- commit
- 2fd0f08
- parent
- 2fd0f08
- author
- Evgenii Akentev
- date
- 2025-11-01 20:17:50 +0400 +04
Little Computer 3 in Zig
5 files changed,
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2+# This file is for zig-specific build artifacts.
3+# If you have OS-specific or editor-specific files to ignore,
4+# such as *.swp or .DS_Store, put those in your global
5+# ~/.gitignore and put this in your ~/.gitconfig:
6+#
7+# [core]
8+# excludesfile = ~/.gitignore
9+#
10+# Cheers!
11+# -andrewrk
12+
13+.zig-cache/
14+zig-out/
15+/release/
16+/debug/
17+/build/
18+/build-*/
19+/docgen_tmp/
20+
21+# Although this was renamed to .zig-cache, let's leave it here for a few
22+# releases to make it less annoying to work with multiple branches.
23+zig-cache/
24+
+156,
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2+const std = @import("std");
3+
4+// Although this function looks imperative, it does not perform the build
5+// directly and instead it mutates the build graph (`b`) that will be then
6+// executed by an external runner. The functions in `std.Build` implement a DSL
7+// for defining build steps and express dependencies between them, allowing the
8+// build runner to parallelize the build automatically (and the cache system to
9+// know when a step doesn't need to be re-run).
10+pub fn build(b: *std.Build) void {
11+ // Standard target options allow the person running `zig build` to choose
12+ // what target to build for. Here we do not override the defaults, which
13+ // means any target is allowed, and the default is native. Other options
14+ // for restricting supported target set are available.
15+ const target = b.standardTargetOptions(.{});
16+ // Standard optimization options allow the person running `zig build` to select
17+ // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
18+ // set a preferred release mode, allowing the user to decide how to optimize.
19+ const optimize = b.standardOptimizeOption(.{});
20+ // It's also possible to define more custom flags to toggle optional features
21+ // of this build script using `b.option()`. All defined flags (including
22+ // target and optimize options) will be listed when running `zig build --help`
23+ // in this directory.
24+
25+ // This creates a module, which represents a collection of source files alongside
26+ // some compilation options, such as optimization mode and linked system libraries.
27+ // Zig modules are the preferred way of making Zig code available to consumers.
28+ // addModule defines a module that we intend to make available for importing
29+ // to our consumers. We must give it a name because a Zig package can expose
30+ // multiple modules and consumers will need to be able to specify which
31+ // module they want to access.
32+ const mod = b.addModule("lc3-vm_zig", .{
33+ // The root source file is the "entry point" of this module. Users of
34+ // this module will only be able to access public declarations contained
35+ // in this file, which means that if you have declarations that you
36+ // intend to expose to consumers that were defined in other files part
37+ // of this module, you will have to make sure to re-export them from
38+ // the root file.
39+ .root_source_file = b.path("src/root.zig"),
40+ // Later on we'll use this module as the root module of a test executable
41+ // which requires us to specify a target.
42+ .target = target,
43+ });
44+
45+ // Here we define an executable. An executable needs to have a root module
46+ // which needs to expose a `main` function. While we could add a main function
47+ // to the module defined above, it's sometimes preferable to split business
48+ // business logic and the CLI into two separate modules.
49+ //
50+ // If your goal is to create a Zig library for others to use, consider if
51+ // it might benefit from also exposing a CLI tool. A parser library for a
52+ // data serialization format could also bundle a CLI syntax checker, for example.
53+ //
54+ // If instead your goal is to create an executable, consider if users might
55+ // be interested in also being able to embed the core functionality of your
56+ // program in their own executable in order to avoid the overhead involved in
57+ // subprocessing your CLI tool.
58+ //
59+ // If neither case applies to you, feel free to delete the declaration you
60+ // don't need and to put everything under a single module.
61+ const exe = b.addExecutable(.{
62+ .name = "lc3-vm_zig",
63+ .root_module = b.createModule(.{
64+ // b.createModule defines a new module just like b.addModule but,
65+ // unlike b.addModule, it does not expose the module to consumers of
66+ // this package, which is why in this case we don't have to give it a name.
67+ .root_source_file = b.path("src/main.zig"),
68+ // Target and optimization levels must be explicitly wired in when
69+ // defining an executable or library (in the root module), and you
70+ // can also hardcode a specific target for an executable or library
71+ // definition if desireable (e.g. firmware for embedded devices).
72+ .target = target,
73+ .optimize = optimize,
74+ // List of modules available for import in source files part of the
75+ // root module.
