Enum shakmaty_syzygy::MaybeRounded

pub enum MaybeRounded<T> {
    Rounded(T),
    Precise(T),
}

A value that may be affected by DTZ rounding.

DTZ

Rounded Dtz values may be off by one:

• MaybeRounded::Rounded(Dtz(-n)) can mean a loss with a forced zeroing move in n or n + 1 plies.
• MaybeRounded::Rounded(Dtz(n)) can mean a win with a forced zeroing move in n or n + 1 plies.

WDL

Because of that MaybeRounded::Rounded(Dtz(100)) might correspond to Wdl::Win or Wdl::CursedWin, and MaybeRounded::Rounded(Dtz(-100)) might correspond to Wdl::Loss or Wdl::BlessedLoss.

Rounding will never be used for endgame phases that are exactly on the edge of the 50-move rule (value ±100 directly after a capture or pawn move).

Move selection

So some primary tablebase lines may waste up to 1 ply, but never more, and never for endgame phases (starting after a capture or pawn move) where wasting 1 ply would change the game theoretical outcome.

Users need to be careful in positions that are nearly drawn under the 50-move rule! Carelessly wasting 1 more ply by not following the tablebase recommendation, for a total of 2 wasted plies, may change the outcome of the game afterall.

For some background, see this and the following posts on talkchess.com.

Variants

Rounded(T)

Inner value potentially affected by DTZ rounding.

Precise(T)

Inner value not affected by DTZ rounding.

Implementations

impl<T> MaybeRounded<T>

pub fn map<U, F>(self, f: F) -> MaybeRounded<U>where
    F: FnOnce(T) -> U,

Applies a function to the inner value.

pub fn ignore_rounding(self) -> T

Gets the inner value.

pub fn precise(self) -> Option<T>

Gets the inner value, or None if it was affected by DTZ rounding.

impl MaybeRounded<Dtz>

pub fn is_zero(self) -> bool

See Dtz::is_zero().

pub fn is_positive(self) -> bool

See Dtz::is_positive().

pub fn is_negative(self) -> bool

See Dtz::is_negative().

pub fn signum(self) -> i32

See Dtz::signum().

pub fn add_plies(self, plies: u32) -> MaybeRounded<Dtz>

See Dtz::add_plies().

pub fn add_plies_checked(self, plies: u32) -> MaybeRounded<Option<Dtz>>

See Dtz::add_plies_checked().

pub fn add_plies_saturating(self, plies: u32) -> MaybeRounded<Dtz>

See Dtz::add_plies_saturating().

Trait Implementations

impl<T: Clone> Clone for MaybeRounded<T>

fn clone(&self) -> MaybeRounded<T>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T: Debug> Debug for MaybeRounded<T>

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

Formats the value using the given formatter.

impl<T: Neg> Neg for MaybeRounded<T>

type Output = MaybeRounded<<T as Neg>::Output>

The resulting type after applying the - operator.

fn neg(self) -> Self::Output

Performs the unary - operation.

impl<T: Copy> Copy for MaybeRounded<T>