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Avoid latent (harmless) overflow in core::slice.

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This overflow does not cause any problems; it just causes errors to be
signalled when compiling with `-C debug-assertions`.

Fix #24997
This commit is contained in:
Felix S. Klock II 2015-05-01 01:00:48 +02:00
parent f9ecc6e888
commit 42cb2de139
1 changed files with 24 additions and 6 deletions
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30
src/libcore/slice.rs
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@ -631,8 +631,14 @@ fn size_from_ptr<T>(_: *const T) -> usize {
}
// Use macro to be generic over const/mut
macro_rules! slice_offset {
// Use macros to be generic over const/mut
//
// They require non-negative `$by` because otherwise the expression
// `(ptr as usize + $by)` would interpret `-1` as `usize::MAX` (and
// thus trigger a panic when overflow checks are on).
// Use this to do `$ptr + $by`, where `$by` is non-negative.
macro_rules! slice_add_offset {
($ptr:expr, $by:expr) => {{
let ptr = $ptr;
if size_from_ptr(ptr) == 0 {
@ -643,6 +649,18 @@ macro_rules! slice_offset {
}};
}
// Use this to do `$ptr - $by`, where `$by` is non-negative.
macro_rules! slice_sub_offset {
($ptr:expr, $by:expr) => {{
let ptr = $ptr;
if size_from_ptr(ptr) == 0 {
transmute(ptr as usize - $by)
} else {
ptr.offset(-$by)
}
}};
}
macro_rules! slice_ref {
($ptr:expr) => {{
let ptr = $ptr;
@ -672,7 +690,7 @@ macro_rules! iterator {
None
} else {
let old = self.ptr;
self.ptr = slice_offset!(self.ptr, 1);
self.ptr = slice_add_offset!(self.ptr, 1);
Some(slice_ref!(old))
}
}
@ -714,7 +732,7 @@ macro_rules! iterator {
if self.end == self.ptr {
None
} else {
self.end = slice_offset!(self.end, -1);
self.end = slice_sub_offset!(self.end, 1);
Some(slice_ref!(self.end))
}
}
@ -816,7 +834,7 @@ impl<'a, T> Iter<'a, T> {
fn iter_nth(&mut self, n: usize) -> Option<&'a T> {
match self.as_slice().get(n) {
Some(elem_ref) => unsafe {
self.ptr = slice_offset!(elem_ref as *const _, 1);
self.ptr = slice_add_offset!(elem_ref as *const _, 1);
Some(slice_ref!(elem_ref))
},
None => {
@ -959,7 +977,7 @@ impl<'a, T> IterMut<'a, T> {
fn iter_nth(&mut self, n: usize) -> Option<&'a mut T> {
match make_mut_slice!(T => &'a mut [T]: self.ptr, self.end).get_mut(n) {
Some(elem_ref) => unsafe {
self.ptr = slice_offset!(elem_ref as *mut _, 1);
self.ptr = slice_add_offset!(elem_ref as *mut _, 1);
Some(slice_ref!(elem_ref))
},
None => {