port rust tunnel example to zig

examples/zig/.gitignore

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+/zig-cache/
+/zig-out/

examples/zig/build.zig

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+const std = @import("std");
+
+pub fn build(b: *std.build.Builder) void {
+    const mode = std.builtin.Mode.ReleaseSmall;
+
+    const lib = b.addSharedLibrary("cart", "main.zig", .unversioned);
+    lib.setBuildMode(mode);
+    lib.setTarget(.{ .cpu_arch = .wasm32, .os_tag = .freestanding });
+    lib.import_memory = true;
+    lib.initial_memory = 262144;
+    lib.max_memory = 262144;
+    lib.global_base = 81920;
+    lib.stack_size = 8192;
+    lib.install();
+
+    if (lib.install_step) |install_step| {
+        const run_filter_exports = b.addSystemCommand(&[_][]const u8{
+            "uw8", "filter-exports", "zig-out/lib/cart.wasm", "zig-out/lib/cart-filtered.wasm"
+        });
+        run_filter_exports.step.dependOn(&install_step.step);
+
+        const run_wasm_opt = b.addSystemCommand(&[_][]const u8{
+            "wasm-opt", "-Oz", "-o", "zig-out/cart.wasm", "zig-out/lib/cart-filtered.wasm"
+        });
+        run_wasm_opt.step.dependOn(&run_filter_exports.step);
+
+        const run_uw8_pack = b.addSystemCommand(&[_][]const u8{
+            "uw8", "pack", "-l", "9", "zig-out/cart.wasm", "zig-out/cart.uw8"
+        });
+        run_uw8_pack.step.dependOn(&run_wasm_opt.step);
+
+        const make_opt = b.step("make_opt", "make size optimized cart");
+        make_opt.dependOn(&run_uw8_pack.step);
+
+        b.default_step = make_opt;
+    }
+}

examples/zig/main.zig

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+extern fn atan2(x: f32, y: f32) f32;
+extern fn time() f32;
+
+pub const FRAMEBUFFER: *[320*240]u8 = @intToPtr(*[320*240]u8, 120);
+
+export fn upd() void {
+    var i: u32 = 0;
+    while(true) {
+        var t = time() * 63.0;
+        var x = @intToFloat(f32, (@intCast(i32, i % 320) - 160));
+        var y = @intToFloat(f32, (@intCast(i32, i / 320) - 120));
+        var d = 40000.0 / @sqrt(x * x + y * y + 1.0);
+        var u = atan2(x, y) * 512.0 / 3.141;
+        var c = @intCast(u8, (@floatToInt(i32, d + t * 2.0) ^ @floatToInt(i32, u + t)) & 255) >> 4;
+
+        FRAMEBUFFER[@as(usize, i)] = c;
+        i += 1;
+        if(i >= 320*240) { break; }
+    }
+}