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Optimise floating point is_finite (2x) and is_infinite (1.6x). #57353

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Jan 13, 2019
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Optimise floating point is_finite (2x) and is_infinite (1.6x). #57353

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14 changes: 12 additions & 2 deletions src/libcore/num/f32.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -161,6 +161,14 @@ impl f32 {
self != self
}

// FIXME(#50145): `abs` is publicly unavailable in libcore due to
// concerns about portability, so this implementation is for
// private use internally.
#[inline]
fn abs_private(self) -> f32 {
f32::from_bits(self.to_bits() & 0x7fff_ffff)
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Why is this necessary, rather than using the existing abs method (which uses the LLVM fabsf32 intrinsic directly)?

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That's only available in std. #50145

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@varkor varkor Jan 5, 2019 •
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I'm bikeshedding here, but given typical naming conventions, I think it'd make sense to simply call this abs (which shouldn't cause any conflicts) and add a comment explaining why this method is private for discoverability, e.g.

// FIXME(#50145): `abs` is publicly unavailable in libcore due to concerns
// about portability, so this implementation is for private use internally.

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I agree about adding a comment, but I don't think that naming it abs is appropriate. I'd call it something like abs_hack so it's clear that it's not using the proper abs method.

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How about abs_private with a comment?

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Added that.

}

/// Returns `true` if this value is positive infinity or negative infinity and
/// false otherwise.
///
Expand All @@ -181,7 +189,7 @@ impl f32 {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is_infinite(self) -> bool {
self == INFINITY || self == NEG_INFINITY
self.abs_private() == INFINITY
}

/// Returns `true` if this number is neither infinite nor `NaN`.
Expand All @@ -203,7 +211,9 @@ impl f32 {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is_finite(self) -> bool {
!(self.is_nan() || self.is_infinite())
// There's no need to handle NaN separately: if self is NaN,
// the comparison is not true, exactly as desired.
self.abs_private() < INFINITY
}

/// Returns `true` if the number is neither zero, infinite,
Expand Down
14 changes: 12 additions & 2 deletions src/libcore/num/f64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -161,6 +161,14 @@ impl f64 {
self != self
}

// FIXME(#50145): `abs` is publicly unavailable in libcore due to
// concerns about portability, so this implementation is for
// private use internally.
#[inline]
fn abs_private(self) -> f64 {
f64::from_bits(self.to_bits() & 0x7fff_ffff_ffff_ffff)
}

/// Returns `true` if this value is positive infinity or negative infinity and
/// false otherwise.
///
Expand All @@ -181,7 +189,7 @@ impl f64 {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is_infinite(self) -> bool {
self == INFINITY || self == NEG_INFINITY
self.abs_private() == INFINITY
}

/// Returns `true` if this number is neither infinite nor `NaN`.
Expand All @@ -203,7 +211,9 @@ impl f64 {
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn is_finite(self) -> bool {
!(self.is_nan() || self.is_infinite())
// There's no need to handle NaN separately: if self is NaN,
// the comparison is not true, exactly as desired.
self.abs_private() < INFINITY
}

/// Returns `true` if the number is neither zero, infinite,
Expand Down