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Rollup merge of #106798 - scottmcm:signum-via-cmp, r=Mark-Simulacrum

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Implement `signum` with `Ord`

Rather than needing to do things like #105840 for `signum` too, might as well just implement that method using `Ord`, since it's doing the same "I need `-1`/`0`/`+1`" behaviour that `cmp` is already doing.

This also seems to slightly improve the assembly: <https://rust.godbolt.org/z/5oEEqbxK1>
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Matthias Krüger 2023-01-29 20:03:36 +01:00 committed by GitHub
commit 782da867c8
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1 changed files with 6 additions and 5 deletions
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library/core/src/num/int_macros.rs
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@ -2574,12 +2574,13 @@ macro_rules! int_impl {
#[must_use = "this returns the result of the operation, \ #[must_use = "this returns the result of the operation, \
without modifying the original"] without modifying the original"]
#[inline(always)] #[inline(always)]
#[rustc_allow_const_fn_unstable(const_cmp)]
pub const fn signum(self) -> Self { pub const fn signum(self) -> Self {
match self { // Picking the right way to phrase this is complicated
n if n > 0 => 1, // (<https://graphics.stanford.edu/~seander/bithacks.html#CopyIntegerSign>)
0 => 0, // so delegate it to `Ord` which is already producing -1/0/+1
_ => -1, // exactly like we need and can be the place to deal with the complexity.
} self.cmp(&0) as _
} }
/// Returns `true` if `self` is positive and `false` if the number is zero or /// Returns `true` if `self` is positive and `false` if the number is zero or