CryptoSwift/Sources/CryptoSwift/UInt64+Extension.swift

//
//  UInt64Extension.swift
//  CryptoSwift
//
//  Copyright (C) 2014-2017 Marcin Krzyżanowski <marcin@krzyzanowskim.com>
//  This software is provided 'as-is', without any express or implied warranty.
//
//  In no event will the authors be held liable for any damages arising from the use of this software.
//
//  Permission is granted to anyone to use this software for any purpose,including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:
//
//  - The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation is required.
//  - Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
//  - This notice may not be removed or altered from any source or binary distribution.
//

/** array of bytes */
extension UInt64 {

    @_specialize(exported: true, where T == ArraySlice<UInt8>)
    init<T: Collection>(bytes: T) where T.Element == UInt8, T.Index == Int {
        self = UInt64(bytes: bytes, fromIndex: bytes.startIndex)
    }

    @_specialize(exported: true, where T == ArraySlice<UInt8>)
    init<T: Collection>(bytes: T, fromIndex index: T.Index) where T.Element == UInt8, T.Index == Int {
        if bytes.isEmpty {
            self = 0
            return
        }

        let count = bytes.count

        let val0 = count > 0 ? UInt64(bytes[index.advanced(by: 0)]) << 56 : 0
        let val1 = count > 0 ? UInt64(bytes[index.advanced(by: 1)]) << 48 : 0
        let val2 = count > 0 ? UInt64(bytes[index.advanced(by: 2)]) << 40 : 0
        let val3 = count > 0 ? UInt64(bytes[index.advanced(by: 3)]) << 32 : 0
        let val4 = count > 0 ? UInt64(bytes[index.advanced(by: 4)]) << 24 : 0
        let val5 = count > 0 ? UInt64(bytes[index.advanced(by: 5)]) << 16 : 0
        let val6 = count > 0 ? UInt64(bytes[index.advanced(by: 6)]) << 8 : 0
        let val7 = count > 0 ? UInt64(bytes[index.advanced(by: 7)]) : 0

        self = val0 | val1 | val2 | val3 | val4 | val5 | val6 | val7
    }
}