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authorRalf Jung <post@ralfj.de>2020-12-26 18:07:52 +0100
committerRalf Jung <post@ralfj.de>2020-12-26 18:07:52 +0100
commit8543388beb52785897b87e3f0a5ffd3c8560f956 (patch)
treecdb1fcdfee072d3893e6e530390446c59ab5c609
parent3533204e999cf70378131c63e1abbfe812109792 (diff)
downloadrust-8543388beb52785897b87e3f0a5ffd3c8560f956.tar.gz
rust-8543388beb52785897b87e3f0a5ffd3c8560f956.zip
address review feedback
-rw-r--r--library/core/src/ptr/const_ptr.rs35
-rw-r--r--library/core/src/ptr/mut_ptr.rs35
2 files changed, 40 insertions, 30 deletions
diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs
index 6638033566f..38519f759ae 100644
--- a/library/core/src/ptr/const_ptr.rs
+++ b/library/core/src/ptr/const_ptr.rs
@@ -238,10 +238,10 @@ 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
@@ -249,9 +249,10 @@ impl<T: ?Sized> *const T {
     /// 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.
@@ -580,10 +581,10 @@ 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
@@ -591,6 +592,8 @@ impl<T: ?Sized> *const T {
     /// 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.
     ///
@@ -643,10 +646,10 @@ 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
@@ -654,6 +657,8 @@ impl<T: ?Sized> *const T {
     /// 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
index a0edb036c25..92f4e431de4 100644
--- a/library/core/src/ptr/mut_ptr.rs
+++ b/library/core/src/ptr/mut_ptr.rs
@@ -244,10 +244,10 @@ 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
@@ -255,9 +255,10 @@ impl<T: ?Sized> *mut T {
     /// 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.
@@ -687,10 +688,10 @@ 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
@@ -698,6 +699,8 @@ impl<T: ?Sized> *mut T {
     /// 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.
     ///
@@ -750,10 +753,10 @@ 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
@@ -761,6 +764,8 @@ impl<T: ?Sized> *mut T {
     /// 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.
     ///