From 52ac8d952fe7c722e33a3237e465dcf258076613 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Fri, 10 Mar 2023 00:00:48 -0600
Subject: [PATCH] chore: move Channel, Ringbuffer, rotr, sext impls to lib

---
 src/lib.zig | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 2 deletions(-)

diff --git a/src/lib.zig b/src/lib.zig
index 86dc023..4df9855 100644
--- a/src/lib.zig
+++ b/src/lib.zig
@@ -1,6 +1,8 @@
 const std = @import("std");
 
-pub fn RingBuffer(comptime T: type) type {
+const Log2Int = std.math.Log2Int;
+
+pub fn Channel(comptime T: type) type {
     return struct {
         const Self = @This();
         const Index = usize;
@@ -8,7 +10,7 @@ pub fn RingBuffer(comptime T: type) type {
         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);
+        const log = std.log.scoped(.Channel);
 
         read: Atomic(Index),
         write: Atomic(Index),
@@ -67,3 +69,94 @@ pub fn RingBuffer(comptime T: type) type {
         }
     };
 }
+
+pub fn RingBuffer(comptime T: type) type {
+    return struct {
+        const Self = @This();
+        const Index = usize;
+        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: Index,
+        write: 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);
+
+            std.mem.set(T, buf, 0);
+
+            return .{ .read = 0, .write = 0, .buf = buf };
+        }
+
+        pub fn push(self: *Self, value: T) Error!void {
+            if (self.isFull()) return error.buffer_full;
+            defer self.write += 1;
+
+            self.buf[self.mask(self.write)] = value;
+        }
+
+        pub fn pop(self: *Self) ?T {
+            if (self.isEmpty()) return null;
+            defer self.read += 1;
+
+            return self.buf[self.mask(self.read)];
+        }
+
+        /// Returns the number of entries read
+        pub fn copy(self: *const Self, cpy: []T) Index {
+            const count = std.math.min(self.len(), cpy.len);
+            var start: Index = self.read;
+
+            for (cpy, 0..) |*v, i| {
+                if (i >= count) break;
+
+                v.* = self.buf[self.mask(start)];
+                start += 1;
+            }
+
+            return count;
+        }
+
+        fn len(self: *const Self) Index {
+            return self.write - self.read;
+        }
+
+        fn isFull(self: *const Self) bool {
+            return self.len() == self.buf.len;
+        }
+
+        fn isEmpty(self: *const Self) bool {
+            return self.read == self.write;
+        }
+
+        fn mask(self: *const Self, idx: Index) Index {
+            return idx & (self.buf.len - 1);
+        }
+    };
+}
+
+// Sign-Extend value of type `T` to type `U`
+pub fn sext(comptime T: type, comptime U: type, value: T) T {
+    // U must have less bits than T
+    comptime std.debug.assert(@typeInfo(U).Int.bits <= @typeInfo(T).Int.bits);
+
+    const iT = std.meta.Int(.signed, @typeInfo(T).Int.bits);
+    const ExtU = if (@typeInfo(U).Int.signedness == .unsigned) T else iT;
+    const shift_amt = @intCast(Log2Int(T), @typeInfo(T).Int.bits - @typeInfo(U).Int.bits);
+
+    return @bitCast(T, @bitCast(iT, @as(ExtU, @truncate(U, value)) << shift_amt) >> shift_amt);
+}
+
+/// See https://godbolt.org/z/W3en9Eche
+pub inline fn rotr(comptime T: type, x: T, r: anytype) T {
+    if (@typeInfo(T).Int.signedness == .signed)
+        @compileError("cannot rotate signed integer");
+
+    const ar = @intCast(Log2Int(T), @mod(r, @typeInfo(T).Int.bits));
+    return x >> ar | x << (1 +% ~ar);
+}
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