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doc: show that f32::log and f64::log are not correctly rounded

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This commit is contained in:
Trevor Spiteri 2018-01-08 19:22:37 +01:00
parent b5392f5450
commit 0eba4c206a
2 changed files with 18 additions and 20 deletions
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19
src/libstd/f32.rs
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@ -470,22 +470,21 @@ impl f32 {
return unsafe { intrinsics::logf32(self) };
}
/// Returns the logarithm of the number with respect to an arbitrary base.
/// Returns the logarithm of the number with respect to an arbitrary base,
/// calculated as `self.ln() / base.ln()`.
///
/// `self.log2()` can produce more accurate results for base 2, and
/// `self.log10()` can produce more accurate results for base 10.
///
/// ```
/// use std::f32;
///
/// let ten = 10.0f32;
/// let two = 2.0f32;
/// let five = 5.0f32;
///
/// // log10(10) - 1 == 0
/// let abs_difference_10 = (ten.log(10.0) - 1.0).abs();
/// // log5(5) - 1 == 0
/// let abs_difference = (five.log(5.0) - 1.0).abs();
///
/// // log2(2) - 1 == 0
/// let abs_difference_2 = (two.log(2.0) - 1.0).abs();
///
/// assert!(abs_difference_10 <= f32::EPSILON);
/// assert!(abs_difference_2 <= f32::EPSILON);
/// assert!(abs_difference <= f32::EPSILON);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]

19
src/libstd/f64.rs
View file

@ -430,20 +430,19 @@ impl f64 {
self.log_wrapper(|n| { unsafe { intrinsics::logf64(n) } })
}
/// Returns the logarithm of the number with respect to an arbitrary base.
/// Returns the logarithm of the number with respect to an arbitrary base,
/// calculated as `self.ln() / base.ln()`.
///
/// `self.log2()` can produce more accurate results for base 2, and
/// `self.log10()` can produce more accurate results for base 10.
///
/// ```
/// let ten = 10.0_f64;
/// let two = 2.0_f64;
/// let five = 5.0_f64;
///
/// // log10(10) - 1 == 0
/// let abs_difference_10 = (ten.log(10.0) - 1.0).abs();
/// // log5(5) - 1 == 0
/// let abs_difference = (five.log(5.0) - 1.0).abs();
///
/// // log2(2) - 1 == 0
/// let abs_difference_2 = (two.log(2.0) - 1.0).abs();
///
/// assert!(abs_difference_10 < 1e-10);
/// assert!(abs_difference_2 < 1e-10);
/// assert!(abs_difference < 1e-10);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]