address review feedback

rust-lang · bors · Dec 29, 2020 · Dec 26, 2020 · Dec 26, 2020 · Dec 17, 2020
commit 8543388beb52785897b87e3f0a5ffd3c8560f956
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
@@ -238,20 +238,21 @@ impl<T: ?Sized> *const T {
     /// It may *not* be used to access a different allocated object. Note that in Rust, every
     /// (stack-allocated) variable is considered a separate allocated object.
     ///
-    /// In other words, `let z = x.wrapping_add((y as usize).wrapping_sub(x as usize) /
-    /// size_of::<T>())` does *not* make `z` the same as `y`: `z` is still attached to the object `x` is
-    /// attached to, and dereferencing it is Undefined Behavior unless `x` and `y` point into the
-    /// same allocated object.
+    /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
+    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
+    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
+    /// `x` and `y` point into the same allocated object.
     ///
     /// Compared to [`offset`], this method basically delays the requirement of staying within the
     /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
     /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
     /// can be optimized better and is thus preferable in performance-sensitive code.
     ///
-    /// `x.wrapping_offset(o).wrapping_offset(-o)` is always the same as `x` (if `-o` does not
-    /// overflow). In other words, leaving the allocated object and then re-entering it later is
-    /// permitted.
+    /// The delayed check only considers the value of the pointer that was dereferenced, not the
+    /// intermediate values used during the computation of the final result. For example,
+    /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
+    /// words, leaving the allocated object and then re-entering it later is permitted.
     ///
     /// If you need to cross object boundaries, cast the pointer to an integer and
     /// do the arithmetic there.
@@ -580,17 +581,19 @@ impl<T: ?Sized> *const T {
     /// It may *not* be used to access a different allocated object. Note that in Rust, every
     /// (stack-allocated) variable is considered a separate allocated object.
     ///
-    /// In other words, `let z = x.wrapping_add((y as usize).wrapping_sub(x as usize) /
-    /// size_of::<T>())` does *not* make `z` the same as `y`: `z` is still attached to the object `x` is
-    /// attached to, and dereferencing it is Undefined Behavior unless `x` and `y` point into the
-    /// same allocated object.
+    /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
+    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
+    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
+    /// `x` and `y` point into the same allocated object.
     ///
     /// Compared to [`add`], this method basically delays the requirement of staying within the
    /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
     /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
     /// can be optimized better and is thus preferable in performance-sensitive code.
     ///
+    /// The delayed check only considers the value of the pointer that was dereferenced, not the
+    /// intermediate values used during the computation of the final result. For example,
     /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
     /// allocated object and then re-entering it later is permitted.
     ///
@@ -643,17 +646,19 @@ impl<T: ?Sized> *const T {
     /// It may *not* be used to access a different allocated object. Note that in Rust, every
     /// (stack-allocated) variable is considered a separate allocated object.
     ///
-    /// In other words, `let z = x.wrapping_add((y as usize).wrapping_sub(x as usize) /
-    /// size_of::<T>())` does *not* make `z` the same as `y`: `z` is still attached to the object `x` is
-    /// attached to, and dereferencing it is Undefined Behavior unless `x` and `y` point into the
-    /// same allocated object.
+    /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
+    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
+    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
+    /// `x` and `y` point into the same allocated object.
     ///
     /// Compared to [`sub`], this method basically delays the requirement of staying within the
     /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
     /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
     /// can be optimized better and is thus preferable in performance-sensitive code.
     ///
+    /// The delayed check only considers the value of the pointer that was dereferenced, not the
+    /// intermediate values used during the computation of the final result. For example,
     /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
     /// allocated object and then re-entering it later is permitted.
     ///

diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs
@@ -244,20 +244,21 @@ impl<T: ?Sized> *mut T {
     /// It may *not* be used to access a different allocated object. Note that in Rust, every
     /// (stack-allocated) variable is considered a separate allocated object.
     ///
-    /// In other words, `let z = x.wrapping_add((y as usize).wrapping_sub(x as usize) /
-    /// size_of::<T>())` does *not* make `z` the same as `y`: `z` is still attached to the object `x` is
-    /// attached to, and dereferencing it is Undefined Behavior unless `x` and `y` point into the
-    /// same allocated object.
