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nora 2022-10-09 19:45:11 +02:00
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@ -36,41 +36,35 @@ for more details.
```rust
use std::collections::HashMap;
use std::convert::{TryFrom, TryInto};
use std::mem::ManuallyDrop;
use stuff::{StuffedPtr, StuffingStrategy};
use stuff::{StuffedPtr, StuffingStrategy, Unstuffed};
// Create a unit struct for our strategy
struct NanBoxStrategy;
// implementation detail of NaN boxing, a quiet NaN mask
const QNAN: u64 = 0x7ffc000000000000;
const QNAN: u64 = 0x7ffc000000000000;
// implementation detail of NaN boxing, the sign bit of an f64
const SIGN_BIT: u64 = 0x8000000000000000;
const SIGN_BIT: u64 = 0x8000000000000000;
unsafe impl StuffingStrategy<u64> for NanBoxStrategy {
impl StuffingStrategy<u64> for NanBoxStrategy {
type Other = f64;
fn is_other(data: u64) -> bool {
(data & QNAN) != QNAN
}
fn stuff_other(inner: Self::Other) -> u64 {
unsafe { std::mem::transmute(inner) } // both are 64 bit POD's
}
unsafe fn extract_other(data: u64) -> Self::Other {
std::mem::transmute(data) // both are 64 bit POD's
fn extract(data: u64) -> Unstuffed<usize, f64> {
if (data & QNAN) != QNAN {
Unstuffed::Other(f64::from_bits(data))
} else {
Unstuffed::Ptr((data & !(SIGN_BIT | QNAN)).try_into().unwrap())
}
}
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()
}
}
// a very, very crude representation of an object
@ -79,20 +73,19 @@ type Object = HashMap<String, u32>;
// our value type
type Value = StuffedPtr<Object, NanBoxStrategy, u64>;
fn main() {
let float: Value = StuffedPtr::new_other(123.5);
assert_eq!(float.copy_other(), Some(123.5));
let float: Value = StuffedPtr::new_other(123.5);
assert_eq!(float.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: 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));
let object = unsafe { &*ptr.ptr().unwrap() };
assert_eq!(object.get("a"), Some(&457));
drop(unsafe { Box::from_raw(ptr.get_ptr().unwrap()) });
// be careful, `ptr` is a dangling pointer now!
}
drop(unsafe { Box::from_raw(ptr.ptr().unwrap()) });
// be careful, `ptr` is a dangling pointer now!
```
# MSRV-Policy