mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Rollup merge of #125253 - sunsided:feature/FRAC_1_SQRT_PI, r=Mark-Simulacrum

Browse Source 
Add `FRAC_1_SQRT_2PI` constant to f16/f32/f64/f128

This adds the `FRAC_1_SQRT_2PI` to the `f16`, `f32`, `f64` and `f128` as [`1/√(2π)`](https://www.wolframalpha.com/input?i=1%2Fsqrt%282*pi%29). The rationale is that while `FRAC_1_SQRT_PI` already exists, [Gaussian calculations](https://en.wikipedia.org/wiki/Gaussian_function) for random normal distributions require a `1/(σ√(2π))` term, which could then be directly expressed e.g. as `f32::FRAC_1_SQRT_2PI / sigma`.

The actual value is approximately `1/√(2π) = 0.3989422804014326779399460599343818684758586311649346576659258296…`. Truncated/rounded forms were used for the individual types.

---

~~I did not any of the `#[unstable]` attributes since I am not aware of their implications.~~

**Edit:** I applied the stability attributes from the surrounding types according to what seemed most likely correct. I believe the `more_float_constants` feature marker is incorrectly applied, but I wasn't sure how to proceed.
This commit is contained in:
许杰友 Jieyou Xu (Joe) 2024-06-09 19:16:19 +01:00 committed by GitHub
commit 61671a7e34
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
4 changed files with 23 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
library/core/src/num/f128.rs
View File

@ -68,6 +68,13 @@ pub mod consts {
pub const FRAC_1_SQRT_PI: f128 =
0.564189583547756286948079451560772585844050629328998856844086_f128;
/// 1/sqrt(2π)
#[doc(alias = "FRAC_1_SQRT_TAU")]
#[unstable(feature = "f128", issue = "116909")]
// Also, #[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_2PI: f128 =
0.398942280401432677939946059934381868475858631164934657665926_f128;
/// 2/π
#[unstable(feature = "f128", issue = "116909")]
pub const FRAC_2_PI: f128 = 0.636619772367581343075535053490057448137838582961825794990669_f128;

6
library/core/src/num/f16.rs
View File

@ -67,6 +67,12 @@ pub mod consts {
// Also, #[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_PI: f16 = 0.564189583547756286948079451560772586_f16;
/// 1/sqrt(2π)
#[doc(alias = "FRAC_1_SQRT_TAU")]
#[unstable(feature = "f16", issue = "116909")]
// Also, #[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_2PI: f16 = 0.398942280401432677939946059934381868_f16;
/// 2/π
#[unstable(feature = "f16", issue = "116909")]
pub const FRAC_2_PI: f16 = 0.636619772367581343075535053490057448_f16;

5
library/core/src/num/f32.rs
View File

@ -327,6 +327,11 @@ pub mod consts {
#[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_PI: f32 = 0.564189583547756286948079451560772586_f32;
/// 1/sqrt(2π)
#[doc(alias = "FRAC_1_SQRT_TAU")]
#[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_2PI: f32 = 0.398942280401432677939946059934381868_f32;
/// 2/π
#[stable(feature = "rust1", since = "1.0.0")]
pub const FRAC_2_PI: f32 = 0.636619772367581343075535053490057448_f32;

5
library/core/src/num/f64.rs
View File

@ -327,6 +327,11 @@ pub mod consts {
#[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_PI: f64 = 0.564189583547756286948079451560772586_f64;
/// 1/sqrt(2π)
#[doc(alias = "FRAC_1_SQRT_TAU")]
#[unstable(feature = "more_float_constants", issue = "103883")]
pub const FRAC_1_SQRT_2PI: f64 = 0.398942280401432677939946059934381868_f64;
/// 2/π
#[stable(feature = "rust1", since = "1.0.0")]
pub const FRAC_2_PI: f64 = 0.636619772367581343075535053490057448_f64;