From 2a365287a88935578c765f5b3d5fa6111371d6de Mon Sep 17 00:00:00 2001
From: Patrick MARIE <pm@mkz.me>
Date: Sat, 24 Aug 2024 18:04:47 +0200
Subject: [PATCH] creating a VM (ch15)

---
 src/chunk.zig  | 100 +++++++++++++++++++++++++++++++++++++++++
 src/main.zig   | 118 ++++---------------------------------------------
 src/opcode.zig |   1 +
 src/utils.zig  |  20 +++++++++
 src/vm.zig     |  64 +++++++++++++++++++++++++++
 5 files changed, 193 insertions(+), 110 deletions(-)
 create mode 100644 src/chunk.zig
 create mode 100644 src/opcode.zig
 create mode 100644 src/vm.zig

diff --git a/src/chunk.zig b/src/chunk.zig
new file mode 100644
index 0000000..56c7130
--- /dev/null
+++ b/src/chunk.zig
@@ -0,0 +1,100 @@
+const std = @import("std");
+const debug = std.debug;
+const Allocator = std.mem.Allocator;
+
+const Value = @import("./values.zig").Value;
+const ValueArray = @import("./values.zig").ValueArray;
+const OpCode = @import("./opcode.zig").OpCode;
+
+const grow_capacity = @import("./utils.zig").grow_capacity;
+const utils = @import("./utils.zig");
+
+pub const Chunk = struct {
+    count: usize,
+    capacity: usize,
+    code: []u8,
+    lines: []usize,
+    constants: ValueArray,
+
+    pub fn new() Chunk {
+        return Chunk{
+            .count = 0,
+            .capacity = 0,
+            .code = &.{},
+            .lines = &.{},
+            .constants = ValueArray.new(),
+        };
+    }
+
+    pub fn init(self: *Chunk, allocator: Allocator) !void {
+        self.deinit(allocator);
+
+        self.count = 0;
+        self.capacity = 0;
+        self.code = &.{};
+        self.lines = &.{};
+        self.constants = ValueArray.new();
+    }
+
+    pub fn write(self: *Chunk, allocator: Allocator, byte: u8, line: usize) !void {
+        if (self.capacity < self.count + 1) {
+            const old_capacity = self.capacity;
+            self.capacity = grow_capacity(old_capacity);
+            self.code = try allocator.realloc(self.code, self.capacity);
+            self.lines = try allocator.realloc(self.lines, self.capacity);
+        }
+
+        self.code[self.count] = byte;
+        self.lines[self.count] = line;
+        self.count += 1;
+    }
+
+    pub fn dump(self: Chunk) void {
+        debug.print("{any}\n", .{self});
+    }
+
+    pub fn dissassemble(self: Chunk, name: []const u8) void {
+        debug.print("== {s} ==\n", .{name});
+
+        var offset: usize = 0;
+
+        while (offset < self.count) {
+            offset += self.dissassemble_instruction(offset);
+        }
+    }
+
+    pub fn dissassemble_instruction(self: Chunk, offset: usize) usize {
+        debug.print("{x:0>4} ", .{offset});
+
+        if (offset > 0 and self.lines[offset] == self.lines[offset - 1]) {
+            debug.print("   | ", .{});
+        } else {
+            debug.print("{d:4} ", .{self.lines[offset]});
+        }
+
+        const instruction = self.code[offset];
+
+        switch (instruction) {
+            @intFromEnum(OpCode.OP_RETURN) => return utils.simple_instruction("OP_RETURN", offset),
+            @intFromEnum(OpCode.OP_CONSTANT) => return utils.constant_instruction("OP_CONSTANT", self, offset),
+            else => {
+                debug.print("unknown opcode {d}\n", .{instruction});
+                return offset + 1;
+            },
+        }
+    }
+
+    pub fn deinit(self: *Chunk, allocator: Allocator) void {
+        self.constants.free(allocator);
+
+        if (self.capacity > 0) {
+            allocator.free(self.code);
+            allocator.free(self.lines);
+        }
+    }
+
+    pub fn add_constant(self: *Chunk, allocator: Allocator, value: Value) !usize {
+        try self.constants.write(allocator, value);
+        return self.constants.count - 1;
+    }
+};
diff --git a/src/main.zig b/src/main.zig
index 14645ec..0d3034a 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -2,122 +2,17 @@ const std = @import("std");
 const debug = std.debug;
 const Allocator = std.mem.Allocator;
 
