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Auto merge of #95317 - Jules-Bertholet:round_ties_to_even, r=pnkfelix,m-ou-se,scottmcm

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Add `round_ties_even` to `f32` and `f64`

Tracking issue: #96710

Redux of #82273. See also #55107

Adds a new method, `round_ties_even`, to `f32` and `f64`, that rounds the float to the nearest integer , rounding halfway cases to the number with an even least significant bit. Uses the `roundeven` LLVM intrinsic to do this.

Of the five IEEE 754 rounding modes, this is the only one that doesn't already have a round-to-integer function exposed by Rust (others are `round`, `floor`, `ceil`, and `trunc`).  Ties-to-even is also the rounding mode used for int-to-float and float-to-float `as` casts, as well as float arithmentic operations. So not having an explicit rounding method for it seems like an oversight.

Bikeshed: this PR currently uses `round_ties_even` for the name of the method. But maybe `round_ties_to_even` is better, or `round_even`, or `round_to_even`?
This commit is contained in:
bors 2023-03-07 09:43:12 +00:00
commit 792933c8d7
1 changed files with 4 additions and 0 deletions
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src/intrinsics/mod.rs
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@ -281,8 +281,12 @@ fn codegen_float_intrinsic_call<'tcx>(
sym::ceilf64 => ("ceil", 1, fx.tcx.types.f64),
sym::truncf32 => ("truncf", 1, fx.tcx.types.f32),
sym::truncf64 => ("trunc", 1, fx.tcx.types.f64),
sym::rintf32 => ("rintf", 1, fx.tcx.types.f32),
sym::rintf64 => ("rint", 1, fx.tcx.types.f64),
sym::roundf32 => ("roundf", 1, fx.tcx.types.f32),
sym::roundf64 => ("round", 1, fx.tcx.types.f64),
sym::roundevenf32 => ("roundevenf", 1, fx.tcx.types.f32),
sym::roundevenf64 => ("roundeven", 1, fx.tcx.types.f64),
sym::sinf32 => ("sinf", 1, fx.tcx.types.f32),
sym::sinf64 => ("sin", 1, fx.tcx.types.f64),
sym::cosf32 => ("cosf", 1, fx.tcx.types.f32),