0001    //
0002    //  BigUInt Random.swift
0003    //  BigInt
0004    //
0005    //  Created by Károly Lőrentey on 2016-01-04.
0006    //  Copyright © 2016 Károly Lőrentey. All rights reserved.
0007    //
0008    
0009    import Foundation
0010    
0011    extension BigUInt {
0012        //MARK: Random Integers
0013    
0014        /// Create a big integer consisting of `width` uniformly distributed random bits.
0015        ///
0016        /// - Returns: A big integer less than `1 << width`.
0017        /// - Note: This function uses `arc4random_buf` to generate random bits.
0018        @warn_unused_result
0019        public static func randomIntegerWithMaximumWidth
BigUInt Random.swift:43
        var result = randomIntegerWithMaximumWidth(width - 1)
BigUInt Random.swift:55
        var random = randomIntegerWithMaximumWidth(width)
BigUInt Random.swift:57
            random = randomIntegerWithMaximumWidth(width)
(width: Int) -> BigUInt {
0020            guard width > 0 else { return 0 }
0021    
0022            let byteCount = (width + 7) / 8
0023            assert(byteCount > 0)
0024    
0025            let buffer = UnsafeMutablePointer<UInt8>.alloc(byteCount)
0026            defer { buffer.destroy(byteCount) }
0027    
0028            arc4random_buf(buffer, byteCount)
0029            if width % 8 != 0 {
0030                buffer[0] &= UInt8(1 << (width % 8) - 1)
0031            }
0032    
0033            return BigUInt(NSData(bytesNoCopy: buffer, length: byteCount, freeWhenDone: false))
0034        }
0035    
0036        /// Create a big integer consisting of `width-1` uniformly distributed random bits followed by a one bit.
0037        ///
0038        /// - Returns: A random big integer whose width is `width`.
0039        /// - Note: This function uses `arc4random_buf` to generate random bits.
0040        @warn_unused_result
0041        public static func randomIntegerWithExactWidth(width: Int) -> BigUInt {
0042            guard width > 1 else { return BigUInt(width) }
0043            var result = randomIntegerWithMaximumWidth(width - 1)
0044            result[(width - 1) / Digit.width] |= 1 << Digit((width - 1) % Digit.width)
0045            return result
0046        }
0047    
0048        /// Create a uniformly distributed random integer that's less than the specified limit.
0049        ///
0050        /// - Returns: A random big integer that is less than `limit`.
0051        /// - Note: This function uses `arc4random_buf` to generate random bits.
0052        @warn_unused_result
0053        public static func randomIntegerLessThan
BigUInt Prime Test.swift:112
            let random = BigUInt.randomIntegerLessThan(self)
(limit: BigUInt) -> BigUInt {
0054            let width = limit.width
0055            var random = randomIntegerWithMaximumWidth(width)
0056            while random >= limit {
0057                random = randomIntegerWithMaximumWidth(width)
0058            }
0059            return random
0060        }
0061    }
0062