Tracking Issue (take 2) for `more_float_constants`

Feature gate: #![feature(more_float_constants)]

This is a tracking issue for additional constants in the {f16, f32, f64, f128}::consts modules. Most of these match C++, with the exception of 1/sqrt(2π) https://en.cppreference.com/w/cpp/numeric/constants.html.

The original tracking issue was https://github.com/rust-lang/rust/issues/103883 but we lost the ability to edit the top post.

Public API

// in core::{f16, f32, f64, f128}::consts

/// 1/sqrt(π)
pub const FRAC_1_SQRT_PI: f64 = 0.564189583547756286948079451560772586_f64;

/// 1/sqrt(2π)
pub const FRAC_1_SQRT_2PI: f64 = 0.398942280401432677939946059934381868_f64;

/// sqrt(3)
pub const SQRT_3: f64 = 1.732050807568877293527446341505872367_f64;

/// 1/sqrt(3)
pub const FRAC_1_SQRT_3: f64 = 0.577350269189625764509148780501957456_f64;

/* Already stabilized as euler_gamma_golden_ratio */

/// The golden ratio (φ)
pub const GOLDEN_RATIO: f64 = 1.618033988749894848204586834365638118_f64;

/// The Euler-Mascheroni constant (γ)
pub const EULER_GAMMA: f64 = 0.577215664901532860606512090082402431_f64;

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• ACP: https://github.com/rust-lang/libs-team/issues/119
• ACP for FRAC_1_SQRT_2PI https://github.com/rust-lang/libs-team/issues/383
• Implementation: https://github.com/rust-lang/rust/pull/103836
• Add FRAC_1_SQRT_2PI https://github.com/rust-lang/rust/pull/125253
• Add constants for f16 and f128 https://github.com/rust-lang/rust/pull/123850
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• Naming of the Euler-Mascheroni constant (gamma).
• FRAC_1_SQRT_2PI or FRAC_1_SQRT_TAU to match the existing TAU
• Any additional constants?
  • ln(3)
  • SQRT_5 https://github.com/rust-lang/rust/issues/103883#issuecomment-1563429653
  • FRAC_1_SQRT_5 https://github.com/rust-lang/rust/issues/103883#issuecomment-3324411919
• How do we decide whether or not a constant makes the cutoff?

Start with the core::{f16, f32, f64, f128}::consts API and the linked implementation and constant-addition pull requests. Review the unresolved questions about naming, additional constants, and the cutoff, then follow the stabilization process; done requires completing the final comment period and stabilization PR.