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Reword docs for f32 and f64

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Better explain the reasoning for the `next_up`/`next_down` integer
implementation, as requested by Ralf.
This commit is contained in:
Trevor Gross 2024-06-21 03:30:15 -04:00
parent fce07a82c6
commit 0314fe62bd
2 changed files with 12 additions and 8 deletions
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10
library/core/src/num/f32.rs
View file

@ -796,8 +796,9 @@ pub const fn is_sign_negative(self) -> bool {
#[unstable(feature = "float_next_up_down", issue = "91399")]
#[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
pub const fn next_up(self) -> Self {
// We must use strictly integer arithmetic to prevent denormals from
// flushing to zero after an arithmetic operation on some platforms.
// Some targets violate Rust's assumption of IEEE semantics, e.g. by flushing
// denormals to zero. This is in general unsound and unsupported, but here
// we do our best to still produce the correct result on such targets.
let bits = self.to_bits();
if self.is_nan() || bits == Self::INFINITY.to_bits() {
return self;
@ -843,8 +844,9 @@ pub const fn next_up(self) -> Self {
#[unstable(feature = "float_next_up_down", issue = "91399")]
#[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
pub const fn next_down(self) -> Self {
// We must use strictly integer arithmetic to prevent denormals from
// flushing to zero after an arithmetic operation on some platforms.
// Some targets violate Rust's assumption of IEEE semantics, e.g. by flushing
// denormals to zero. This is in general unsound and unsupported, but here
// we do our best to still produce the correct result on such targets.
let bits = self.to_bits();
if self.is_nan() || bits == Self::NEG_INFINITY.to_bits() {
return self;

10
library/core/src/num/f64.rs
View file

@ -804,8 +804,9 @@ pub fn is_negative(self) -> bool {
#[unstable(feature = "float_next_up_down", issue = "91399")]
#[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
pub const fn next_up(self) -> Self {
// We must use strictly integer arithmetic to prevent denormals from
// flushing to zero after an arithmetic operation on some platforms.
// Some targets violate Rust's assumption of IEEE semantics, e.g. by flushing
// denormals to zero. This is in general unsound and unsupported, but here
// we do our best to still produce the correct result on such targets.
let bits = self.to_bits();
if self.is_nan() || bits == Self::INFINITY.to_bits() {
return self;
@ -851,8 +852,9 @@ pub const fn next_up(self) -> Self {
#[unstable(feature = "float_next_up_down", issue = "91399")]
#[rustc_const_unstable(feature = "float_next_up_down", issue = "91399")]
pub const fn next_down(self) -> Self {
// We must use strictly integer arithmetic to prevent denormals from
// flushing to zero after an arithmetic operation on some platforms.
// Some targets violate Rust's assumption of IEEE semantics, e.g. by flushing
// denormals to zero. This is in general unsound and unsupported, but here
// we do our best to still produce the correct result on such targets.
let bits = self.to_bits();
if self.is_nan() || bits == Self::NEG_INFINITY.to_bits() {
return self;