Simplify bits_for_tags impl

rust-lang · Apr 20, 2023 · ad8c7b6 · ad8c7b6
1 parent 7cfecf2
commit ad8c7b6
Showing 1 changed file with 3 additions and 13 deletions.
diff --git a/compiler/rustc_data_structures/src/tagged_ptr.rs b/compiler/rustc_data_structures/src/tagged_ptr.rs
@@ -155,7 +155,9 @@ pub const fn bits_for_tags(mut tags: &[usize]) -> u32 {
  while let &[tag, ref rest @ ..] = tags {
  tags = rest;
 
- let b = bits_for_tag(tag);
+ // bits required to represent `tag`,
+ // position of the most significant 1
+ let b = usize::BITS - tag.leading_zeros();
  if b > bits {
  bits = b;
  }
@@ -164,18 +166,6 @@ pub const fn bits_for_tags(mut tags: &[usize]) -> u32 {
  bits
 }
 
-/// Returns `(size_of::<usize>() * 8) - tag.leading_zeros()`
-const fn bits_for_tag(mut tag: usize) -> u32 {
- let mut bits = 0;
-
- while tag > 0 {
- bits += 1;
- tag >>= 1;
- }
-
- bits
-}
-
 unsafe impl<T: ?Sized + Aligned> Pointer for Box<T> {
  const BITS: u32 = bits_for::<Self::Target>();