Tracking Issue for `float_mul_add_relaxed`

Feature gate: #![feature(float_mul_add_relaxed)]

This is a tracking issue for the mul_add_relaxed method on floating-point types which is either mul_add (1 rounding) or *+ (2 roundings), nondeterministically.

Public API

// in std
impl f32/f64/... {
    pub fn mul_add_relaxed(self, multiplicand: Self, addend: Self) -> Self;
}

Steps / History

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

• ACP: https://github.com/rust-lang/libs-team/issues/712
• Implementation:
  • https://github.com/rust-lang/rust/pull/124874
  • #151793
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• We would like to see some documentation added to the effect of "If you want some target-specific performance optimization possibilities but need a guarantee of either the fused or unfused behavior, use this. If you want even more performance and aren't concerned about error bounds, use the algebraic_* functions such as algebraic_mul and algebraic_add.".

Start with the implementation links in the Steps / History section, especially rust-lang/rust#124874 and issue #151793, then review the public API and unresolved documentation requirement. Done means the implementation, final comment period, stabilization PR, and requested guidance on fused versus unfused behavior are complete.