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rename extra to other

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this is a breaking change
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nora 2022-04-06 20:04:49 +02:00
parent 299e1613ff
commit bde74a68ba
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README.md
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@ -20,10 +20,10 @@ the user, allowing the user to do their bit stuffing only on integers (pointer a
`StuffedPtr` is the main type of this crate. It's a type whose size depends on the
choice of `Backend` (defaults to `usize`, `u64` and `u128` are also possible). It can store a
pointer or some extra data.
pointer or some `other` data.
You can choose any arbitrary bitstuffing depending on the `StuffingStrategy`, an unsafe trait that governs
how the extra data (or the pointer itself) will be packed into the backend. While this trait is still unsafe,
how the `other` data (or the pointer itself) will be packed into the backend. While this trait is still unsafe,
it's a lot safer than doing everything by hand.
# Example: NaN-Boxing
@ -36,59 +36,62 @@ for more details.
```rust
use std::collections::HashMap;
use stuff::{StuffedPtr, StuffingStrategy};
// Create a unit struct for our strategy
struct NanBoxStrategy;
const QNAN: u64 = 0x7ffc000000000000; // implementation detail of NaN boxing, a quiet NaN mask
const SIGN_BIT: u64 = 0x8000000000000000; // implementation detail of NaN boxing, the sign bit of an f64
// implementation detail of NaN boxing, a quiet NaN mask
const QNAN: u64 = 0x7ffc000000000000;
// implementation detail of NaN boxing, the sign bit of an f64
const SIGN_BIT: u64 = 0x8000000000000000;
unsafe impl StuffingStrategy<u64> for NanBoxStrategy {
type Extra = f64;
fn is_extra(data: u64) -> bool {
type Other = f64;
fn is_other(data: u64) -> bool {
(data & QNAN) != QNAN
}
fn stuff_extra(inner: Self::Extra) -> u64 {
fn stuff_other(inner: Self::Other) -> u64 {
unsafe { std::mem::transmute(inner) } // both are 64 bit POD's
}
unsafe fn extract_extra(data: u64) -> Self::Extra {
unsafe fn extract_other(data: u64) -> Self::Other {
std::mem::transmute(data) // both are 64 bit POD's
}
fn stuff_ptr(addr: usize) -> u64 {
// add the QNAN and SIGN_BIT
SIGN_BIT | QNAN | u64::try_from(addr).unwrap()
}
fn extract_ptr(inner: u64) -> usize {
// keep everything except for QNAN and SIGN_BIT
(inner & !(SIGN_BIT | QNAN)).try_into().unwrap()
}
}
type Object = HashMap<String, u32>; // a very, very crude representation of an object
// a very, very crude representation of an object
type Object = HashMap<String, u32>;
type Value = StuffedPtr<Object, NanBoxStrategy, u64>; // our value type
// our value type
type Value = StuffedPtr<Object, NanBoxStrategy, u64>;
fn main() {
let float: Value = StuffedPtr::new_extra(123.5);
assert_eq!(float.copy_extra(), Some(123.5));
let float: Value = StuffedPtr::new_other(123.5);
assert_eq!(float.copy_other(), Some(123.5));
let object: Object = HashMap::from([("a".to_owned(), 457)]);
let boxed = Box::new(object);
let ptr: Value = StuffedPtr::new_ptr(Box::into_raw(boxed));
let object = unsafe { &*ptr.get_ptr().unwrap() };
assert_eq!(object.get("a"), Some(&457));
drop(unsafe { Box::from_raw(ptr.get_ptr().unwrap()) });
// `ptr` is a dangling pointer now!
// be careful, `ptr` is a dangling pointer now!
}
```