// Copyright 2009 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

import "unsafe"

// readInt returns the size-bytes unsigned integer in native byte order at offset off.

func readInt(b []byte, off, size uintptr) (u uint64, ok bool) {

	if len(b) < int(off+size) {

		return 0, false

	}

	if isBigEndian {

		return readIntBE(b[off:], size), true

	}

	return readIntLE(b[off:], size), true

}

func readIntBE(b []byte, size uintptr) uint64 {

	switch size {

	case 1:

		return uint64(b[0])

	case 2:

		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808

		return uint64(b[1]) | uint64(b[0])<<8

	case 4:

		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808

		return uint64(b[3]) | uint64(b[2])<<8 | uint64(b[1])<<16 | uint64(b[0])<<24

	case 8:

		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808

		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |

			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56

	default:

		panic("syscall: readInt with unsupported size")

	}

}

func readIntLE(b []byte, size uintptr) uint64 {

	switch size {

	case 1:

		return uint64(b[0])

	case 2:

		_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808

		return uint64(b[0]) | uint64(b[1])<<8

	case 4:

		_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808

		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24

	case 8:

		_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808

		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |

			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56

	default:

		panic("syscall: readInt with unsupported size")

	}

}

// ParseDirent parses up to max directory entries in buf,

// appending the names to names. It returns the number of

// bytes consumed from buf, the number of entries added

// to names, and the new names slice.

func ParseDirent(buf []byte, max int, names []string) (consumed int, count int, newnames []string) {

	origlen := len(buf)

	count = 0

	for max != 0 && len(buf) > 0 {

		reclen, ok := direntReclen(buf)

		if !ok || reclen > uint64(len(buf)) {

			return origlen, count, names

		}

		rec := buf[:reclen]

		buf = buf[reclen:]

		ino, ok := direntIno(rec)

		if !ok {

			break

		}

		if ino == 0 { // File absent in directory.

			continue

		}

		const namoff = uint64(unsafe.Offsetof(Dirent{}.Name))

		namlen, ok := direntNamlen(rec)

		if !ok || namoff+namlen > uint64(len(rec)) {

			break

		}

		name := rec[namoff : namoff+namlen]

		for i, c := range name {

			if c == 0 {

				name = name[:i]

				break

			}

		}

		// Check for useless names before allocating a string.

		if string(name) == "." || string(name) == ".." {

			continue

		}

		max--

		count++

		names = append(names, string(name))

	}

	return origlen - len(buf), count, names

}