You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: descriptor_unsafe.go
    path of file: ./repos/k6/vendor/github.com/jhump/protoreflect/desc
    
    the code of the file until where you have to start completion: //go:build !appengine && !gopherjs && !purego
// +build !appengine,!gopherjs,!purego

// NB: other environments where unsafe is unappropriate should use "purego" build tag
// https://github.com/golang/go/issues/23172

package desc

import (
	"sync/atomic"
	"unsafe"
)

type js
    
func (fd *FieldDescriptor) getDefaultValue() interface{} {
	addrOfDef := (*unsafe.Pointer)(unsafe.Pointer(&fd.def))
	def := atomic.LoadPointer(addrOfDef)
	if def != nil {
		return *(*interface{})(def)
	}
	// slow path: compute the default, potentially involves decoding value
	d := fd.determineDefault()
	atomic.StorePointer(addrOfDef, (unsafe.Pointer(&d)))
	return d
}