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deprecate f{32,64}::DIGITS #89238

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deprecate f{32,64}::DIGITS #89238

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25 changes: 19 additions & 6 deletions library/core/src/num/f32.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,21 +54,28 @@ pub const RADIX: u32 = f32::RADIX;
)]
pub const MANTISSA_DIGITS: u32 = f32::MANTISSA_DIGITS;

/// Approximate number of significant digits in base 10.
/// Use [`f32::DIGITS`] instead.
/// A minimum number of significant digits in base 10.
/// This value is likely incorrect for usage,
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just need to elaborate on this and add a small example of how this can be incorrect.

/// as it is not the upper limit of significant digits `f32` can contain.
///
/// # Examples
///
/// ```rust
/// // deprecated way
/// # #[allow(deprecated, deprecated_in_future)]
/// let d = std::f32::DIGITS;
///
/// // intended way
/// // also deprecated
/// # #[allow(deprecated, deprecated_in_future)]
/// let d = f32::DIGITS;
///
/// // the intended way may vary by application
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_deprecated(since = "TBD", reason = "replaced by the `DIGITS` associated constant on `f32`")]
#[rustc_deprecated(
since = "TBD",
reason = "this value is incorrect or misleading as it actually encompasses a range"
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Really tiny nit, but I feel like the word 'encompasses' is misleading here. I might read that and think that the deprecated value is the upper bound, and therefore safe.
Maybe change it to say "the actual number of significant digits varies over a range, and this value is the minimum number of significant digits" or something else that makes the problem clear.

)]
#[allow(deprecated, deprecated_in_future)]
pub const DIGITS: u32 = f32::DIGITS;

/// [Machine epsilon] value for `f32`.
Expand Down Expand Up @@ -381,8 +388,14 @@ impl f32 {
#[stable(feature = "assoc_int_consts", since = "1.43.0")]
pub const MANTISSA_DIGITS: u32 = 24;

/// Approximate number of significant digits in base 10.
/// A minimum number of significant digits in base 10.
/// This value is likely incorrect for usage,
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and here as well

/// as it is not the upper limit of significant digits `f32` can contain.
#[stable(feature = "assoc_int_consts", since = "1.43.0")]
#[rustc_deprecated(
since = "TBD",
reason = "this value is incorrect or misleading as it actually encompasses a range"
)]
pub const DIGITS: u32 = 6;

/// [Machine epsilon] value for `f32`.
Expand Down
26 changes: 20 additions & 6 deletions library/core/src/num/f64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,21 +54,28 @@ pub const RADIX: u32 = f64::RADIX;
)]
pub const MANTISSA_DIGITS: u32 = f64::MANTISSA_DIGITS;

/// Approximate number of significant digits in base 10.
/// Use [`f64::DIGITS`] instead.
/// A minimum number of significant digits in base 10.
/// This value is likely incorrect for usage,
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here too

/// as it is not the upper limit of significant digits `f64` can contain.
///
/// # Examples
///
/// ```rust
/// // deprecated way
/// # #[allow(deprecated, deprecated_in_future)]
/// let d = std::f64::DIGITS;
///
/// // intended way
/// // also deprecated
/// # #[allow(deprecated, deprecated_in_future)]
/// let d = f64::DIGITS;
///
/// // the intended way may vary by application
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_deprecated(since = "TBD", reason = "replaced by the `DIGITS` associated constant on `f64`")]
#[rustc_deprecated(
since = "TBD",
reason = "this value is incorrect or misleading as it actually encompasses a range"
)]
#[allow(deprecated, deprecated_in_future)]
pub const DIGITS: u32 = f64::DIGITS;

/// [Machine epsilon] value for `f64`.
Expand Down Expand Up @@ -380,8 +387,15 @@ impl f64 {
/// Number of significant digits in base 2.
#[stable(feature = "assoc_int_consts", since = "1.43.0")]
pub const MANTISSA_DIGITS: u32 = 53;
/// Approximate number of significant digits in base 10.

/// A minimum number of significant digits in base 10.
/// This value is likely incorrect for usage,
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and here

/// as it is not the upper limit of significant digits `f64` can contain.
#[stable(feature = "assoc_int_consts", since = "1.43.0")]
#[rustc_deprecated(
since = "TBD",
reason = "this value is incorrect or misleading as it actually encompasses a range"
)]
pub const DIGITS: u32 = 15;

/// [Machine epsilon] value for `f64`.
Expand Down