From db35f7b87c26a7906eeca632b79f2569d2d14599 Mon Sep 17 00:00:00 2001
From: Ben Grant <benjamin.j.grant@gmail.com>
Date: Wed, 15 May 2024 17:58:46 -0700
Subject: [PATCH] Benchmark harness

---
 build.zig     | 31 ++++++++++++++++++++++++-------
 src/bench.zig | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 7 deletions(-)
 create mode 100644 src/bench.zig

diff --git a/build.zig b/build.zig
index 9fd3ecd..a0484c1 100644
--- a/build.zig
+++ b/build.zig
@@ -49,7 +49,7 @@ pub fn build(b: *std.Build) void {
 
     const native_library = b.addSharedLibrary(.{
         .name = "zip8",
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = target,
         .optimize = optimize,
     });
@@ -58,12 +58,31 @@ pub fn build(b: *std.Build) void {
         native_library.getEmittedBin(),
         b.fmt("libzip8{s}", .{target.result.dynamicLibSuffix()}),
     );
+    b.default_step.dependOn(&native_library_install.step);
+
+    const bench = b.addExecutable(.{
+        .name = "bench",
+        .root_source_file = b.path("src/bench.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    bench.root_module.addImport("build_options", options_module);
+    const bench_runner = b.addInstallBinFile(bench.getEmittedBin(), "bench");
+    const bench_install_step = b.step("bench", "Compile a benchmark harness");
+    bench_install_step.dependOn(&bench_runner.step);
+
+    const bench_run = b.addRunArtifact(bench);
+    if (b.args) |args| {
+        bench_run.addArgs(args);
+    }
+    const bench_run_step = b.step("run-bench", "Run the benchmark");
+    bench_run_step.dependOn(&bench_run.step);
 
     const wasm_library = b.addExecutable(.{
         .name = "zip8",
         // In this case the main source file is merely a path, however, in more
         // complicated build scripts, this could be a generated file.
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = b.resolveTargetQuery(.{
             .cpu_arch = .wasm32,
             .os_tag = .freestanding,
@@ -103,7 +122,7 @@ pub fn build(b: *std.Build) void {
         .name = "zip8",
         // In this case the main source file is merely a path, however, in more
         // complicated build scripts, this could be a generated file.
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = b.resolveTargetQuery(.{
             .cpu_arch = .thumb,
             .os_tag = .freestanding,
@@ -118,7 +137,7 @@ pub fn build(b: *std.Build) void {
     // build a static library for AVR
     const atmega4809_library = b.addStaticLibrary(.{
         .name = "zip8",
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = b.resolveTargetQuery(.{
             .cpu_arch = .avr,
             .os_tag = .freestanding,
@@ -192,11 +211,9 @@ pub fn build(b: *std.Build) void {
     const atmega4809_step = b.step("atmega4809", "Output a static library for ATmega4809");
     atmega4809_step.dependOn(&atmega4809_library_install.step);
 
-    b.default_step.dependOn(&native_library_install.step);
-
     // Creates a step for unit testing.
     const exe_tests = b.addTest(.{
-        .root_source_file = .{ .path = "src/main.zig" },
+        .root_source_file = b.path("src/main.zig"),
         .target = target,
         .optimize = optimize,
     });
diff --git a/src/bench.zig b/src/bench.zig
new file mode 100644
index 0000000..6e143f9
--- /dev/null
+++ b/src/bench.zig
@@ -0,0 +1,42 @@
+const std = @import("std");
+
+const Cpu = @import("./cpu.zig");
+
+pub const std_options = std.Options{
+    .log_level = .warn,
+};
+
+pub fn main() !void {
+    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
+    const allocator = arena.allocator();
+    const argv = try std.process.argsAlloc(allocator);
+    defer std.process.argsFree(allocator, argv);
+
+    if (argv.len != 3) {
+        std.log.err("usage: {s} <ROM path> <number of cycles>", .{argv[0]});
+        return error.BadUsage;
+    }
+
+    const rom = try std.fs.cwd().readFileAlloc(allocator, argv[1], Cpu.memory_size - Cpu.initial_pc);
+    defer allocator.free(rom);
+    const instructions = try std.fmt.parseInt(usize, argv[2], 10);
+
+    var cpu = try Cpu.init(rom, 0, .{0} ** 8);
+
+    const before = std.posix.getrusage(std.posix.rusage.SELF);
+    for (0..instructions) |_| {
+        try cpu.cycle();
+        cpu.dt = 0;
+    }
+    const after = std.posix.getrusage(std.posix.rusage.SELF);
+    const before_sec = @as(f64, @floatFromInt(before.utime.tv_sec)) +
+        @as(f64, @floatFromInt(before.utime.tv_usec)) / 1_000_000.0;
+    const after_sec = @as(f64, @floatFromInt(after.utime.tv_sec)) +
+        @as(f64, @floatFromInt(after.utime.tv_usec)) / 1_000_000.0;
+    const total_cpu_time = after_sec - before_sec;
+    const ins_per_sec = @as(f64, @floatFromInt(instructions)) / total_cpu_time;
+
+    var s: [64]u8 = undefined;
+    const written = try std.fmt.bufPrint(&s, "{}", .{std.fmt.fmtIntSizeDec(@intFromFloat(ins_per_sec))});
+    std.debug.print("{s} ins/sec\n", .{written[0 .. written.len - 1]});
+}