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+//
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+// BigNum.swift
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+// Swifter
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+//
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+// Created by Damian Kolakowski on 08/08/16.
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+//
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+
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+import Foundation
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+
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+public struct BigNum {
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+
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+ //
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+ // Big Integer
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+ //
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+ // TODO/Improvments
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+ // - add init(...) for string literal
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+ // - switch to 'long division'
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+ // - fix '+' and '-' operators for negative numbers
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+
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+ internal var digits = [UInt8]()
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+ internal var signum = 0
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+
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+ internal init(_ digits: [UInt8]) {
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+ self.digits.append(contentsOf: digits)
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+ self.signum = digits.isEmpty ? 0 : 1
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+ }
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+
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+ public init(_ text: String) {
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+ self.signum = text.unicodeScalars.isEmpty ? 0 : 1
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+ for c in text.unicodeScalars.reversed() {
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+ switch c.value {
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+ case 48...57:
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+ self.digits.append(UInt8(c.value-48))
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+ case 45:
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+ self.signum = -1
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+ default: break
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+ }
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+ }
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+ }
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+}
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+
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+infix operator == { }
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+public func == (_ left: BigNum, right: BigNum) -> Bool {
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+ return (left.digits == right.digits) && (left.signum == right.signum)
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+}
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+
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+infix operator + { }
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+public func + (_ left: BigNum, _ right: BigNum) -> BigNum {
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+ var result = [UInt8]()
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+ var carry: UInt8 = 0
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+ for i in 0..<max(left.digits.count, right.digits.count) {
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+ let leftDigit = (i < left.digits.count) ? left.digits[i] : 0
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+ let rightDigit = (i < right.digits.count) ? right.digits[i] : 0
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+ let sum = (leftDigit + rightDigit) + carry
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+ if sum > 9 {
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+ carry = 1
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+ result.append(sum - 10)
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+ } else {
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+ carry = 0
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+ result.append(sum)
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+ }
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+ }
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+ if carry != 0 {
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+ result.append(carry)
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+ }
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+ return BigNum(result)
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+}
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+
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+infix operator - { }
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+public func - (_ left: BigNum, _ right: BigNum) -> BigNum {
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+ var result = [UInt8]()
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+ var carry: Int = 0
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+ for i in 0..<max(left.digits.count, right.digits.count) {
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+ let leftDigit = (i < left.digits.count) ? left.digits[i] : 0
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+ let rightDigit = (i < right.digits.count) ? right.digits[i] : 0
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+ let diff = (Int(leftDigit) - Int(rightDigit)) + carry
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+ if diff < 0 {
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+ carry = -1
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+ result.append(UInt8(10+diff))
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+ } else {
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+ carry = 0
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+ result.append(UInt8(diff))
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+ }
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+ }
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+ while let last = result.last, last == 0 { result.removeLast() }
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+ return BigNum(result)
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+}
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+
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+infix operator * { }
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+public func * (_ left: BigNum, _ right: BigNum) -> BigNum {
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+ var mulResults = Array<[UInt8]>()
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+ for i in 0..<left.digits.count {
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+ var row = [UInt8](repeating: 0, count: i)
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+ var carry: UInt8 = 0
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+ for j in 0..<right.digits.count {
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+ let mul = (left.digits[i] * right.digits[j]) + carry
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+ if mul > 9 {
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+ carry = mul / 10
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+ row.append(mul % 10)
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+ } else {
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+ carry = 0
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+ row.append(mul)
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+ }
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+ }
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+ if carry != 0 {
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+ row.append(carry % 10)
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+ if carry > 9 { row.append(carry / 10) }
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+ }
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+ mulResults.append(row)
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+ }
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+ var sum = mulResults.reduce(BigNum([0])) { $0.partialResult + BigNum($0.1) }
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+ sum.signum = left.signum * right.signum
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+ return sum
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+}
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+
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+infix operator / { }
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+public func / (_ left: BigNum, _ right: BigNum) -> BigNum {
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+ if left < right {
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+ return BigNum([0])
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+ }
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+ var quotient = BigNum([0])
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+ var remainder = left
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+
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+ while remainder >= right {
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+ quotient = quotient + BigNum([1])
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+ remainder = remainder - right
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+ }
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+
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+ quotient.signum = left.signum * right.signum
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+
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+ return quotient
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+}
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+
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+infix operator % { }
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+public func % (_ left: BigNum, _ right: BigNum) -> BigNum {
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+ if left < right {
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+ return left
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+ }
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+ var quotient = BigNum([0])
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+ var remainder = left
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+
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+ while remainder >= right {
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+ quotient = quotient + BigNum([1])
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+ remainder = remainder - right
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+ }
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+ return remainder
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+}
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+
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+infix operator > { }
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+public func > (_ left: BigNum, _ right: BigNum) -> Bool {
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+ if left.signum != right.signum {
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+ return left.signum > right.signum
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+ }
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+ if left.digits.count != right.digits.count {
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+ if left.signum < 0 {
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+ return left.digits.count < right.digits.count
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+ } else {
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+ return left.digits.count > right.digits.count
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+ }
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+ }
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+ for i in 0..<left.digits.count {
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+ if left.digits[i] == right.digits[i] {
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+ continue
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+ }
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+ if left.signum < 0 {
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+ if left.digits[i] < right.digits[i] {
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+ return true
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+ }
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+ } else {
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+ if left.digits[i] > right.digits[i] {
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+ return true
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+ }
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+ }
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+ }
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+ return false
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+}
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+
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+infix operator < { }
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+public func < (_ left: BigNum, _ right: BigNum) -> Bool {
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+ if left.signum != right.signum {
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+ return left.signum < right.signum
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+ }
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+ if right.digits.count != left.digits.count {
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+ if left.signum < 0 {
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+ return left.digits.count > right.digits.count
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+ } else {
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+ return left.digits.count < right.digits.count
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+ }
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+ }
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+ for i in 0..<left.digits.count {
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+ if left.digits[i] == right.digits[i] {
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+ continue
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+ }
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+ if left.signum < 0 {
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+ if right.digits[i] < left.digits[i] {
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+ return true
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+ }
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+ } else {
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+ if right.digits[i] > left.digits[i] {
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+ return true
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+ }
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+ }
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+ }
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+ return false
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+}
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+
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+infix operator >= { }
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+public func >= (_ left: BigNum, _ right: BigNum) -> Bool {
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+ return (left == right) || (left > right)
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+}
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+
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+infix operator <= { }
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+public func <= (_ left: BigNum, _ right: BigNum) -> Bool {
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+ return (left == right) || (left < right)
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+}
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Damian Kołakowski