ccache 0.1.0

Composable Caches
Documentation 
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/*
 * Copyright 2021 Luca Fulchir <luker@fenrirproject.org>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use crate::hashmap::user;

// TODO: implement small counter optimization

// We only have two generations to keep track of.
// There is no "new" and "old" generation, since
// every X queries the "old" will become the "new"
// The naming should not give old/new ideas
#[derive(PartialEq, Eq, Copy, Clone)]
pub enum Generation {
    Day,
    Night,
}
impl ::std::ops::Not for Generation {
    type Output = Self;
    fn not(self) -> Self::Output {
        match self {
            Generation::Day => Generation::Night,
            Generation::Night => Generation::Day,
        }
    }
}
impl From<bool> for Generation {
    fn from(is_night: bool) -> Self {
        match is_night {
            false => Generation::Day,
            true => Generation::Night,
        }
    }
}
impl From<Generation> for bool {
    fn from(g: Generation) -> Self {
        match g {
            Generation::Day => false,
            Generation::Night => true,
        }
    }
}
impl Default for Generation {
    fn default() -> Self {
        Generation::Day
    }
}

pub trait CidCounter<Cid>: user::Cid
where
    Cid: user::Cid,
{
    fn new(cid: Cid) -> Self;
    fn get_cid(&self) -> Cid;
    fn set_cid(&mut self, cid: Cid);

    fn get_generation(&self) -> Generation;
    fn flip_generation(&mut self);

    fn get_counter(&self) -> u32;
    fn add(&mut self);
    fn halve(&mut self);
}

#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum WTLFUCid {
    None = 0,
    Window = 1,
    SLRUProbation = 2,
    SLRUProtected = 3,
}
impl Default for WTLFUCid {
    fn default() -> Self {
        WTLFUCid::None
    }
}
impl user::Cid for WTLFUCid {}
impl From<u8> for WTLFUCid {
    fn from(raw: u8) -> Self {
        match raw {
            0 => WTLFUCid::None,
            1 => WTLFUCid::Window,
            2 => WTLFUCid::SLRUProbation,
            3 => WTLFUCid::SLRUProtected,
            _ => {
                ::std::panic!("No such binary repr of WTLFUCid")
            }
        }
    }
}

// This is a Cid, but it hides generation and counters inside
// make sure it behaves as a Cid first and foremost
::bitfield::bitfield! {
    #[derive(Copy, Clone)]
    pub struct Full32(u32);
    impl Debug;
    #[inline]
    pub u8, into WTLFUCid, g_cid, s_cid: 2, 0;
    #[inline]
    pub into Generation, g_generation, s_generation: 0;
    #[inline]
    pub u32, g_counter, s_counter: 29, 0;
}
impl user::Cid for Full32 {}

impl Default for Full32 {
    fn default() -> Self {
        Full32(0)
    }
}
impl PartialEq for Full32 {
    fn eq(&self, other: &Self) -> bool {
        self.g_cid() == other.g_cid()
    }
}
impl Eq for Full32 {}

impl CidCounter<WTLFUCid> for Full32 {
    fn new(cid: WTLFUCid) -> Self {
        let mut res = Full32::default();
        res.set_cid(cid);
        res
    }
    fn get_cid(&self) -> WTLFUCid {
        self.g_cid()
    }
    fn set_cid(&mut self, cid: WTLFUCid) {
        self.s_cid(cid as u8)
    }

    fn get_generation(&self) -> Generation {
        self.g_generation().into()
    }
    fn flip_generation(&mut self) {
        match self.g_generation().into() {
            Generation::Day => self.s_generation(Generation::Night.into()),
            Generation::Night => self.s_generation(Generation::Day.into()),
        }
    }

    fn get_counter(&self) -> u32 {
        self.g_counter()
    }
    fn add(&mut self) {
        let tmp = self.g_counter();
        self.s_counter(tmp + 1);
    }
    fn halve(&mut self) {
        let tmp = self.g_counter();
        self.s_counter(tmp / 2);
    }
}