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header.rs
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header.rs
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// Copyright 2020 Google LLC
//
// 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::cell;
use std::mem::size_of;
use zerocopy::AsBytes;
use zerocopy::FromBytes;
use zerocopy::LayoutVerified;
pub type TypeSize = u32;
#[derive(Debug, Eq, PartialEq)]
#[allow(dead_code)] // We want a zero value to be defined.
pub enum Type {
// The table is empty. This is not explicitly used, but is a consequence
// of zero-initialization.
Empty = 0,
Root = 1,
Table = 2,
String = 3,
Unknown = 255,
}
impl From<TypeSize> for Type {
fn from(val: TypeSize) -> Type {
if val == Type::Empty as TypeSize {
return Type::Empty;
}
if val == Type::Root as TypeSize {
return Type::Root;
}
if val == Type::Table as TypeSize {
return Type::Table;
}
if val == Type::String as TypeSize {
return Type::String;
}
Type::Unknown
}
}
#[derive(Debug, AsBytes, FromBytes)]
#[repr(C)]
pub struct Root {
pub htype: TypeSize,
pad0: [u8; 4],
pub root_table_offset: usize,
pub string_offset: usize,
}
impl Root {
pub fn set_type(&mut self, t: Type) {
self.htype = t as TypeSize;
}
pub fn set_table_offset(&mut self, offset: usize) {
self.root_table_offset = offset;
}
pub fn set_string_offset(&mut self, offset: usize) {
self.string_offset = offset;
}
}
#[derive(AsBytes, FromBytes)]
#[repr(C)]
pub struct TableHeader {
pub htype: TypeSize,
pad0: [u8; 4],
// Number of bits in this table
pub bits: u8,
pad1: [u8; 7],
// Followed by payload of 2^bits copies of cell::Instance.
}
impl TableHeader {
pub fn set_bits(&mut self, bits: u8) {
assert!(bits <= 64);
self.htype = Type::Table as TypeSize;
self.bits = bits;
}
}
pub struct Table<'a> {
header: &'a TableHeader,
cells: &'a [cell::Instance],
}
impl<'a> Table<'a> {
// Overlays a table on top of this slice. Assumes it is initialized.
pub fn overlay(bytes: &'a [u8]) -> Table {
let (header, rest): (LayoutVerified<_, TableHeader>, _) =
LayoutVerified::new_from_prefix(bytes).unwrap();
let header = header.into_ref();
assert_eq!(Type::from(header.htype), Type::Table);
let elems = 1 << header.bits;
let size = elems * size_of::<cell::Instance>();
let cells = LayoutVerified::new_slice(&rest[..size]).unwrap();
let cells = cells.into_slice();
Table { header, cells }
}
pub fn cell(&'a self, index: usize) -> &'a cell::Instance {
&self.cells[index]
}
pub fn index(&self, key: u64) -> usize {
let bits = self.header.bits;
let bitmask: u64 = (1 << bits) - 1;
let index = key & bitmask;
index as usize
}
pub fn next_key(&self, key: u64) -> u64 {
key >> self.header.bits
}
pub fn decrement_bits(&self, remaining: usize) -> usize {
let bits_usize: usize = self.header.bits as usize;
if remaining < bits_usize {
return 0;
}
remaining - bits_usize
}
}
pub struct TableMut<'a> {
header: &'a mut TableHeader,
cells: &'a mut [cell::Instance],
}
impl<'a> TableMut<'a> {
// Initializes a table for 2^bits entries.
pub fn init(bits: u8, bytes: &'a mut [u8]) -> TableMut {
assert!(bits <= 64);
let bytes_len = bytes.len();
let (header, rest): (LayoutVerified<_, TableHeader>, _) =
LayoutVerified::new_from_prefix_zeroed(bytes).expect(&format!(
"TableMut::init layout verified: bits: {}, len: {}",
bits,
bytes_len,
));
let elems = 1 << bits;
let size = elems * size_of::<cell::Instance>();
let cells = LayoutVerified::new_slice_zeroed(&mut rest[..size]).unwrap();
let header = header.into_mut();
header.set_bits(bits);
let cells = cells.into_mut_slice();
TableMut { header, cells }
}
// Overlays a mutable table on top of this slice. Assumes it is initialized.
pub fn overlay_mut(bytes: &'a mut [u8]) -> TableMut {
let (header, rest): (LayoutVerified<_, TableHeader>, _) =
LayoutVerified::new_from_prefix(bytes).unwrap();
let header = header.into_mut();
assert_eq!(Type::from(header.htype), Type::Table);
let elems = 1 << header.bits;
let size = elems * size_of::<cell::Instance>();
let cells = LayoutVerified::new_slice(&mut rest[..size]).unwrap();
let cells = cells.into_mut_slice();
TableMut { header, cells }
}
pub fn cell_mut(&'a mut self, index: usize) -> &'a mut cell::Instance {
&mut self.cells[index]
}
pub fn index(&self, key: u64) -> usize {
let bits = self.header.bits;
let bitmask: u64 = (1 << bits) - 1;
let index = key & bitmask;
index as usize
}
pub fn next_key(&self, key: u64) -> u64 {
key >> self.header.bits
}
pub fn decrement_bits(&self, remaining: usize) -> usize {
let bits_usize: usize = self.header.bits as usize;
if remaining < bits_usize {
return 0;
}
remaining - bits_usize
}
}
#[derive(AsBytes, FromBytes)]
#[repr(C)]
pub struct String {
htype: u32,
pad0: [u8; 4],
len: usize,
// Followed by payload which ends with a '/0' byte.
}
#[derive(AsBytes, FromBytes)]
#[repr(C)]
pub struct Empty {
htype: u32,
pad0: [u8; 4],
}