CryptoSwift/Sources/CryptoSwift/Collection+Extension.swift

//
//  Collection+Extension.swift
//  CryptoSwift
//
//  Created by Marcin Krzyzanowski on 02/08/16.
//  Copyright © 2016 Marcin Krzyzanowski. All rights reserved.
//

extension Collection where Self.Iterator.Element == UInt8, Self.Index == Int {
    func toUInt32Array() -> Array<UInt32> {
        var result = Array<UInt32>()
        result.reserveCapacity(16)
        for idx in stride(from: self.startIndex, to: self.endIndex, by: MemoryLayout<UInt32>.size) {
            var val: UInt32 = 0
            val |= self.count > 3 ? UInt32(self[idx.advanced(by: 3)]) << 24 : 0
            val |= self.count > 2 ? UInt32(self[idx.advanced(by: 2)]) << 16 : 0
            val |= self.count > 1 ? UInt32(self[idx.advanced(by: 1)]) << 8  : 0
            val |= self.count > 0 ? UInt32(self[idx]) : 0
            result.append(val)
        }

        for _ in result.count..<MemoryLayout<UInt32>.size {
            result.append(0)
        }

        return result
    }

    func toUInt64Array() -> Array<UInt64> {
        var result = Array<UInt64>()
        result.reserveCapacity(32)
        for idx in stride(from: self.startIndex, to: self.endIndex, by: MemoryLayout<UInt64>.size) {
            var val:UInt64 = 0
            val |= self.count > 7 ? UInt64(self[idx.advanced(by: 7)]) << 56 : 0
            val |= self.count > 6 ? UInt64(self[idx.advanced(by: 6)]) << 48 : 0
            val |= self.count > 5 ? UInt64(self[idx.advanced(by: 5)]) << 40 : 0
            val |= self.count > 4 ? UInt64(self[idx.advanced(by: 4)]) << 32 : 0
            val |= self.count > 3 ? UInt64(self[idx.advanced(by: 3)]) << 24 : 0
            val |= self.count > 2 ? UInt64(self[idx.advanced(by: 2)]) << 16 : 0
            val |= self.count > 1 ? UInt64(self[idx.advanced(by: 1)]) << 8 : 0
            val |= self.count > 0 ? UInt64(self[idx.advanced(by: 0)]) << 0 : 0
            result.append(val)
        }

        for _ in result.count..<MemoryLayout<UInt64>.size {
            result.append(0)
        }

        return result
    }

    /// Initialize integer from array of bytes. Caution: may be slow!
    func toInteger<T:Integer>() -> T where T: ByteConvertible, T: BitshiftOperationsType {
        if self.count == 0 {
            return 0;
        }

        var bytes = self.reversed() //FIXME: check it this is equivalent of Array(...)
        if bytes.count < MemoryLayout<T>.size {
            let paddingCount = MemoryLayout<T>.size - bytes.count
            if (paddingCount > 0) {
                bytes += Array<UInt8>(repeating: 0, count: paddingCount)
            }
        }

        if MemoryLayout<T>.size == 1 {
            return T(truncatingBitPattern: UInt64(bytes[0]))
        }

        var result: T = 0
        for byte in bytes.reversed() {
            result = result << 8 | T(byte)
        }
        return result
    }
}