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Fixes: https://github.com/rust-lang/compiler-builtins/issues/837
The assembly is based on
- https://github.com/NetBSD/src/blob/20433927938987dd64c8f6aa46904b7aca3fa39e/lib/libm/arch/i387/s_floor.S
- https://github.com/NetBSD/src/blob/20433927938987dd64c8f6aa46904b7aca3fa39e/lib/libm/arch/i387/s_ceil.S
Which both state
/*
* Written by J.T. Conklin <jtc@NetBSD.org>.
* Public domain.
*/
Which I believe means we're good in terms of licensing.
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The `feature_detect` module is currently being built on all targets, but
the use of `AtomicU32` causes a problem if atomics are not available
(such as with `bpfel-unknown-none`). Gate this module behind
`target_has_atomic = "ptr"`.
The below now completes successfully:
cargo build -p compiler_builtins --target=bpfel-unknown-none -Z build-std=core
Fixes: https://github.com/rust-lang/compiler-builtins/issues/908
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Get performance closer to the glibc implementations by adding assembly
fma routines, with runtime feature detection so they are used even if
not compiled with `+fma` (as the distributed standard library is often
not). Glibc uses ifuncs, this implementation stores a function pointer
in an atomic.
Results of CPU flags are also cached in order to avoid repeating the
startup time in calls to different functions. The feature detection code
is a slightly simplified version of `std-detect`.
Musl sources were used as a reference [1].
Fixes: https://github.com/rust-lang/rust/issues/140452 once synced
[1]: https://github.com/bminor/musl/blob/c47ad25ea3b484e10326f933e927c0bc8cded3da/src/math/x32/fma.c
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This module is used for both i686 and x86-64.
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