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use crate::stacked_borrows::SbTag;
use std::fmt;
use std::num::NonZeroU64;
#[derive(Copy, Clone, Hash, PartialEq, Eq)]
pub struct Item(u64);
const TAG_MASK: u64 = u64::MAX >> 3;
const PERM_MASK: u64 = 0x3 << 61;
const PROTECTED_MASK: u64 = 0x1 << 63;
const PERM_SHIFT: u64 = 61;
const PROTECTED_SHIFT: u64 = 63;
impl Item {
pub fn new(tag: SbTag, perm: Permission, protected: bool) -> Self {
assert!(tag.0.get() <= TAG_MASK);
let packed_tag = tag.0.get();
let packed_perm = perm.to_bits() << PERM_SHIFT;
let packed_protected = u64::from(protected) << PROTECTED_SHIFT;
let new = Self(packed_tag | packed_perm | packed_protected);
debug_assert!(new.tag() == tag);
debug_assert!(new.perm() == perm);
debug_assert!(new.protected() == protected);
new
}
pub fn tag(self) -> SbTag {
SbTag(NonZeroU64::new(self.0 & TAG_MASK).unwrap())
}
pub fn perm(self) -> Permission {
Permission::from_bits((self.0 & PERM_MASK) >> PERM_SHIFT)
}
pub fn protected(self) -> bool {
self.0 & PROTECTED_MASK > 0
}
pub fn set_permission(&mut self, perm: Permission) {
self.0 &= !PERM_MASK;
self.0 |= perm.to_bits() << PERM_SHIFT;
}
}
impl fmt::Debug for Item {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "[{:?} for {:?}]", self.perm(), self.tag())
}
}
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
pub enum Permission {
Unique,
SharedReadWrite,
SharedReadOnly,
Disabled,
}
impl Permission {
const UNIQUE: u64 = 0;
const SHARED_READ_WRITE: u64 = 1;
const SHARED_READ_ONLY: u64 = 2;
const DISABLED: u64 = 3;
fn to_bits(self) -> u64 {
match self {
Permission::Unique => Self::UNIQUE,
Permission::SharedReadWrite => Self::SHARED_READ_WRITE,
Permission::SharedReadOnly => Self::SHARED_READ_ONLY,
Permission::Disabled => Self::DISABLED,
}
}
fn from_bits(perm: u64) -> Self {
match perm {
Self::UNIQUE => Permission::Unique,
Self::SHARED_READ_WRITE => Permission::SharedReadWrite,
Self::SHARED_READ_ONLY => Permission::SharedReadOnly,
Self::DISABLED => Permission::Disabled,
_ => unreachable!(),
}
}
}