Modular arithmetic: Difference between revisions

=={{header|Swift}}==

{{trans|Scala}}

<lang swift>protocol Ring {

associatedtype RingType: Numeric

var one: Self { get }

static func +(_ lhs: Self, _ rhs: Self) -> Self

static func *(_ lhs: Self, _ rhs: Self) -> Self

static func **(_ lhs: Self, _ rhs: Int) -> Self

}

extension Ring {

static func **(_ lhs: Self, _ rhs: Int) -> Self {

var ret = lhs.one

for _ in stride(from: rhs, to: 0, by: -1) {

ret = ret * lhs

}

return ret

}

}

struct ModInt: Ring {

typealias RingType = Int

var value: Int

var modulo: Int

var one: ModInt { ModInt(1, modulo: modulo) }

init(_ value: Int, modulo: Int) {

self.value = value

self.modulo = modulo

}

static func +(lhs: ModInt, rhs: ModInt) -> ModInt {

precondition(lhs.modulo == rhs.modulo)

return ModInt((lhs.value + rhs.value) % lhs.modulo, modulo: lhs.modulo)

}

static func *(lhs: ModInt, rhs: ModInt) -> ModInt {

precondition(lhs.modulo == rhs.modulo)

return ModInt((lhs.value * rhs.value) % lhs.modulo, modulo: lhs.modulo)

}

}

func f<T: Ring>(_ x: T) -> T { (x ** 100) + x + x.one }

let x = ModInt(10, modulo: 13)

let y = f(x)

print("x ^ 100 + x + 1 for x = ModInt(10, 13) is \(y)")</lang>

{{out}}

<pre>x ^ 100 + x + 1 for x = ModInt(10, 13) is ModInt(value: 1, modulo: 13)</pre>