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Document round-off error in .mod_euc()-method, see issue #50179

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This commit is contained in:
Fabian Kössel 2018-04-30 16:06:53 +02:00
parent 773ce53ce7
commit af6f0f2e10
2 changed files with 12 additions and 2 deletions
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7
src/libstd/f32.rs
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@ -254,7 +254,10 @@ impl f32 {
/// Calculates the Euclidean modulo (self mod rhs), which is never negative.
///
/// In particular, the result `n` satisfies `0 <= n < rhs.abs()`.
/// In particular, the return value `r` satisfies `0.0 <= r < rhs.abs()` in
/// most cases. However, due to a floating point round-off error it can
/// result in `r == rhs.abs()`, violating the mathematical definition, if
/// `self` is much smaller than `rhs.abs()` in magnitude and `self < 0.0`.
///
/// # Examples
///
@ -266,6 +269,8 @@ impl f32 {
/// assert_eq!((-a).mod_euc(b), 1.0);
/// assert_eq!(a.mod_euc(-b), 3.0);
/// assert_eq!((-a).mod_euc(-b), 1.0);
/// // limitation due to round-off error
/// assert!((-std::f32::EPSILON).mod_euc(3.0) != 0.0);
/// ```
#[inline]
#[unstable(feature = "euclidean_division", issue = "49048")]

7
src/libstd/f64.rs
View File

@ -230,7 +230,10 @@ impl f64 {
/// Calculates the Euclidean modulo (self mod rhs), which is never negative.
///
/// In particular, the result `n` satisfies `0 <= n < rhs.abs()`.
/// In particular, the return value `r` satisfies `0.0 <= r < rhs.abs()` in
/// most cases. However, due to a floating point round-off error it can
/// result in `r == rhs.abs()`, violating the mathematical definition, if
/// `self` is much smaller than `rhs.abs()` in magnitude and `self < 0.0`.
///
/// # Examples
///
@ -242,6 +245,8 @@ impl f64 {
/// assert_eq!((-a).mod_euc(b), 1.0);
/// assert_eq!(a.mod_euc(-b), 3.0);
/// assert_eq!((-a).mod_euc(-b), 1.0);
/// // limitation due to round-off error
/// assert!((-std::f64::EPSILON).mod_euc(3.0) != 0.0);
/// ```
#[inline]
#[unstable(feature = "euclidean_division", issue = "49048")]