From 906019f7c6efa5984dba8ff34a62578be50c9dac Mon Sep 17 00:00:00 2001
From: dzy <daizy15@mails.tsinghua.edu.cn>
Date: Fri, 7 Sep 2018 20:53:37 +0800
Subject: [PATCH] Add little notes for BitAllocator

---
 crate/bit-allocator/src/lib.rs | 15 +++++++++++++++
 crate/process/src/scheduler.rs |  3 ++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/crate/bit-allocator/src/lib.rs b/crate/bit-allocator/src/lib.rs
index bc49dcb3..02c38c2c 100644
--- a/crate/bit-allocator/src/lib.rs
+++ b/crate/bit-allocator/src/lib.rs
@@ -6,6 +6,18 @@ extern crate bit_field;
 use bit_field::BitField;
 use core::ops::Range;
 
+/// Allocator of a bitmap, able to allocate / free bits.
+///
+/// CAP: the bitmap has a total of CAP bits, numbered from 0 to CAP-1 inclusively.
+///
+/// alloc: allocate a free bit.
+/// dealloc: free an allocated bit.
+///
+/// insert: mark bits in the range as allocated
+/// remove: reverse of insert
+///
+/// any: whether there are free bits remaining
+/// test: whether a specific bit is free
 pub trait BitAlloc: Default {
     const CAP: usize;
     fn alloc(&mut self) -> Option<usize>;
@@ -23,6 +35,7 @@ pub type BitAlloc1M = BitAllocCascade16<BitAlloc64K>;
 pub type BitAlloc16M = BitAllocCascade16<BitAlloc1M>;
 pub type BitAlloc256M = BitAllocCascade16<BitAlloc16M>;
 
+/// Implement the bit allocator by segment tree algorithm.
 #[derive(Default)]
 pub struct BitAllocCascade16<T: BitAlloc> {
     bitset: u16,
@@ -77,6 +90,8 @@ impl<T: BitAlloc> BitAllocCascade16<T> {
 #[derive(Default)]
 pub struct BitAlloc16(u16);
 
+/// BitAlloc16 acts as the leaf (except the leaf bits of course) nodes
+/// in the segment trees.
 impl BitAlloc for BitAlloc16 {
     const CAP: usize = 16;
 
diff --git a/crate/process/src/scheduler.rs b/crate/process/src/scheduler.rs
index f29df1f6..4d8e6964 100644
--- a/crate/process/src/scheduler.rs
+++ b/crate/process/src/scheduler.rs
@@ -211,4 +211,5 @@ mod stride {
 fn expand<T: Default + Clone>(vec: &mut Vec<T>, id: usize) {
     let len = vec.len();
     vec.resize(len.max(id + 1), T::default());
-}
\ No newline at end of file
+}
+