76+ .imports = &.{
77+ // Here "lc3-vm_zig" is the name you will use in your source code to
78+ // import this module (e.g. `@import("lc3-vm_zig")`). The name is
79+ // repeated because you are allowed to rename your imports, which
80+ // can be extremely useful in case of collisions (which can happen
81+ // importing modules from different packages).
82+ .{ .name = "lc3-vm_zig", .module = mod },
83+ },
84+ }),
85+ });
86+
87+ // This declares intent for the executable to be installed into the
88+ // install prefix when running `zig build` (i.e. when executing the default
89+ // step). By default the install prefix is `zig-out/` but can be overridden
90+ // by passing `--prefix` or `-p`.
91+ b.installArtifact(exe);
92+
93+ // This creates a top level step. Top level steps have a name and can be
94+ // invoked by name when running `zig build` (e.g. `zig build run`).
95+ // This will evaluate the `run` step rather than the default step.
96+ // For a top level step to actually do something, it must depend on other
97+ // steps (e.g. a Run step, as we will see in a moment).
98+ const run_step = b.step("run", "Run the app");
99+
100+ // This creates a RunArtifact step in the build graph. A RunArtifact step
101+ // invokes an executable compiled by Zig. Steps will only be executed by the
102+ // runner if invoked directly by the user (in the case of top level steps)
103+ // or if another step depends on it, so it's up to you to define when and
104+ // how this Run step will be executed. In our case we want to run it when
105+ // the user runs `zig build run`, so we create a dependency link.
106+ const run_cmd = b.addRunArtifact(exe);
107+ run_step.dependOn(&run_cmd.step);
108+
109+ // By making the run step depend on the default step, it will be run from the
110+ // installation directory rather than directly from within the cache directory.
111+ run_cmd.step.dependOn(b.getInstallStep());
112+
113+ // This allows the user to pass arguments to the application in the build
114+ // command itself, like this: `zig build run -- arg1 arg2 etc`
115+ if (b.args) |args| {
116+ run_cmd.addArgs(args);
117+ }
118+
119+ // Creates an executable that will run `test` blocks from the provided module.
120+ // Here `mod` needs to define a target, which is why earlier we made sure to
121+ // set the releative field.
122+ const mod_tests = b.addTest(.{
123+ .root_module = mod,
124+ });
125+
126+ // A run step that will run the test executable.
127+ const run_mod_tests = b.addRunArtifact(mod_tests);
128+
129+ // Creates an executable that will run `test` blocks from the executable's
130+ // root module. Note that test executables only test one module at a time,
131+ // hence why we have to create two separate ones.
132+ const exe_tests = b.addTest(.{
133+ .root_module = exe.root_module,
134+ });
135+
136+ // A run step that will run the second test executable.
137+ const run_exe_tests = b.addRunArtifact(exe_tests);
138+
139+ // A top level step for running all tests. dependOn can be called multiple
140+ // times and since the two run steps do not depend on one another, this will
141+ // make the two of them run in parallel.
142+ const test_step = b.step("test", "Run tests");
143+ test_step.dependOn(&run_mod_tests.step);
144+ test_step.dependOn(&run_exe_tests.step);
145+
146+ // Just like flags, top level steps are also listed in the `--help` menu.
147+ //
148+ // The Zig build system is entirely implemented in userland, which means
149+ // that it cannot hook into private compiler APIs. All compilation work
150+ // orchestrated by the build system will result in other Zig compiler
151+ // subcommands being invoked with the right flags defined. You can observe
152+ // these invocations when one fails (or you pass a flag to increase
153+ // verbosity) to validate assumptions and diagnose problems.
154+ //
155+ // Lastly, the Zig build system is relatively simple and self-contained,
156+ // and reading its source code will allow you to master it.
157+}
+81,
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2+.{
3+ // This is the default name used by packages depending on this one. For
4+ // example, when a user runs `zig fetch --save <url>`, this field is used
5+ // as the key in the `dependencies` table. Although the user can choose a
6+ // different name, most users will stick with this provided value.
7+ //
8+ // It is redundant to include "zig" in this name because it is already
9+ // within the Zig package namespace.
10+ .name = .arithvm_zig,
11+ // This is a [Semantic Version](https://semver.org/).
12+ // In a future version of Zig it will be used for package deduplication.
13+ .version = "0.0.0",
14+ // Together with name, this represents a globally unique package
15+ // identifier. This field is generated by the Zig toolchain when the
16+ // package is first created, and then *never changes*. This allows
17+ // unambiguous detection of one package being an updated version of
18+ // another.
19+ //
20+ // When forking a Zig project, this id should be regenerated (delete the
21+ // field and run `zig build`) if the upstream project is still maintained.
