Initial commit.

circ/lib.go

@@ -0,0 +1,59 @@
+package circ
+
+// B is a generic, non-concurrent circular FIFO buffer.
+type B[T any] struct {
+	buf  []T
+	len  int
+	head int
+	tail int
+}
+
+// Make creates a new circular buffer.
+func Make[T any](cap int) B[T] {
+	buf := make([]T, cap)
+	return B[T]{buf: buf}
+}
+
+// CanPush returns true if the buffer has space for new items.
+func (b *B[T]) CanPush() bool {
+	return cap(b.buf)-b.len != 0
+}
+
+// CanPop returns true if the buffer has one or more items.
+func (b *B[T]) CanPop() bool {
+	return b.len != 0
+}
+
+// PopFront returns the front-most item from the buffer.
+//
+// If the buffer is empty, it panics.
+func (b *B[T]) PopFront() T {
+	if !b.CanPop() {
+		panic("cannot pop from empty buffer")
+	}
+	var empty T
+	item := b.buf[b.head]
+	// clear buffer slot so that we don't hold on to garbage
+	b.buf[b.head] = empty
+	b.len--
+	b.head++
+	if b.head == cap(b.buf) {
+		b.head = 0
+	}
+	return item
+}
+
+// PushBack adds an item to the end of the buffer.
+//
+// If the buffer is full, it panics.
+func (b *B[T]) PushBack(value T) {
+	if !b.CanPush() {
+		panic("cannot push back to full buffer")
+	}
+	b.buf[b.tail] = value
+	b.len++
+	b.tail++
+	if b.tail == cap(b.buf) {
+		b.tail = 0
+	}
+}

circ/lib_test.go

@@ -0,0 +1,67 @@
+package circ_test
+
+import (
+	"testing"
+
+	"gogs.humancabbage.net/sam/priorityq/circ"
+)
+
+func TestRepeatPushPop(t *testing.T) {
+	t.Parallel()
+	cb := circ.Make[int](4)
+	for i := 0; i < 50; i++ {
+		cb.PushBack(1)
+		cb.PushBack(2)
+		cb.PushBack(3)
+		cb.PushBack(4)
+		checkPop := func(n int) {
+			if v := cb.PopFront(); v != n {
+				t.Errorf("popped %d, expected %d", v, n)
+			}
+		}
+		checkPop(1)
+		checkPop(2)
+		checkPop(3)
+		checkPop(4)
+	}
+}
+
+func TestInterleavedPushPop(t *testing.T) {
+	t.Parallel()
+	cb := circ.Make[int](4)
+	checkPop := func(n int) {
+		if v := cb.PopFront(); v != n {
+			t.Errorf("popped %d, expected %d", v, n)
+		}
+	}
+	cb.PushBack(1)
+	cb.PushBack(2)
+	cb.PushBack(3)
+	checkPop(1)
+	cb.PushBack(4)
+	cb.PushBack(5)
+	checkPop(2)
+}
+
+func TestEmptyPopPanic(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("popping empty buffer did not panic")
+		}
+	}()
+	t.Parallel()
+	cb := circ.Make[int](4)
+	cb.PopFront()
+}
+
+func TestFullPushPanic(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("pushing full buffer did not panic")
+		}
+	}()
+	t.Parallel()
+	cb := circ.Make[int](1)
+	cb.PushBack(1)
+	cb.PushBack(2)
+}