//go:build unix

package mem

import (
	"syscall"
	"unsafe"
)

func reserve(total_address_space uintptr) ([]byte, error) {
	data, err := syscall.Mmap(-1, 0, int(total_address_space), syscall.PROT_NONE, syscall.MAP_PRIVATE|syscall.MAP_ANON)
	if err != nil {
		return nil, err
	}

	return data, nil
}

func release(reserved []byte) error {
	return syscall.Munmap(reserved)
}

func commit(reserved []byte, access Access) error {
	return syscall.Mprotect(reserved, access_to_prot(access))
}

func decommit(committed []byte) (err error) {
	err = syscall.Mprotect(committed, syscall.PROT_NONE)
	if err != nil {
		return
	}

	return madvise(committed, syscall.MADV_DONTNEED)
}

var _zero uintptr

func madvise(b []byte, advice int) (err error) {
	var _p0 unsafe.Pointer
	if len(b) > 0 {
		_p0 = unsafe.Pointer(&b[0])
	} else {
		_p0 = unsafe.Pointer(&_zero)
	}

	_, _, e := syscall.Syscall(syscall.SYS_MADVISE, uintptr(_p0), uintptr(len(b)), uintptr(advice))
	if e != 0 {
		err = syscall.Errno(e)
	}

	return
}

func access_to_prot(access Access) (prot int) {
	prot = syscall.PROT_NONE

	if access&AccessRead != 0 {
		prot |= syscall.PROT_READ
	}
	if access&AccessWrite != 0 {
		prot |= syscall.PROT_WRITE
	}
	if access&AccessExecute != 0 {
		prot |= syscall.PROT_EXEC
	}

	return
}