CryptoSwift/Sources/CryptoSwift/Generics.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.
//

/** build bit pattern from array of bits */
@_specialize(exported: true, where T == UInt8)
func integerFrom<T: FixedWidthInteger>(_ bits: Array<Bit>) -> T {
    var bitPattern: T = 0
    for idx in bits.indices {
        if bits[idx] == Bit.one {
            let bit = T(UInt64(1) << UInt64(idx))
            bitPattern = bitPattern | bit
        }
    }
    return bitPattern
}

/// Array of bytes. Caution: don't use directly because generic is slow.
///
/// - parameter value: integer value
/// - parameter length: length of output array. By default size of value type
///
/// - returns: Array of bytes
@_specialize(exported: true, where T == Int)
@_specialize(exported: true, where T == UInt)
@_specialize(exported: true, where T == UInt8)
@_specialize(exported: true, where T == UInt16)
@_specialize(exported: true, where T == UInt32)
@_specialize(exported: true, where T == UInt64)
func arrayOfBytes<T: FixedWidthInteger>(value: T, length totalBytes: Int = MemoryLayout<T>.size) -> Array<UInt8> {
    let valuePointer = UnsafeMutablePointer<T>.allocate(capacity: 1)
    valuePointer.pointee = value

    let bytesPointer = UnsafeMutablePointer<UInt8>(OpaquePointer(valuePointer))
    var bytes = Array<UInt8>(repeating: 0, count: totalBytes)
    for j in 0..<min(MemoryLayout<T>.size, totalBytes) {
        bytes[totalBytes - 1 - j] = (bytesPointer + j).pointee
    }

    valuePointer.deinitialize(count: 1)
    valuePointer.deallocate()

    return bytes
}