-const utils = @import("./utils.zig");
-const values = @import("./values.zig");
-const Value = values.Value;
-const ValueArray = values.ValueArray;
-
-const OpCode = enum(u8) { OP_CONSTANT, OP_RETURN };
-
-const Chunk = struct {
-    count: usize,
-    capacity: usize,
-    code: []u8,
-    lines: []usize,
-    constants: ValueArray,
-
-    pub fn new() Chunk {
-        return Chunk{
-            .count = 0,
-            .capacity = 0,
-            .code = &.{},
-            .lines = &.{},
-            .constants = ValueArray.new(),
-        };
-    }
-
-    pub fn init(self: *Chunk, allocator: Allocator) !void {
-        self.deinit(allocator);
-
-        self.count = 0;
-        self.capacity = 0;
-        self.code = &.{};
-        self.lines = &.{};
-        self.constants = ValueArray.new();
-    }
-
-    pub fn write(self: *Chunk, allocator: Allocator, byte: u8, line: usize) !void {
-        if (self.capacity < self.count + 1) {
-            const old_capacity = self.capacity;
-            self.capacity = utils.grow_capacity(old_capacity);
-            self.code = try allocator.realloc(self.code, self.capacity);
-            self.lines = try allocator.realloc(self.lines, self.capacity);
-        }
-
-        self.code[self.count] = byte;
-        self.lines[self.count] = line;
-        self.count += 1;
-    }
-
-    pub fn dump(self: Chunk) void {
-        debug.print("{any}\n", .{self});
-    }
-
-    pub fn dissassemble(self: Chunk, name: []const u8) void {
-        debug.print("== {s} ==\n", .{name});
-
-        var offset: usize = 0;
-
-        while (offset < self.count) {
-            offset += self.dissassemble_instruction(offset);
-        }
-    }
-
-    pub fn dissassemble_instruction(self: Chunk, offset: usize) usize {
-        debug.print("{x:0>4} ", .{offset});
-
-        if (offset > 0 and self.lines[offset] == self.lines[offset - 1]) {
-            debug.print("   | ", .{});
-        } else {
-            debug.print("{d:4} ", .{self.lines[offset]});
-        }
-
-        const instruction = self.code[offset];
-
-        switch (instruction) {
-            @intFromEnum(OpCode.OP_RETURN) => return simple_instruction("OP_RETURN", offset),
-            @intFromEnum(OpCode.OP_CONSTANT) => return constant_instruction("OP_CONSTANT", self, offset),
-            else => {
-                debug.print("unknown opcode {d}\n", .{instruction});
-                return offset + 1;
-            },
-        }
-    }
-
-    pub fn deinit(self: *Chunk, allocator: Allocator) void {
-        self.constants.free(allocator);
-
-        if (self.capacity > 0) {
-            allocator.free(self.code);
-            allocator.free(self.lines);
-        }
-    }
-
-    pub fn add_constant(self: *Chunk, allocator: Allocator, value: Value) !usize {
-        try self.constants.write(allocator, value);
-        return self.constants.count - 1;
-    }
-};
-
-pub fn simple_instruction(opcode_name: []const u8, offset: usize) usize {
-    debug.print("{s:16}\n", .{opcode_name});
-
-    return offset + 1;
-}
-
-pub fn constant_instruction(opcode_name: []const u8, chunk: Chunk, offset: usize) usize {
-    const constant = chunk.code[offset + 1];
-    debug.print("{s:16} {d:4} '", .{ opcode_name, constant });
-    values.print_value(chunk.constants.values[constant]);
-    debug.print("'\n", .{});
-    return offset + 2;
-}
+const Chunk = @import("./chunk.zig").Chunk;
+const OpCode = @import("./opcode.zig").OpCode;
+const VM = @import("./vm.zig").VM;
 
