// Copyright 2017 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.

// Functions to access/create device major and minor numbers matching the

// encoding used by the Linux kernel and glibc.

//

// The information below is extracted and adapted from bits/sysmacros.h in the

// glibc sources:

//

// dev_t in glibc is 64-bit, with 32-bit major and minor numbers. glibc's

// default encoding is MMMM Mmmm mmmM MMmm, where M is a hex digit of the major

// number and m is a hex digit of the minor number. This is backward compatible

// with legacy systems where dev_t is 16 bits wide, encoded as MMmm. It is also

// backward compatible with the Linux kernel, which for some architectures uses

// 32-bit dev_t, encoded as mmmM MMmm.

package unix

// Major returns the major component of a Linux device number.

func Major(dev uint64) uint32 {

	major := uint32((dev & 0x00000000000fff00) >> 8)

	major |= uint32((dev & 0xfffff00000000000) >> 32)

	return major

}

// Minor returns the minor component of a Linux device number.

func Minor(dev uint64) uint32 {

	minor := uint32((dev & 0x00000000000000ff) >> 0)

	minor |= uint32((dev & 0x00000ffffff00000) >> 12)

	return minor

}

// Mkdev returns a Linux device number generated from the given major and minor

// components.

func Mkdev(major, minor uint32) uint64 {

	dev := (uint64(major) & 0x00000fff) << 8

	dev |= (uint64(major) & 0xfffff000) << 32

	dev |= (uint64(minor) & 0x000000ff) << 0

	dev |= (uint64(minor) & 0xffffff00) << 12

	return dev

}