22+ // Otherwise, the fork is *hostile*, attempting to take control over the
23+ // original project's identity. Thus it is recommended to leave the comment
24+ // on the following line intact, so that it shows up in code reviews that
25+ // modify the field.
26+ .fingerprint = 0x79da8ce1ed863de0, // Changing this has security and trust implications.
27+ // Tracks the earliest Zig version that the package considers to be a
28+ // supported use case.
29+ .minimum_zig_version = "0.15.1",
30+ // This field is optional.
31+ // Each dependency must either provide a `url` and `hash`, or a `path`.
32+ // `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
33+ // Once all dependencies are fetched, `zig build` no longer requires
34+ // internet connectivity.
35+ .dependencies = .{
36+ // See `zig fetch --save <url>` for a command-line interface for adding dependencies.
37+ //.example = .{
38+ // // When updating this field to a new URL, be sure to delete the corresponding
39+ // // `hash`, otherwise you are communicating that you expect to find the old hash at
40+ // // the new URL. If the contents of a URL change this will result in a hash mismatch
41+ // // which will prevent zig from using it.
42+ // .url = "https://example.com/foo.tar.gz",
43+ //
44+ // // This is computed from the file contents of the directory of files that is
45+ // // obtained after fetching `url` and applying the inclusion rules given by
46+ // // `paths`.
47+ // //
48+ // // This field is the source of truth; packages do not come from a `url`; they
49+ // // come from a `hash`. `url` is just one of many possible mirrors for how to
50+ // // obtain a package matching this `hash`.
51+ // //
52+ // // Uses the [multihash](https://multiformats.io/multihash/) format.
53+ // .hash = "...",
54+ //
55+ // // When this is provided, the package is found in a directory relative to the
56+ // // build root. In this case the package's hash is irrelevant and therefore not
57+ // // computed. This field and `url` are mutually exclusive.
58+ // .path = "foo",
59+ //
60+ // // When this is set to `true`, a package is declared to be lazily
61+ // // fetched. This makes the dependency only get fetched if it is
62+ // // actually used.
63+ // .lazy = false,
64+ //},
65+ },
66+ // Specifies the set of files and directories that are included in this package.
67+ // Only files and directories listed here are included in the `hash` that
68+ // is computed for this package. Only files listed here will remain on disk
69+ // when using the zig package manager. As a rule of thumb, one should list
70+ // files required for compilation plus any license(s).
71+ // Paths are relative to the build root. Use the empty string (`""`) to refer to
72+ // the build root itself.
73+ // A directory listed here means that all files within, recursively, are included.
74+ .paths = .{
75+ "build.zig",
76+ "build.zig.zon",
77+ "src",
78+ // For example...
79+ //"LICENSE",
80+ //"README.md",
81+ },
82+}
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2+const std = @import("std");
3+const lc3vm_zig = @import("lc3-vm_zig");
4+
5+pub fn main() !void {
6+ var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
7+ defer arena.deinit();
8+
9+ var memory = &lc3vm_zig.memory;
10+
11+ memory[0x3000] = 0xF026; // 1111 0000 0010 0110 TRAP trp_in_u16 ;read an uint16_t from stdin and put it in R0
12+ memory[0x3002] = 0x1220; // 0001 0010 0010 0000 ADD R1,R0,x0 ;add contents of R0 to R1
13+ memory[0x3003] = 0xF026; // 1111 0000 0010 0110 TRAP trp_in_u16 ;read an uint16_t from stdin and put it in R0
14+ memory[0x3004] = 0x1240; // 0001 0010 0010 0000 ADD R1,R1,R0 ;add contents of R0 to R1
15+ memory[0x3006] = 0x1060; // 0001 0000 0110 0000 ADD R0,R1,x0 ;add contents of R1 to R0
16+ memory[0x3007] = 0xF027; // 1111 0000 0010 0111 TRAP trp_out_u16;show the contents of R0 to stdout
17+ memory[0x3008] = 0xF025; // 1111 0000 0010 0101 HALT ;halt
18+
19+ try lc3vm_zig.start(arena.allocator(), 0);
20+}
21+
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2+//! By convention, root.zig is the root source file when making a library.
