Struct Invariant 

pub struct Invariant {
    pub value: Option<Value>,
    pub scale: i128,
    pub offset: i128,
}

A value that does not change inside the loop, read as scale * value + offset.

The value is a value defined outside the loop, or None when the expression is a plain number. Keeping the shape rather than a bare Value is what lets j = 2 * i + 3 come out as {3, +, 2} instead of unknown: the base and the step of that chrec are expressions nothing in the function computes, so a representation that could only name existing values would have to give up.

Arithmetic on two of these is refused when both are symbolic and the symbols differ, because x + y is not of this shape. That is the boundary of the subset and it is where the answer becomes unknown rather than wrong.

Fields

value: Option<Value>

What it is built on, or None for a plain number.

scale: i128

How many of it.

offset: i128

What is added to it.

Implementations

impl Invariant

pub fn number(offset: i128) -> Self

A plain number.

pub fn of(value: Value) -> Self

One of a value.

pub fn as_number(self) -> Option<i128>

The number this is, when it is one.

pub fn is_zero(self) -> bool

Whether this is the number zero.

pub fn plus(self, other: Self) -> Option<Self>

The two added, when the sum is of this shape.

pub fn minus(self, other: Self) -> Option<Self>

The second subtracted from the first, when the difference is of this shape.

pub fn negated(self) -> Option<Self>

This with its sign flipped.

pub fn times(self, other: Self) -> Option<Self>

The two multiplied, which needs one of them to be a plain number.

Trait Implementations

impl Clone for Invariant

fn clone(&self) -> Invariant

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Invariant

impl Debug for Invariant

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

Formats the value using the given formatter.

impl Eq for Invariant

impl PartialEq for Invariant

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Invariant