+    /// In other words, `let z = x.wrapping_offset((y as isize) - (x as isize))` does *not* make `z`
+    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
+    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
+    /// `x` and `y` point into the same allocated object.
     ///
     /// Compared to [`offset`], this method basically delays the requirement of staying within the
     /// same allocated object: [`offset`] is immediate Undefined Behavior when crossing object
     /// boundaries; `wrapping_offset` produces a pointer but still leads to Undefined Behavior if a
     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`offset`]
     /// can be optimized better and is thus preferable in performance-sensitive code.
     ///
-    /// `x.wrapping_offset(o).wrapping_offset(-o)` is always the same as `x` (if `-o` does not
-    /// overflow). In other words, leaving the allocated object and then re-entering it later is
-    /// permitted.
+    /// The delayed check only considers the value of the pointer that was dereferenced, not the
+    /// intermediate values used during the computation of the final result. For example,
+    /// `x.wrapping_offset(o).wrapping_offset(o.wrapping_neg())` is always the same as `x`. In other
+    /// words, leaving the allocated object and then re-entering it later is permitted.
     ///
     /// If you need to cross object boundaries, cast the pointer to an integer and
     /// do the arithmetic there.
@@ -687,17 +688,19 @@ impl<T: ?Sized> *mut T {
     /// It may *not* be used to access a different allocated object. Note that in Rust, every
     /// (stack-allocated) variable is considered a separate allocated object.
     ///
-    /// In other words, `let z = x.wrapping_add((y as usize).wrapping_sub(x as usize) /
-    /// size_of::<T>())` does *not* make `z` the same as `y`: `z` is still attached to the object `x` is
-    /// attached to, and dereferencing it is Undefined Behavior unless `x` and `y` point into the
-    /// same allocated object.
+    /// In other words, `let z = x.wrapping_add((y as usize) - (x as usize))` does *not* make `z`
+    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
+    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
+    /// `x` and `y` point into the same allocated object.
     ///
     /// Compared to [`add`], this method basically delays the requirement of staying within the
     /// same allocated object: [`add`] is immediate Undefined Behavior when crossing object
     /// boundaries; `wrapping_add` produces a pointer but still leads to Undefined Behavior if a
     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`add`]
     /// can be optimized better and is thus preferable in performance-sensitive code.
     ///
+    /// The delayed check only considers the value of the pointer that was dereferenced, not the
+    /// intermediate values used during the computation of the final result. For example,
     /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
     /// allocated object and then re-entering it later is permitted.
     ///
@@ -750,17 +753,19 @@ impl<T: ?Sized> *mut T {
     /// It may *not* be used to access a different allocated object. Note that in Rust, every
     /// (stack-allocated) variable is considered a separate allocated object.
     ///
-    /// In other words, `let z = x.wrapping_add((y as usize).wrapping_sub(x as usize) /
-    /// size_of::<T>())` does *not* make `z` the same as `y`: `z` is still attached to the object `x` is
-    /// attached to, and dereferencing it is Undefined Behavior unless `x` and `y` point into the
-    /// same allocated object.
+    /// In other words, `let z = x.wrapping_sub((x as usize) - (y as usize))` does *not* make `z`
+    /// the same as `y` even if we assume `T` has size `1` and there is no overflow: `z` is still
+    /// attached to the object `x` is attached to, and dereferencing it is Undefined Behavior unless
+    /// `x` and `y` point into the same allocated object.
     ///
     /// Compared to [`sub`], this method basically delays the requirement of staying within the
     /// same allocated object: [`sub`] is immediate Undefined Behavior when crossing object
     /// boundaries; `wrapping_sub` produces a pointer but still leads to Undefined Behavior if a
     /// pointer is dereferenced when it is out-of-bounds of the object it is attached to. [`sub`]
     /// can be optimized better and is thus preferable in performance-sensitive code.
     ///
+    /// The delayed check only considers the value of the pointer that was dereferenced, not the
+    /// intermediate values used during the computation of the final result. For example,
     /// `x.wrapping_add(o).wrapping_sub(o)` is always the same as `x`. In other words, leaving the
     /// allocated object and then re-entering it later is permitted.
     ///