023-10-23
+ * Author: Aryadev Chavali
+ * Description: An example virtual machine program which computes and
+ * prints fibonacci numbers.  Note that by default the virtual machine
+ * just rolls overflows over, so this program will never terminate.
+ */
+
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "./inst.h"
+#include "./runtime.h"
+
+int main(void)
+{
+  inst_t instructions[] = {
+      // MOV the values 1 and 1 to REG[0] and REG[1] respectively
+      INST_PUSH(WORD, 1),
+      INST_MOV(WORD, 0),
+      INST_PUSH(WORD, 1),
+      INST_MOV(WORD, 1),
+
+      // Print value at register 0 with newline.
+      INST_PUSH_REG(WORD, 0), // <-- #
+      INST_PRINT(WORD),
+      INST_PUSH(BYTE, '\n'),
+      INST_PRINT(CHAR),
+
+      // Print value at register 1 with newline
+      INST_PUSH_REG(WORD, 1),
+      INST_PRINT(WORD),
+      INST_PUSH(BYTE, '\n'),
+      INST_PRINT(CHAR),
+
+      /* Compute the next pair of fibonacci numbers */
+      // REG[0] + REG[1]
+      INST_PUSH_REG(WORD, 0),
+      INST_PUSH_REG(WORD, 1),
+      INST_PLUS(WORD),
+
+      // Mov REG[0] + REG[1] to REG[0]
+      INST_MOV(WORD, 0),
+
+      // REG[0] + REG[1]
+      INST_PUSH_REG(WORD, 0),
+      INST_PUSH_REG(WORD, 1),
+      INST_PLUS(WORD),
+
+      // Mov REG[0] + REG[1] to REG[1]
+      INST_MOV(WORD, 1),
+
+      // Jump to the point #
+      INST_JUMP_ABS(4),
+      INST_HALT,
+  };
+
+  byte stack[256];
+  vm_t vm = {0};
+  vm_load_stack(&vm, stack, ARR_SIZE(stack));
+  vm_load_program(&vm, instructions, ARR_SIZE(instructions));
+  err_t err = vm_execute_all(&vm);
+
+  if (err)
+  {
+    const char *error_str = err_as_cstr(err);
+    fprintf(stderr, "[ERROR]: %s\n", error_str);
+    fprintf(stderr, "[ERROR]: VM Trace:\n");
+    vm_print_all(&vm, stderr);
+    return 255 - err;
+  }
+  return 0;
+}