impl more traits for ptr::Alignment, add mask method

Author: clarfonthey

library/core/src/ptr/alignment.rs

@@ -1,7 +1,7 @@
 use crate::convert::{TryFrom, TryInto};
 use crate::intrinsics::assert_unsafe_precondition;
 use crate::num::NonZeroUsize;
-use crate::{cmp, fmt, hash, mem, num};
+use crate::{cmp, fmt, hash, mem, num, str};
 
 /// A type storing a `usize` which is a power of two, and thus
 /// represents a possible alignment in the rust abstract machine.
@@ -42,6 +42,7 @@ impl Alignment {
     /// This provides the same numerical value as [`mem::align_of`],
     /// but in an `Alignment` instead of a `usize`.
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
     pub const fn of<T>() -> Self {
         // SAFETY: rustc ensures that type alignment is always a power of two.
@@ -53,6 +54,7 @@ impl Alignment {
     ///
     /// Note that `0` is not a power of two, nor a valid alignment.
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
     pub const fn new(align: usize) -> Option<Self> {
         if align.is_power_of_two() {
@@ -98,6 +100,7 @@ impl Alignment {
 
     /// Returns the alignment as a [`NonZeroUsize`]
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
     pub const fn as_nonzero(self) -> NonZeroUsize {
         // SAFETY: All the discriminants are non-zero.
@@ -118,10 +121,39 @@ impl Alignment {
     /// assert_eq!(Alignment::new(1024).unwrap().log2(), 10);
     /// ```
     #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
     #[inline]
-    pub fn log2(self) -> u32 {
+    pub const fn log2(self) -> u32 {
         self.as_nonzero().trailing_zeros()
     }
+
+    /// Returns a bit mask that can be used to match this alignment.
+    ///
+    /// This is equivalent to `!(self.as_usize() - 1)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ptr_alignment_type)]
+    /// #![feature(ptr_mask)]
+    /// use std::ptr::{Alignment, NonNull};
+    ///
+    /// let one = <NonNull<u8>>::dangling().as_ptr();
+    /// let four = <NonNull<u32>>::dangling().as_ptr();
+    ///
+    /// assert_eq!(four.mask(Alignment::of::<u8>().mask()), four);
+    /// assert_eq!(four.mask(Alignment::of::<u16>().mask()), four);
+    /// assert_eq!(four.mask(Alignment::of::<u32>().mask()), four);
+    /// assert_ne!(four.mask(Alignment::of::<u64>().mask()), four);
+    /// assert_ne!(one.mask(Alignment::of::<u64>().mask()), one);
+    /// ```
+    #[unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[rustc_const_unstable(feature = "ptr_alignment_type", issue = "102070")]
+    #[inline]
+    pub const fn mask(self) -> usize {
+        // SAFETY: The alignment is always nonzero, and therefore decrementing won't overflow.
+        !(unsafe { self.as_usize().unchecked_sub(1) })
+    }
 }
 
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
@@ -131,6 +163,92 @@ impl fmt::Debug for Alignment {
     }
 }
 
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::Display for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.as_nonzero(), f)
+    }
+}
+
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::Binary for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Binary::fmt(&self.as_nonzero(), f)
+    }
+}
+
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::Octal for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Octal::fmt(&self.as_nonzero(), f)
+    }
+}
+
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::LowerHex for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.as_nonzero(), f)
+    }
+}
+
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::UpperHex for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::UpperHex::fmt(&self.as_nonzero(), f)
+    }
+}
+
+impl Alignment {
+    // longest string: 1p-128
+    fn fmt_exp(self, buf: &mut [u8; 6], p: u8) -> &[u8] {
+        buf[0] = b'1';
+        buf[1] = p;
+
+        let mut shl = self.log2() as u8;
+        if shl == 0 {
+            buf[2] = b'0';
+            return &buf[..3];
+        }
+
+        buf[2] = b'-';
+        if shl > 100 {
+            buf[5] = b'0' + shl % 10;
+            shl /= 10;
+            buf[4] = b'0' + shl % 10;
+            shl /= 10;
+            buf[3] = b'0' + shl % 10;
+            &buf[..6]
+        } else if shl > 10 {
+            buf[4] = b'0' + shl % 10;
+            shl /= 10;
+            buf[3] = b'0' + shl % 10;
+            &buf[..5]
+        } else {
+            buf[3] = b'0' + shl % 10;
+            &buf[..4]
+        }
+    }
+}
+
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::LowerExp for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut buf = [0; 6];
+
+        // SAFETY: We generate an ASCII string, which is valid UTF-8.
+        f.pad(unsafe { str::from_utf8_unchecked(self.fmt_exp(&mut buf, b'p')) })
+    }
+}
+
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl fmt::UpperExp for Alignment {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut buf = [0; 6];
+        // SAFETY: We generate an ASCII string, which is valid UTF-8.
+        f.pad(unsafe { str::from_utf8_unchecked(self.fmt_exp(&mut buf, b'P')) })
+    }
+}
+
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
 impl TryFrom<NonZeroUsize> for Alignment {
     type Error = num::TryFromIntError;
@@ -193,6 +311,13 @@ impl hash::Hash for Alignment {
     }
 }
 
+#[unstable(feature = "ptr_alignment_type", issue = "102070")]
+impl Default for Alignment {
+    fn default() -> Alignment {
+        Alignment::MIN
+    }
+}
+
 #[cfg(target_pointer_width = "16")]
 type AlignmentEnum = AlignmentEnum16;
 #[cfg(target_pointer_width = "32")]

library/core/tests/lib.rs

@@ -115,6 +115,7 @@
 #![feature(get_many_mut)]
 #![feature(offset_of)]
 #![feature(iter_map_windows)]
+#![feature(ptr_alignment_type)]
 #![deny(unsafe_op_in_unsafe_fn)]
 #![deny(fuzzy_provenance_casts)]
 

library/core/tests/ptr.rs

@@ -1126,3 +1126,13 @@ fn test_const_copy() {
         assert!(*ptr2 == 1);
     };
 }
+
+#[test]
+fn alignment_exp_formatting() {
+    let p0 = Alignment::MIN;
+    let p1 = Alignment::new(2).unwrap();
+    let p42 = Alignment::new(1 << 42).unwrap();
+    assert_eq!(format!("{:e}", p0), "1p0");
+    assert_eq!(format!("{:E}", p1), "1P-1");
+    assert_eq!(format!("{:e}", p42), "1p-42");
+}

tests/ui/fmt/ifmt-unimpl.stderr

@@ -15,7 +15,7 @@ LL |     format!("{:X}", "3");
              i128
              usize
              u8
-           and 20 others
+           and 21 others
    = note: required for `&str` to implement `UpperHex`
 note: required by a bound in `core::fmt::rt::Argument::<'a>::new_upper_hex`
   --> $SRC_DIR/core/src/fmt/rt.rs:LL:COL