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Add a copysign function to f32 and f64 #55169

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merged 3 commits into from
Oct 19, 2018
Merged

Add a copysign function to f32 and f64 #55169

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0e6c3f2
Add a `copysign` function to f32 and f64
raphlinus Oct 18, 2018
9a2e702
Fix inconsistent documentation
raphlinus Oct 18, 2018
f08db6b
Add must_use on copysign
raphlinus Oct 18, 2018
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29 changes: 29 additions & 0 deletions src/libstd/f32.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -198,6 +198,35 @@ impl f32 {
}
}

/// Returns a number composed of the magnitude of one number and the sign of
/// another.
///
/// Equal to `self` if the sign of `self` and `y` are the same, otherwise
/// equal to `-y`. If `self` is a `NAN`, then a `NAN` with the sign of `y`
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"otherwise equal to -self", and not "-y", right? Or am I confused now?

Also: I'd rephrase the first sentence to "Returns a number composed of the magnitude of self and the sign of y". That's more explicit.

And yes, I know the PR is already merged, but I guess we should fix this in a new PR, if I'm right about this typo.

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@LukasKalbertodt You're absolutely right. I'm happy to fix this in a followup PR. Good catch!

/// is returned.
///
/// # Examples
///
/// ```
/// #![feature(copysign)]
/// use std::f32;
///
/// let f = 3.5_f32;
///
/// assert_eq!(f.copysign(0.42), 3.5_f32);
/// assert_eq!(f.copysign(-0.42), -3.5_f32);
/// assert_eq!((-f).copysign(0.42), 3.5_f32);
/// assert_eq!((-f).copysign(-0.42), -3.5_f32);
///
/// assert!(f32::NAN.copysign(1.0).is_nan());
/// ```
#[inline]
#[must_use]
#[unstable(feature="copysign", issue="55169")]
pub fn copysign(self, y: f32) -> f32 {
unsafe { intrinsics::copysignf32(self, y) }
}

/// Fused multiply-add. Computes `(self * a) + b` with only one rounding
/// error, yielding a more accurate result than an unfused multiply-add.
///
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29 changes: 29 additions & 0 deletions src/libstd/f64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -176,6 +176,35 @@ impl f64 {
}
}

/// Returns a number composed of the magnitude of one number and the sign of
/// another.
///
/// Equal to `self` if the sign of `self` and `y` are the same, otherwise
/// equal to `-y`. If `self` is a `NAN`, then a `NAN` with the sign of `y`
/// is returned.
///
/// # Examples
///
/// ```
/// #![feature(copysign)]
/// use std::f64;
///
/// let f = 3.5_f64;
///
/// assert_eq!(f.copysign(0.42), 3.5_f64);
/// assert_eq!(f.copysign(-0.42), -3.5_f64);
/// assert_eq!((-f).copysign(0.42), 3.5_f64);
/// assert_eq!((-f).copysign(-0.42), -3.5_f64);
///
/// assert!(f64::NAN.copysign(1.0).is_nan());
/// ```
#[inline]
#[must_use]
#[unstable(feature="copysign", issue="55169")]
pub fn copysign(self, y: f64) -> f64 {
unsafe { intrinsics::copysignf64(self, y) }
}

/// Fused multiply-add. Computes `(self * a) + b` with only one rounding
/// error, yielding a more accurate result than an unfused multiply-add.
///
Expand Down