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Rollup merge of #86951 - cyberia-ng:fp-negative-zero-sqrt-docs, r=Mark-Simulacrum

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[docs] Clarify behaviour of f64 and f32::sqrt when argument is negative zero

From IEEE 754 section 6.3:
> Except that squareRoot(−0) shall be −0, every numeric squareRoot result shall have a positive sign.
This commit is contained in:
Yuki Okushi 2021-07-12 04:31:59 +09:00 committed by GitHub
commit 5541d1ac16
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2 changed files with 6 additions and 2 deletions
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4
library/std/src/f32.rs
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@ -324,18 +324,20 @@ impl f32 {
/// Returns the square root of a number.
///
/// Returns NaN if `self` is a negative number.
/// Returns NaN if `self` is a negative number other than `-0.0`.
///
/// # Examples
///
/// ```
/// let positive = 4.0_f32;
/// let negative = -4.0_f32;
/// let negative_zero = -0.0_f32;
///
/// let abs_difference = (positive.sqrt() - 2.0).abs();
///
/// assert!(abs_difference <= f32::EPSILON);
/// assert!(negative.sqrt().is_nan());
/// assert!(negative_zero.sqrt() == negative_zero);
/// ```
#[must_use = "method returns a new number and does not mutate the original value"]
#[stable(feature = "rust1", since = "1.0.0")]

4
library/std/src/f64.rs
View File

@ -324,18 +324,20 @@ impl f64 {
/// Returns the square root of a number.
///
/// Returns NaN if `self` is a negative number.
/// Returns NaN if `self` is a negative number other than `-0.0`.
///
/// # Examples
///
/// ```
/// let positive = 4.0_f64;
/// let negative = -4.0_f64;
/// let negative_zero = -0.0_f64;
///
/// let abs_difference = (positive.sqrt() - 2.0).abs();
///
/// assert!(abs_difference < 1e-10);
/// assert!(negative.sqrt().is_nan());
/// assert!(negative_zero.sqrt() == negative_zero);
/// ```
#[must_use = "method returns a new number and does not mutate the original value"]
#[stable(feature = "rust1", since = "1.0.0")]