Handled distinctive NFDBits and func index's return values according to

different architectures.

Signed-off-by: xchenan <xchenan@gmail.com>

sys/select.go

@@ -1,8 +1,6 @@
 package sys
 
-import (
-	"syscall"
-)
+import "syscall"
 
 type FdSet syscall.FdSet
 

sys/select_32.go

@@ -0,0 +1,15 @@
+// +build darwin 386,freebsd arm,freebsd 386,linux arm,linux netbsd openbsd
+
+// Differnt architectures lead to different bits of uint
+// and different types of FdSet.Bits[].
+// Hence, NFDBits and types of func index's return values
+// have to be specified from case to case.
+
+package sys
+
+const NFDBits = 32
+
+func index(fd int) (idx uint, bit int32) {
+	u := uint(fd)
+	return u / NFDBits, 1 << (u % NFDBits)
+}

sys/select_64.go

@@ -0,0 +1,15 @@
+// +build amd64,dragonfly amd64,freebsd amd64,linux arm64,linux
+
+// Differnt architectures lead to different bits of uint
+// and different types of FdSet.Bits[].
+// Hence, NFDBits and types of func index's return values
+// have to be specified from case to case.
+
+package sys
+
+const NFDBits = 64
+
+func index(fd int) (idx uint, bit int64) {
+	u := uint(fd)
+	return u / NFDBits, 1 << (u % NFDBits)
+}

sys/select_bsd.go

@@ -4,13 +4,6 @@ package sys
 
 import "syscall"
 
-const NFDBits = 32
-
 func Select(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *syscall.Timeval) (err error) {
 	return syscall.Select(nfd, r.s(), w.s(), e.s(), timeout)
 }
-
-func index(fd int) (idx uint, bit int32) {
-	u := uint(fd)
-	return u / NFDBits, 1 << (u % NFDBits)
-}

sys/select_linux.go

@@ -4,14 +4,7 @@ package sys
 
 import "syscall"
 
-const NFDBits = 64
-
 func Select(nfd int, r *FdSet, w *FdSet, e *FdSet, timeout *syscall.Timeval) error {
 	_, err := syscall.Select(nfd, r.s(), w.s(), e.s(), timeout)
 	return err
 }
-
-func index(fd int) (idx uint, bit int64) {
-	u := uint(fd)
-	return u / NFDBits, 1 << (u % NFDBits)
-}