From 088674bf0b17cf494a4f57aba7685a73d14017df Mon Sep 17 00:00:00 2001
From: Luna <git@l4.pm>
Date: Sat, 1 Jun 2019 15:45:30 -0300
Subject: [PATCH] vm: add dynamically-sized growing stack

---
 src/main.zig |  2 +-
 src/vm.zig   | 60 ++++++++++++++++++++++++++++++----------------------
 2 files changed, 36 insertions(+), 26 deletions(-)

diff --git a/src/main.zig b/src/main.zig
index 8cd531f..b43afc1 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -123,6 +123,6 @@ pub fn main() !void {
     try chk.write(chunk.OpCode.Divide, 123);
     try chk.write(chunk.OpCode.Return, 123);
 
-    var vmach = vm.VM.init(stdout, &chk, true);
+    var vmach = try vm.VM.init(allocator, stdout, &chk, true);
     _ = try vmach.interpret();
 }
diff --git a/src/vm.zig b/src/vm.zig
index 990f81f..467651a 100644
--- a/src/vm.zig
+++ b/src/vm.zig
@@ -3,9 +3,9 @@ const chunk = @import("chunk.zig");
 const value = @import("value.zig");
 
 const Chunk = chunk.Chunk;
-const StdOut = *std.io.OutStream(std.fs.File.WriteError);
+const Value = value.Value;
 
-pub const STACK_MAX = 256;
+const StdOut = *std.io.OutStream(std.fs.File.WriteError);
 
 pub const InterpretResult = enum {
     Ok,
@@ -17,24 +17,30 @@ pub const VM = struct {
     chk: *Chunk,
     ip: usize = 0,
 
-    stack: [STACK_MAX]value.Value,
+    stack: []Value,
     stackTop: usize = 0,
 
     stdout: StdOut,
     debug_flag: bool,
+    allocator: *std.mem.Allocator,
 
     fn resetStack(self: *VM) void {
         self.stackTop = 0;
     }
 
-    pub fn init(stdout: StdOut, chk: *Chunk, debug_flag: bool) VM {
+    pub fn init(
+        allocator: *std.mem.Allocator,
+        stdout: StdOut,
+        chk: *Chunk,
+        debug_flag: bool,
+    ) !VM {
         var self = VM{
             .chk = chk,
 
-            // TODO move this to a nil value or something.
-            .stack = []value.Value{0} ** STACK_MAX,
+            .stack = try allocator.alloc(Value, 256),
             .stdout = stdout,
             .debug_flag = debug_flag,
+            .allocator = allocator,
         };
 
         self.resetStack();
@@ -54,11 +60,11 @@ pub const VM = struct {
         return byte;
     }
 
-    fn readConst(self: *VM) value.Value {
+    fn readConst(self: *VM) Value {
         return self.chk.constants.values[self.readByte()];
     }
 
-    fn readConstLong(self: *VM) value.Value {
+    fn readConstLong(self: *VM) Value {
         const v3 = self.readByte();
         const v2 = self.readByte();
         const v1 = self.readByte();
@@ -86,28 +92,28 @@ pub const VM = struct {
         return self.pop();
     }
 
-    fn doAdd(self: *VM) void {
+    fn doAdd(self: *VM) !void {
         var b = self.popNum();
         var a = self.popNum();
-        self.push(a + b);
+        try self.push(a + b);
     }
 
-    fn doSub(self: *VM) void {
+    fn doSub(self: *VM) !void {
         var b = self.popNum();
         var a = self.popNum();
-        self.push(a * b);
+        try self.push(a * b);
     }
 
-    fn doMul(self: *VM) void {
+    fn doMul(self: *VM) !void {
         var b = self.popNum();
         var a = self.popNum();
-        self.push(a * b);
+        try self.push(a * b);
     }
 
-    fn doDiv(self: *VM) void {
+    fn doDiv(self: *VM) !void {
         var b = self.popNum();
         var a = self.popNum();
-        self.push(a / b);
+        try self.push(a / b);
     }
 
     fn run(self: *VM) !InterpretResult {
@@ -122,12 +128,12 @@ pub const VM = struct {
             switch (instruction) {
                 chunk.OpCode.Constant => blk: {
                     var constant = self.readConst();
-                    self.push(constant);
+                    try self.push(constant);
                     break :blk;
                 },
                 chunk.OpCode.ConstantLong => blk: {
                     var constant = self.readConstLong();
-                    self.push(constant);
+                    try self.push(constant);
                     break :blk;
                 },
 
@@ -137,11 +143,11 @@ pub const VM = struct {
                     return InterpretResult.Ok;
                 },
 
-                chunk.OpCode.Add => self.doAdd(),
-                chunk.OpCode.Subtract => self.doSub(),
-                chunk.OpCode.Multiply => self.doMul(),
-                chunk.OpCode.Divide => self.doDiv(),
-                chunk.OpCode.Negate => self.push(-self.pop()),
+                chunk.OpCode.Add => try self.doAdd(),
+                chunk.OpCode.Subtract => try self.doSub(),
+                chunk.OpCode.Multiply => try self.doMul(),
+                chunk.OpCode.Divide => try self.doDiv(),
+                chunk.OpCode.Negate => try self.push(-self.pop()),
                 else => blk: {
                     std.debug.warn("Unknown instruction: {x}\n", instruction);
                     return InterpretResult.RuntimeError;
@@ -159,12 +165,16 @@ pub const VM = struct {
         return res;
     }
 
-    pub fn push(self: *VM, val: value.Value) void {
+    pub fn push(self: *VM, val: Value) !void {
+        if (self.stackTop > 0 and self.stackTop - 1 > self.stack.len) {
+            self.stack = try self.allocator.realloc(self.stack, self.stack.len + 1);
+        }
+
         self.stack[self.stackTop] = val;
         self.stackTop += 1;
     }
 
-    pub fn pop(self: *VM) value.Value {
+    pub fn pop(self: *VM) Value {
         self.stackTop -= 1;
         return self.stack[self.stackTop];
     }