go1.20 changed sorts up again

lib/sort/unsafe_go119.go

@@ -1,3 +1,6 @@
+//go:build !go1.20
+// +build !go1.20
+
 package sort
 
 import (

lib/sort/unsafe_go120.go

@@ -0,0 +1,25 @@
+package sort
+
+import (
+	"math/bits"
+	"sort"
+	_ "unsafe" // this is to explicitly signal this file is unsafe.
+)
+
+//go:linkname heapSort sort.heapSort
+func heapSort(data sort.Interface, a, b int)
+
+// quickSort is just an aliased call into pdqsort,
+// this means sort.go doesn’t need to be different between go1.19 and earlier.
+func quickSort(data sort.Interface, a, b, _ int) {
+	heapSort(data, a, b)
+}
+
+// maxDepth returns a threashold at which quicksort should switch to heapsort.
+// It returns 2 × ceil( log₂(n+1) )
+func maxDepth(n int) int {
+	if n <= 0 {
+		return 0
+	}
+	return 2 * bits.Len(uint(n))
+}