<li>Give an error if unable to represent an integer constant
	    precisely.</li>

	<li>Give an error if unable to represent a floating-point or
	    complex constant due to overflow.</li>

	<li>Round to the nearest representable constant if unable to
	    represent a floating-point or complex constant due to limits
	    on precision.</li>
</ul>

<p>

import (
	"path"
	"runtime"
	"strings"
	"sync"
	"testing"
	"unsafe"
)

// Pass a func value from nestedCall to goCallback using an integer token.
var callbackMutex sync.Mutex
var callbackToken int
var callbackFuncs = make(map[int]func())

// nestedCall calls into C, back into Go, and finally to f.
func nestedCall(f func()) {
	// callback(x) calls goCallback(x)
	callbackMutex.Lock()
	callbackToken++
	i := callbackToken