lib/sort: updates for go1.19

lib/sort/unsafe_go119.go

@@ -0,0 +1,25 @@
+package sort
+
+import (
+	"math/bits"
+	"sort"
+	_ "unsafe" // this is to explicitly signal this file is unsafe.
+)
+
+//go:linkname pdqsort sort.pdqsort
+func pdqsort(data sort.Interface, a, b, maxDepth 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, maxDepth int) {
+	pdqsort(data, a, b, maxDepth/2)
+}
+
+// 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))
+}

lib/sort/unsafe_pre119.go

@@ -1,3 +1,6 @@
+//go:build !go1.19
+// +build !go1.19
+
 package sort
 
 import (