3+const std = @import("std");
4+
5+// Implementation of the Little Computer 3 following
6+// https://www.andreinc.net/2021/12/01/writing-a-simple-vm-in-less-than-125-lines-of-c
7+
8+const pcStart: u16 = 0x3000;
9+const u16Max: u32 = 65535;
10+pub var memory: [u16Max + 1]u16 = .{0} ** (u16Max + 1);
11+var running: bool = true;
12+
13+inline fn mr(address: u16) u16 { return memory[address]; }
14+
15+inline fn mw(address: u16, value: u16) void {
16+ memory[address] = value;
17+}
18+
19+const Register = enum(u16) {
20+ R0 = 0,
21+ R1 = 1,
22+ R2 = 2,
23+ R3 = 3,
24+ R4 = 4,
25+ R5 = 5,
26+ R6 = 6,
27+ R7 = 7,
28+ RPC = 8,
29+ RCND = 9,
30+ RCNT = 10
31+};
32+
33+var registers: [11]u16 = .{0} ** 11;
34+
35+// The instruction fits into u16:
36+//
37+// [ OP CODE ][ PARAM1 ][ PARAM2 ][ ][ PARAM3 ]
38+// [ 4 bits ][ 12 bits ]
39+
40+const Opcode = enum {
41+ br, // conditional
42+ add, // addition
43+ ld, // load RPC + offset
44+ st, // store
45+ jsr, // jump to subroutine
46+ andop, // bitwise and
47+ ldr, // load base + offset
48+ str, // store base + offset
49+ rti, // return from interrupt
50+ not, // bitwise complement
51+ ldi, // load indirect
52+ sti, // store indirect
53+ jmp, // jump/return to subroutine
54+ unused, // unused opcode
55+ lea, // load effective address
56+ trap, // system trap/call
57+
58+ pub fn parse(instruction: u16) Opcode {
59+ // shift 12 bits to the right to get first 4 bits
60+ return @enumFromInt(instruction >> 12);
61+ }
62+};
63+
64+const TrapFunc = enum {
65+ tgetc, tout, tputs, tin, tputsp, thalt, tinu16, toutu16,
66+
67+ pub fn parse(n: u16) TrapFunc {
68+ return @enumFromInt(n);
69+ }
70+};
71+
72+const Flag = enum(u16) {
73+ FP = (1 << 0),
74+ FZ = (1 << 1),
75+ FN = (1 << 2),
76+};
77+
78+inline fn uf(r: u16) void {
79+ if (registers[r] == 0) { registers[@intFromEnum(Register.RCND)] = @intFromEnum(Flag.FZ); }
80+ else if ((registers[r] >> 15) == 1) { registers[@intFromEnum(Register.RCND)] = @intFromEnum(Flag.FN); }
81+ else registers[@intFromEnum(Register.RCND)] = @intFromEnum(Flag.FP);
82+}
83+
84+inline fn fcnd(instruction: u16) u16 { return (instruction >> 9) & 0x7; }
85+inline fn dr(instruction: u16) u16 { return (instruction >> 9) & 0x7; }
86+inline fn sr1(instruction: u16) u16 { return(instruction >> 6) & 0x7; }
87+inline fn sr2(instruction: u16) u16 { return (instruction) & 0x7; }
88+inline fn imm(instruction: u16) u16 { return (instruction) & 0x1F; }
89+inline fn fimm(instruction: u16) u16 { return (instruction >> 5) & 1; }
90+
91+inline fn sext(n: u16, b: u32) u16 {
92+ return if ((n >> (b - 1)) & 1 == 1) @truncate(@as(u32, n) | (0xFFFF << b)) else n;
93+}
94+
95+// 0000 0000 0001 0110 <--- a in binary
96+// 1111 1111 1111 0110 <--- sextimm(a) in binary
97+inline fn sextimm(instruction: u16) u16 { return sext(imm(instruction), 5); }
98+
99+inline fn poff(instruction: u16) u16 { return sext(instruction & 0x3F, 6); }
100+inline fn poff9(instruction: u16) u16 { return sext(instruction & 0x1FF, 9); }
101+inline fn poff11(instruction: u16) u16 { return sext(instruction & 0x7FF, 11); }
102+inline fn fl(instruction: u16) u16 { return (instruction >> 11) & 1; }
103+inline fn br(instruction: u16) u16 { return (instruction >> 6) & 0x7; }
104+inline fn trp(instruction: u16) u16 { return instruction & 0xFF; }
105+
106+pub fn evaluate(allocator: std.mem.Allocator, i: u16) !void {
107+ switch (Opcode.parse(i)) {
108+ inline .add => {
109+ registers[dr(i)] = registers[sr1(i)] +
110+ if (fimm(i) == 1)
111+ sextimm(i)
