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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Collections open source project
//
// Copyright (c) 2023 - 2024 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//
/// A commutative group that is used to augment a tree, enabling quick lookup operations.
public protocol RopeSummary: Equatable, Sendable {
static var maxNodeSize: Int { get }
static var nodeSizeBitWidth: Int { get }
/// The identity element of the group.
static var zero: Self { get }
/// Returns a Boolean value that indicates whether `self` is the identity element.
var isZero: Bool { get }
/// A commutative and associative operation that combines two instances.
///
/// (As is usually the case, this operation is not necessarily closed over `Self` in practice --
/// e.g., some results may not be representable.)
mutating func add(_ other: Self)
/// A (potentially partial) subtraction function that undoes a previous combination of the given
/// element to `self`.
///
/// The inverse of any instance can be calculated by subtracting it from the `zero` instance.
/// (However, conforming types are free to require that `subtract` only be called on values
/// that "include" the given `other`.)
mutating func subtract(_ other: Self)
}
extension RopeSummary {
@inlinable @inline(__always)
public static var nodeSizeBitWidth: Int {
Int.bitWidth - maxNodeSize.leadingZeroBitCount
}
@inlinable @inline(__always)
public static var minNodeSize: Int { (maxNodeSize + 1) / 2 }
}
extension RopeSummary {
@inlinable
public func adding(_ other: Self) -> Self {
var c = self
c.add(other)
return c
}
@inlinable
public func subtracting(_ other: Self) -> Self {
var c = self
c.subtract(other)
return c
}
}
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