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use rkyv::{
access_unchecked, deserialize,
rancor::{Error, Fallible},
ser::{Allocator, Writer},
vec::{ArchivedVec, VecResolver},
with::{ArchiveWith, DeserializeWith, SerializeWith},
Archive, Archived, Deserialize, Place, Serialize,
};
#[derive(Debug, PartialEq, Eq)]
pub enum Opcode {
// A 1-byte opcode
OneByte,
// A 2-byte opcode
TwoBytes(u8),
// A 3-byte opcode
ThreeBytes(u16),
// A 5-byte opcode
FiveBytes(u32),
// A 9-byte opcode
NineBytes(u64),
// A variable-length opcode
VariableLength(usize),
}
pub struct EncodeOpcodes;
pub struct OpcodesResolver {
len: usize,
inner: VecResolver,
}
impl ArchiveWith<Vec<Opcode>> for EncodeOpcodes {
type Archived = ArchivedVec<u8>;
type Resolver = OpcodesResolver;
fn resolve_with(
_: &Vec<Opcode>,
resolver: Self::Resolver,
out: Place<Self::Archived>,
) {
ArchivedVec::resolve_from_len(resolver.len, resolver.inner, out);
}
}
impl<S> SerializeWith<Vec<Opcode>, S> for EncodeOpcodes
where
S: Fallible + Allocator + Writer + ?Sized,
{
fn serialize_with(
field: &Vec<Opcode>,
serializer: &mut S,
) -> Result<Self::Resolver, S::Error> {
// Encode opcodes into a compact binary format
// We'll do it manually here, but you could just as easily proxy out to
// a serialization framework like postcard
let mut encoded = Vec::new();
for opcode in field.iter() {
match opcode {
Opcode::OneByte => encoded.push(0),
Opcode::TwoBytes(arg) => {
encoded.push(1);
encoded.extend(arg.to_le_bytes());
}
Opcode::ThreeBytes(arg) => {
encoded.push(2);
encoded.extend(arg.to_le_bytes());
}
Opcode::FiveBytes(arg) => {
encoded.push(3);
encoded.extend(arg.to_le_bytes());
}
Opcode::NineBytes(arg) => {
encoded.push(4);
encoded.extend(arg.to_le_bytes());
}
Opcode::VariableLength(arg) => {
let mut arg = *arg;
let bytes = arg.to_le_bytes();
let mut len = 1;
while arg >= 256 {
arg >>= 8;
len += 1;
}
encoded.push(4 + len as u8);
encoded.extend(&bytes[0..len]);
}
}
}
// Serialize encoded opcodes
Ok(OpcodesResolver {
len: encoded.len(),
inner: ArchivedVec::serialize_from_slice(
encoded.as_slice(),
serializer,
)?,
})
}
}
impl<D> DeserializeWith<Archived<Vec<u8>>, Vec<Opcode>, D> for EncodeOpcodes
where
D: Fallible + ?Sized,
{
fn deserialize_with(
field: &Archived<Vec<u8>>,
_: &mut D,
) -> Result<Vec<Opcode>, D::Error> {
let mut result = Vec::new();
// Decode opcodes from a compact binary format
let mut bytes = field.iter().cloned();
while let Some(op) = bytes.next() {
match op {
0 => result.push(Opcode::OneByte),
1 => {
let arg = bytes.next().unwrap();
result.push(Opcode::TwoBytes(arg));
}
2 => {
let arg = bytes.next().unwrap() as u16
| (bytes.next().unwrap() as u16) << 8;
result.push(Opcode::ThreeBytes(arg));
}
3 => {
let arg = bytes.next().unwrap() as u32
| (bytes.next().unwrap() as u32) << 8
| (bytes.next().unwrap() as u32) << 16
| (bytes.next().unwrap() as u32) << 24;
result.push(Opcode::FiveBytes(arg));
}
4 => {
let arg = bytes.next().unwrap() as u64
| (bytes.next().unwrap() as u64) << 8
| (bytes.next().unwrap() as u64) << 16
| (bytes.next().unwrap() as u64) << 24
| (bytes.next().unwrap() as u64) << 32
| (bytes.next().unwrap() as u64) << 40
| (bytes.next().unwrap() as u64) << 48
| (bytes.next().unwrap() as u64) << 56;
result.push(Opcode::NineBytes(arg));
}
n @ 5..=12 => {
let len = n - 4;
let mut arg = 0;
for i in 0..len {
arg |= (bytes.next().unwrap() as usize) << (8 * i);
}
result.push(Opcode::VariableLength(arg));
}
// Either the deserializer can be bound to support decode
// errors, or the opcodes can be checked during
// validation with bytecheck
_ => panic!("unexpected opcode"),
}
}
Ok(result)
}
}
#[derive(Archive, Serialize, Deserialize, Debug, PartialEq, Eq)]
pub struct Program {
#[rkyv(with = EncodeOpcodes)]
opcodes: Vec<Opcode>,
}
fn main() {
let program = Program {
opcodes: vec![
Opcode::OneByte,
Opcode::TwoBytes(42),
Opcode::ThreeBytes(27774),
Opcode::FiveBytes(31415926),
Opcode::NineBytes(123456789123456789),
Opcode::VariableLength(27774),
],
};
println!("opcodes: {:?}", program.opcodes);
let buf = rkyv::to_bytes::<Error>(&program).unwrap();
let archived_program = unsafe { access_unchecked::<ArchivedProgram>(&buf) };
println!("encoded: {:?}", archived_program.opcodes);
assert_eq!(archived_program.opcodes.len(), 23);
let deserialized_program =
deserialize::<Program, Error>(archived_program).unwrap();
println!("deserialized opcodes: {:?}", deserialized_program.opcodes);
assert_eq!(program, deserialized_program);
}
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