Auto merge of #129721 - workingjubilee:rollup-y2o1mnp, r=workingjubilee

Rollup of 14 pull requests

Successful merges:

 - #128192 (rustc_target: Add various aarch64 features)
 - #129170 (Add an ability to convert between `Span` and `visit::Location`)
 - #129343 (Emit specific message for time<=0.3.35)
 - #129378 (Clean up cfg-gating of ProcessPrng extern)
 - #129401 (Partially stabilize `feature(new_uninit)`)
 - #129467 (derive(SmartPointer): assume pointee from the single generic and better error messages)
 - #129494 (format code in tests/ui/threads-sendsync)
 - #129617 (Update books)
 - #129673 (Add fmt::Debug to sync::Weak<T, A>)
 - #129683 (copysign with sign being a NaN can have non-portable results)
 - #129689 (Move `'tcx` lifetime off of impl and onto methods for `CrateMetadataRef`)
 - #129695 (Fix path to run clippy on rustdoc)
 - #129712 (Correct trusty targets to be tier 3)
 - #129715 (Update `compiler_builtins` to `0.1.123`)

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 8 insertions, 3 deletions

diff --git a/library/std/src/f128.rs b/library/std/src/f128.rs
index 506d708d0d2..b436fe9929c 100644
--- a/library/std/src/f128.rs
+++ b/library/std/src/f128.rs
@@ -250,9 +250,14 @@ impl f128 {
     ///
     /// Equal to `self` if the sign of `self` and `sign` are the same, otherwise equal to `-self`.
     /// If `self` is a NaN, then a NaN with the same payload as `self` and the sign bit of `sign` is
-    /// returned. Note, however, that conserving the sign bit on NaN across arithmetical operations
-    /// is not generally guaranteed. See [specification of NaN bit
-    /// patterns](primitive@f32#nan-bit-patterns) for more info.
+    /// returned.
+    ///
+    /// If `sign` is a NaN, then this operation will still carry over its sign into the result. Note
+    /// that IEEE 754 doesn't assign any meaning to the sign bit in case of a NaN, and as Rust
+    /// doesn't guarantee that the bit pattern of NaNs are conserved over arithmetic operations, the
+    /// result of `copysign` with `sign` being a NaN might produce an unexpected or non-portable
+    /// result. See the [specification of NaN bit patterns](primitive@f32#nan-bit-patterns) for more
+    /// info.
     ///
     /// # Examples
     ///