112+ else registers[sr2(i)];
113+ uf(dr(i));
114+ },
115+ inline .andop => {
116+ registers[dr(i)] = registers[sr1(i)] & (if (fimm(i) == 1) (sextimm(i)) else registers[sr2(i)]);
117+ uf(dr(i));
118+ },
119+ inline .ld => {
120+ registers[dr(i)] = mr(registers[@intFromEnum(Register.RPC)] + poff9(i));
121+ uf(dr(i));
122+ },
123+ inline .ldi => {
124+ registers[dr(i)] = mr(mr(registers[@intFromEnum(Register.RPC)] + poff9(i)));
125+ uf(dr(i));
126+ },
127+ inline .ldr => {
128+ registers[dr(i)] = mr(registers[sr1(i)] + poff(i));
129+ uf(dr(i));
130+ },
131+ inline .lea => {
132+ registers[dr(i)] = registers[@intFromEnum(Register.RPC)] + poff9(i);
133+ uf(dr(i));
134+ },
135+ inline .not => {
136+ registers[dr(i)] = ~ registers[sr1(i)];
137+ uf(dr(i));
138+ },
139+ inline .st => {
140+ mw(registers[@intFromEnum(Register.RPC)] + poff9(i), registers[dr(i)]);
141+ },
142+ inline .sti => {
143+ mw(mr(registers[@intFromEnum(Register.RPC)] + poff9(i)), registers[dr(i)]);
144+ },
145+ inline .str => {
146+ mw(registers[sr1(i)] + poff(i), registers[dr(i)]);
147+ },
148+ inline .jmp => {
149+ registers[@intFromEnum(Register.RPC)] = registers[br(i)];
150+ },
151+ inline .jsr => {
152+ registers[@intFromEnum(Register.R7)] = registers[@intFromEnum(Register.RPC)];
153+ registers[@intFromEnum(Register.RPC)] = if (fl(i) == 1) (registers[@intFromEnum(Register.RPC)] + poff11(i)) else registers[br(i)];
154+ },
155+ inline .br => {
156+ if (registers[@intFromEnum(Register.RCND)] & fcnd(i) == 1) {
157+ registers[@intFromEnum(Register.RPC)] += poff9(i);
158+ }
159+ },
160+ inline .unused, .rti => {
161+ },
162+ inline .trap => {
163+ switch (TrapFunc.parse(trp(i) - 0x20)) {
164+ inline .tgetc => {
165+ const dest: []u8 = try allocator.alloc(u8, 1);
166+ _ = try std.fs.File.stdin().read(dest);
167+ registers[@intFromEnum(Register.R0)] = dest[0];
168+ },
169+ inline .tout => {
170+ std.debug.print("{}", .{ registers[@intFromEnum(Register.R0)] });
171+ },
172+ inline .tputs => {
173+ },
174+ inline .tin => {
175+ const buffer: []u8 = try allocator.alloc(u8, 1024);
176+ defer allocator.free(buffer);
177+
178+ var stdin = std.fs.File.stdin().reader(buffer).interface;
179+ const m = try stdin.takeInt(u8, .little);
180+ registers[@intFromEnum(Register.R0)] = m;
181+ },
182+ inline .thalt => {
183+ running = false;
184+ },
185+ inline .tinu16 => {
186+ const buffer: []u8 = try allocator.alloc(u8, 1024);
187+ defer allocator.free(buffer);
188+
189+ var line_buffer: []u8 = try allocator.alloc(u8, 1024);
190+ defer allocator.free(line_buffer);
191+ var writer: std.io.Writer = .fixed(line_buffer);
192+
193+ var stdin = std.fs.File.stdin().reader(buffer).interface;
194+
195+ const line_length = try stdin.streamDelimiterLimit(&writer, '\n', .unlimited);
196+ const v: u16 = try std.fmt.parseInt(u16, line_buffer[0..line_length], 10);
197+ registers[@intFromEnum(Register.R0)] = v;
198+ },
199+ inline .tputsp => {
200+ },
201+ inline .toutu16 => {
202+ const buffer: []u8 = try allocator.alloc(u8, 1024);
203+ defer allocator.free(buffer);
204+
205+ const v: u16 = registers[@intFromEnum(Register.R0)];
206+ std.debug.print("{}\n", .{ v });
207+ },
208+ }
209+ }
210+ }
211+}
212+
213+pub fn start(allocator: std.mem.Allocator, offset: u16) !void {
214+ registers[@intFromEnum(Register.RPC)] = pcStart + offset;
215+ while (running) {
216+ const instruction = mr(registers[@intFromEnum(Register.RPC)]);
217+ registers[@intFromEnum(Register.RPC)] += 1;
218+
219+ try evaluate(allocator, instruction);
220+ }
221+}
222+