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Add a disclaimer about x86 f128 math functions

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Due to a LLVM bug, `f128` math functions link successfully but LLVM
chooses the wrong symbols (`long double` symbols rather than those for
binary128).

Since this is a notable problem that may surprise a number of users, add
a note about it.

Link: https://github.com/llvm/llvm-project/issues/44744
This commit is contained in:
Trevor Gross 2024-07-30 18:11:46 -04:00
parent 43836421f8
commit 8e2ca0c9d5
1 changed files with 3 additions and 0 deletions
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3
library/core/src/primitive_docs.rs
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@ -1244,6 +1244,9 @@ mod prim_f64 {}
/// actually implement it. For x86-64 and AArch64, ISA support is not even specified,
/// so it will always be a software implementation significantly slower than `f64`.
///
/// _Note: `f128` support is incomplete. Many platforms will not be able to link math functions. On
/// x86 in particular, these functions do link but their results are always incorrect._
///
/// *[See also the `std::f128::consts` module](crate::f128::consts).*
///
/// [wikipedia]: https://en.wikipedia.org/wiki/Quadruple-precision_floating-point_format