src/core: move mach-core@9a4d09707d9f1cb6ea5602bdf58caeefc46146be package to here

Helps hexops/mach#1165

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/core/Frequency.zig

@@ -0,0 +1,66 @@
+const std = @import("std");
+const core = @import("main.zig");
+const Timer = @import("Timer.zig");
+
+pub const Frequency = @This();
+
+/// The target frequency (e.g. 60hz) or zero for unlimited
+target: u32 = 0,
+
+/// The estimated delay that is needed to achieve the target frequency. Updated during tick()
+delay_ns: u64 = 0,
+
+/// The actual measured frequency. This is updated every second.
+rate: u32 = 0,
+
+delta_time: ?*f32 = null,
+delta_time_ns: *u64 = undefined,
+
+/// Internal fields, this must be initialized via a call to start().
+internal: struct {
+    // The frame number in this second's cycle. e.g. zero to 59
+    count: u32,
+    timer: Timer,
+    last_time: u64,
+} = undefined,
+
+/// Starts the timer used for frequency calculation. Must be called once before anything else.
+pub fn start(f: *Frequency) !void {
+    f.internal = .{
+        .count = 0,
+        .timer = try Timer.start(),
+        .last_time = 0,
+    };
+}
+
+/// Tick should be called at each occurrence (e.g. frame)
+pub inline fn tick(f: *Frequency) void {
+    var current_time = f.internal.timer.readPrecise();
+
+    if (f.delta_time) |delta_time| {
+        f.delta_time_ns.* = current_time -| f.internal.last_time;
+        delta_time.* = @as(f32, @floatFromInt(f.delta_time_ns.*)) / @as(f32, @floatFromInt(std.time.ns_per_s));
+    }
+
+    if (current_time >= std.time.ns_per_s) {
+        f.rate = f.internal.count;
+        f.internal.count = 0;
+        f.internal.timer.reset();
+        current_time -= std.time.ns_per_s;
+    }
+    f.internal.last_time = current_time;
+    f.internal.count += 1;
+
+    if (f.target != 0) {
+        const limited_count = @min(f.target, f.internal.count);
+        const target_time_per_tick: u64 = (std.time.ns_per_s / f.target);
+        const target_time = target_time_per_tick * limited_count;
+        if (current_time > target_time) {
+            f.delay_ns = 0;
+        } else {
+            f.delay_ns = target_time - current_time;
+        }
+    } else {
+        f.delay_ns = 0;
+    }
+}