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Document rounding for floating-point primitive operations

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State that the four primitive operations honour IEEE 754 roundTiesToEven.

Documenting under "Primitive Type f32"; f64 refers to that.
This commit is contained in:
Matthew Woodcraft 2022-04-16 21:58:36 +01:00
parent 2fa9789f59
commit 6fa061c5f9
2 changed files with 26 additions and 0 deletions
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13
library/core/src/primitive_docs.rs
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@ -982,6 +982,19 @@ mod prim_tuple {}
/// it is considered infectious as almost all calculations where one of the
/// operands is NaN will also result in NaN.
///
/// When the number resulting from a primitive operation (addition,
/// subtraction, multiplication, or division) on this type is not exactly
/// representable as `f32`, it is rounded according to the roundTiesToEven
/// direction defined in IEEE 754-2008. That means:
///
/// - The result is the representable value closest to the true value, if there
/// is a unique closest representable value.
/// - If the true value is exactly half-way between two representable values,
/// the result is the one with an even least-significant binary digit.
/// - If the true value's magnitude is ≥ `f32::MAX` + 2<sup>(`f32::MAX_EXP` −
/// `f32::MANTISSA_DIGITS` − 1)</sup>, the result is ∞ or −∞ (preserving the
/// true value's sign).
///
/// For more information on floating point numbers, see [Wikipedia][wikipedia].
///
/// *[See also the `std::f32::consts` module](crate::f32::consts).*

13
library/std/src/primitive_docs.rs
View File

@ -982,6 +982,19 @@ mod prim_tuple {}
/// it is considered infectious as almost all calculations where one of the
/// operands is NaN will also result in NaN.
///
/// When the number resulting from a primitive operation (addition,
/// subtraction, multiplication, or division) on this type is not exactly
/// representable as `f32`, it is rounded according to the roundTiesToEven
/// direction defined in IEEE 754-2008. That means:
///
/// - The result is the representable value closest to the true value, if there
/// is a unique closest representable value.
/// - If the true value is exactly half-way between two representable values,
/// the result is the one with an even least-significant binary digit.
/// - If the true value's magnitude is ≥ `f32::MAX` + 2<sup>(`f32::MAX_EXP` −
/// `f32::MANTISSA_DIGITS` − 1)</sup>, the result is ∞ or −∞ (preserving the
/// true value's sign).
///
/// For more information on floating point numbers, see [Wikipedia][wikipedia].
///
/// *[See also the `std::f32::consts` module](crate::f32::consts).*