now

pub fn now() error{Unsupported}!Instant {
    const clock_id = switch (builtin.os.tag) {
        .windows => {
            // QPC on windows doesn't fail on >= XP/2000 and includes time suspended.
            return .{ .timestamp = windows.QueryPerformanceCounter() };
        },
        .wasi => {
            var ns: std.os.wasi.timestamp_t = undefined;
            const rc = std.os.wasi.clock_time_get(.MONOTONIC, 1, &ns);
            if (rc != .SUCCESS) return error.Unsupported;
            return .{ .timestamp = ns };
        },
        .uefi => {
            const value, _ = std.os.uefi.system_table.runtime_services.getTime() catch return error.Unsupported;
            return .{ .timestamp = value.toEpoch() };
        },
        // On darwin, use UPTIME_RAW instead of MONOTONIC as it ticks while
        // suspended.
        .macos, .ios, .tvos, .watchos, .visionos => posix.CLOCK.UPTIME_RAW,
        // On freebsd derivatives, use MONOTONIC_FAST as currently there's
        // no precision tradeoff.
        .freebsd, .dragonfly => posix.CLOCK.MONOTONIC_FAST,
        // On linux, use BOOTTIME instead of MONOTONIC as it ticks while
        // suspended.
        .linux => posix.CLOCK.BOOTTIME,
        // On other posix systems, MONOTONIC is generally the fastest and
        // ticks while suspended.
        else => posix.CLOCK.MONOTONIC,
    };

    const ts = posix.clock_gettime(clock_id) catch return error.Unsupported;
    return .{ .timestamp = ts };
}