Struct Probability 

pub struct Probability { /* private fields */ }

How likely one edge out of a block is taken, and how much that is worth believing.

Held as parts of Probability::SCALE, which is ten thousand, so a hit rate written as a whole percent is exact and one written to two decimal places is too. GCC’s REG_BR_PROB_BASE is the same idea at the same size.

Implementations

impl Probability

pub const SCALE: u32 = 10_000

What a probability is out of.

pub const fn new(parts: u32, quality: Quality) -> Self

A probability of parts out of Probability::SCALE, believed this much.

There is no constructor that does not say where the number came from, which is section 11.6’s second failure mode closed off at the type. More than the scale is not a probability, and it is clamped rather than refused, because the callers that can produce one are all doing arithmetic where the answer is certainty.

pub const fn percent(percent: u32, quality: Quality) -> Self

A hit rate written as a whole percentage, which is how section 11.2 writes all of them.

pub const fn always() -> Self

The edge is always taken, and that is arithmetic rather than a guess.

pub const fn never() -> Self

The edge is never taken.

pub const fn even() -> Self

Nothing is known about this edge, so it is even and says so.

The starting point for a two way branch no predictor matched. Even and guessed is a different statement from even and measured, and the second one is a real fact about a branch that is genuinely unpredictable.

pub const fn parts(self) -> u32

The parts out of Probability::SCALE.

pub const fn quality(self) -> Quality

How much this is worth believing.

pub const fn complement(self) -> Self

The other edge out of the same branch.

pub fn and(self, other: Self) -> Self

Both, for an edge reached by taking this one and then that one.

The quality is the worse of the two, which is the whole reason these are not bare numbers.

pub fn is_predictable(self) -> bool

Whether a branch this likely one way is one a machine will predict correctly.

Section 40.5, and the part of it that matters is not the threshold. A probability a static predictor guessed never counts as predictable however extreme it is, because the branch predictor in the machine is looking at what the program does and the predictor here is looking at what the program says. Guessing that a loop exit is not taken 89 times in 100 is not evidence about any particular branch.

Trait Implementations

impl Clone for Probability

fn clone(&self) -> Probability

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Probability

impl Debug for Probability

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for Probability

fn fmt(&self, f: &mut Formatter<'_>) -> Result

As a percentage, with the two decimal places only when they say something.

impl Eq for Probability

impl Hash for Probability

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Probability

fn cmp(&self, other: &Probability) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for Probability

fn eq(&self, other: &Probability) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl PartialOrd for Probability

fn partial_cmp(&self, other: &Probability) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl StructuralPartialEq for Probability