unix: fix infinite recursion in itoa

Bring in http://golang.org/cl/138650044 from syscall package.

Change-Id: I554b0b31b981c682b6826644564971321a55c9e4
Reviewed-on: https://go-review.googlesource.com/10030Reviewed-by: Rob Pike <r@golang.org>

unix/export_test.go

+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package unix
+
+var Itoa = itoa

unix/str.go

@@ -8,8 +8,12 @@ package unix
 
 func itoa(val int) string { // do it here rather than with fmt to avoid dependency
 	if val < 0 {
-		return "-" + itoa(-val)
+		return "-" + uitoa(uint(-val))
 	}
+	return uitoa(uint(val))
+}
+
+func uitoa(val uint) string {
 	var buf [32]byte // big enough for int64
 	i := len(buf) - 1
 	for val >= 10 {

unix/syscall_test.go

@@ -7,6 +7,7 @@
 package unix_test
 
 import (
+	"fmt"
 	"testing"
 
 	"golang.org/x/sys/unix"
@@ -31,3 +32,19 @@ func TestEnv(t *testing.T) {
 	// make sure TESTENV gets set to "", not deleted
 	testSetGetenv(t, "TESTENV", "")
 }
+
+func TestItoa(t *testing.T) {
+	// Make most negative integer: 0x8000...
+	i := 1
+	for i<<1 != 0 {
+		i <<= 1
+	}
+	if i >= 0 {
+		t.Fatal("bad math")
+	}
+	s := unix.Itoa(i)
+	f := fmt.Sprint(i)
+	if s != f {
+		t.Fatalf("itoa(%d) = %s, want %s", i, s, f)
+	}
+}