70 lines
1.9 KiB
Rust
70 lines
1.9 KiB
Rust
use std::{mem, ptr};
|
|
|
|
fn main() {
|
|
test_offset_from();
|
|
test_vec_into_iter();
|
|
ptr_arith_offset();
|
|
ptr_arith_offset_overflow();
|
|
ptr_offset();
|
|
}
|
|
|
|
fn test_offset_from() { unsafe {
|
|
let buf = [0u32; 4];
|
|
|
|
let x = buf.as_ptr() as *const u8;
|
|
let y = x.offset(12);
|
|
|
|
assert_eq!(y.offset_from(x), 12);
|
|
assert_eq!(x.offset_from(y), -12);
|
|
assert_eq!((y as *const u32).offset_from(x as *const u32), 12/4);
|
|
assert_eq!((x as *const u32).offset_from(y as *const u32), -12/4);
|
|
|
|
let x = (((x as usize) * 2) / 2) as *const u8;
|
|
assert_eq!(y.offset_from(x), 12);
|
|
assert_eq!(x.offset_from(y), -12);
|
|
} }
|
|
|
|
// This also internally uses offset_from.
|
|
fn test_vec_into_iter() {
|
|
let v = Vec::<i32>::new();
|
|
let i = v.into_iter();
|
|
i.size_hint();
|
|
}
|
|
|
|
fn ptr_arith_offset() {
|
|
let v = [1i16, 2];
|
|
let x = &v as *const [i16] as *const i16;
|
|
let x = x.wrapping_offset(1);
|
|
assert_eq!(unsafe { *x }, 2);
|
|
}
|
|
|
|
fn ptr_arith_offset_overflow() {
|
|
let v = [1i16, 2];
|
|
let x = &mut ptr::null(); // going through memory as there are more sanity checks along that path
|
|
*x = v.as_ptr().wrapping_offset(1); // ptr to the 2nd element
|
|
// Adding 2*isize::max and then 1 is like substracting 1
|
|
*x = x.wrapping_offset(isize::MAX);
|
|
*x = x.wrapping_offset(isize::MAX);
|
|
*x = x.wrapping_offset(1);
|
|
assert_eq!(unsafe { **x }, 1);
|
|
}
|
|
|
|
fn ptr_offset() {
|
|
fn f() -> i32 { 42 }
|
|
|
|
let v = [1i16, 2];
|
|
let x = &v as *const [i16; 2] as *const i16;
|
|
let x = unsafe { x.offset(1) };
|
|
assert_eq!(unsafe { *x }, 2);
|
|
|
|
// fn ptr offset
|
|
unsafe {
|
|
let p = f as fn() -> i32 as usize;
|
|
let x = (p as *mut u32).offset(0) as usize;
|
|
// *cast* to ptr, then transmute to fn ptr.
|
|
// (transmuting int to [fn]ptr causes trouble.)
|
|
let f: fn() -> i32 = mem::transmute(x as *const ());
|
|
assert_eq!(f(), 42);
|
|
}
|
|
}
|