From 78f58a8fc7796a7684f898b857e0605711150592 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Thu, 9 Mar 2023 23:41:46 -0600
Subject: [PATCH] feat: initial commit

---
 .gitignore  |  2 ++
 build.zig   | 44 ++++++++++++++++++++++++++++++++++
 src/lib.zig | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 115 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 build.zig
 create mode 100644 src/lib.zig

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e73c965
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+zig-cache/
+zig-out/
diff --git a/build.zig b/build.zig
new file mode 100644
index 0000000..9345628
--- /dev/null
+++ b/build.zig
@@ -0,0 +1,44 @@
+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    const lib = b.addStaticLibrary(.{
+        .name = "zba-util",
+        // 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/lib.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This declares intent for the library to be installed into the standard
+    // location when the user invokes the "install" step (the default step when
+    // running `zig build`).
+    lib.install();
+
+    // Creates a step for unit testing.
+    const main_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build test`
+    // This will evaluate the `test` step rather than the default, which is "install".
+    const test_step = b.step("test", "Run library tests");
+    test_step.dependOn(&main_tests.step);
+}
diff --git a/src/lib.zig b/src/lib.zig
new file mode 100644
index 0000000..86dc023
--- /dev/null
+++ b/src/lib.zig
@@ -0,0 +1,69 @@
+const std = @import("std");
+
+pub fn RingBuffer(comptime T: type) type {
+    return struct {
+        const Self = @This();
+        const Index = usize;
+
+        const Atomic = std.atomic.Atomic;
+
+        const max_capacity = (@as(Index, 1) << @typeInfo(Index).Int.bits - 1) - 1; // half the range of index type
+        const log = std.log.scoped(.RingBuffer);
+
+        read: Atomic(Index),
+        write: Atomic(Index),
+        buf: []T,
+
+        const Error = error{buffer_full};
+
+        pub fn init(buf: []T) Self {
+            std.debug.assert(std.math.isPowerOfTwo(buf.len)); // capacity must be a power of two
+            std.debug.assert(buf.len <= max_capacity);
+
+            return .{
+                .read = Atomic(Index).init(0),
+                .write = Atomic(Index).init(0),
+                .buf = buf,
+            };
+        }
+
+        pub fn push(self: *Self, value: T) Error!void {
+            const read_idx = self.read.load(.Acquire);
+            const write_idx = self.write.load(.Acquire);
+
+            // Check to see if Queue is full
+            if (write_idx - read_idx == self.buf.len) return Error.buffer_full;
+
+            self.buf[self.mask(write_idx)] = value;
+
+            std.atomic.fence(.Release);
+            self.write.store(write_idx + 1, .Release);
+        }
+
+        pub fn pop(self: *Self) ?T {
+            const read_idx = self.read.load(.Acquire);
+            const write_idx = self.write.load(.Acquire);
+
+            if (read_idx == write_idx) return null;
+
+            std.atomic.fence(.Acquire);
+            const value = self.buf[self.mask(self.read)];
+
+            std.atomic.fence(.Release);
+            self.read.store(read_idx + 1, .Release);
+
+            return value;
+        }
+
+        pub fn len(self: *const Self) Index {
+            const read_idx = self.read.load(.Acquire);
+            const write_idx = self.write.load(.Acquire);
+
+            return write_idx - read_idx;
+        }
+
+        fn mask(self: *const Self, idx: Index) Index {
+            return idx & (self.buf.len - 1);
+        }
+    };
+}