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{ .safety = true }){};
     defer _ = debug.assert(gpa.deinit() == .ok);
     const allocator = gpa.allocator();
 
+    var vm = VM.new();
+
     var chunk = Chunk.new();
     try chunk.init(allocator);
 
@@ -128,5 +23,8 @@ pub fn main() !void {
 
     chunk.dissassemble("test chunk");
 
+    _ = vm.interpret(&chunk);
+    vm.free();
+
     chunk.deinit(allocator);
 }
diff --git a/src/opcode.zig b/src/opcode.zig
new file mode 100644
index 0000000..c99ab1b
--- /dev/null
+++ b/src/opcode.zig
@@ -0,0 +1 @@
+pub const OpCode = enum(u8) { OP_CONSTANT, OP_RETURN };
diff --git a/src/utils.zig b/src/utils.zig
index bd758bc..119cfc5 100644
--- a/src/utils.zig
+++ b/src/utils.zig
@@ -1,6 +1,26 @@
+const std = @import("std");
+const debug = std.debug;
+
+const Chunk = @import("./chunk.zig").Chunk;
+const print_value = @import("./values.zig").print_value;
+
 pub fn grow_capacity(capacity: usize) usize {
     if (capacity < 8) {
         return 8;
     }
     return capacity * 2;
 }
+
+pub fn simple_instruction(opcode_name: []const u8, offset: usize) usize {
+    debug.print("{s:16}\n", .{opcode_name});
+
+    return offset + 1;
+}
+
+pub fn constant_instruction(opcode_name: []const u8, chunk: Chunk, offset: usize) usize {
+    const constant = chunk.code[offset + 1];
+    debug.print("{s:16} {d:4} '", .{ opcode_name, constant });
+    print_value(chunk.constants.values[constant]);
+    debug.print("'\n", .{});
+    return offset + 2;
+}
diff --git a/src/vm.zig b/src/vm.zig
new file mode 100644
index 0000000..78ca569
--- /dev/null
+++ b/src/vm.zig
@@ -0,0 +1,64 @@
+const std = @import("std");
+const Chunk = @import("./chunk.zig").Chunk;
+const OpCode = @import("./opcode.zig").OpCode;
+const Value = @import("./values.zig").Value;
+
+const print_value = @import("./values.zig").print_value;
+
+const InterpretResult = enum {
+    OK,
+    COMPILE_ERROR,
+    RUNTIME_ERROR,
+};
+
+pub const VM = struct {
+    chunk: ?*Chunk,
+    ip: ?usize,
+
+    pub fn new() VM {
+        return VM{
+            .chunk = null,
+            .ip = null,
+        };
+    }
+
+    pub fn free(self: *VM) void {
+        _ = self;
+    }
+
+    pub fn interpret(self: *VM, chunk: *Chunk) InterpretResult {
+        self.chunk = chunk;
+        self.ip = 0;
+
+        return self.run();
+    }
+
+    pub fn run(self: *VM) InterpretResult {
+        while (true) {
+            const instruction = self.read_byte();
+
+            switch (instruction) {
+                @intFromEnum(OpCode.OP_CONSTANT) => {
+                    const constant = self.read_constant();
+                    print_value(constant);
+                },
+                @intFromEnum(OpCode.OP_RETURN) => return InterpretResult.OK,
+                else => return InterpretResult.RUNTIME_ERROR,
+            }
+        }
+
+        return InterpretResult.OK;
+    }
+
+    // XXX In the book, we're using a ptr to data directly, to avoid dereferencing to a given offset
+    // How to do that in Zig?
+    pub fn read_byte(self: *VM) u8 {
+        self.ip.? += 1;
+
+        return self.chunk.?.code[self.ip.?];
+    }
+
+    pub fn read_constant(self: *VM) Value {
+        return self.chunk.?.constants.values[read_byte(self)];
+    }
+};