CryptoSwift/Sources/CryptoSwift/Generics.swift

//
//  Generics.swift
//  CryptoSwift
//
//  Created by Marcin Krzyzanowski on 02/09/14.
//  Copyright (c) 2014 Marcin Krzyzanowski. All rights reserved.
//

/** Protocol and extensions for integerFrom(bits:). Bit hakish for me, but I can't do it in any other way */
protocol Initiable  {
    init(_ v: Int)
    init(_ v: UInt)
}

extension Int:Initiable {}
extension UInt:Initiable {}
extension UInt8:Initiable {}
extension UInt16:Initiable {}
extension UInt32:Initiable {}
extension UInt64:Initiable {}

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

/// Array of bytes, little-endian representation. Don't use if not necessary.
/// I found this method slow
func arrayOfBytes<T>(value:T, length:Int? = nil) -> Array<UInt8> {
    let totalBytes = length ?? MemoryLayout<T>.size

    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()
    valuePointer.deallocate(capacity: 1)
    
    return bytes
}

// MARK: - shiftLeft

// helper to be able to make shift operation on T
@_specialize(Int)
func << <T:SignedInteger>(lhs: T, rhs: Int) -> Int {
    let a = lhs as! Int
    let b = rhs
    return a << b
}

@_specialize(UInt)
func << <T:UnsignedInteger>(lhs: T, rhs: Int) -> UInt {
    let a = lhs as! UInt
    let b = rhs
    return a << b
}

// Generic function itself
// FIXME: this generic function is not as generic as I would. It crashes for smaller types
@_specialize(Int)
func shiftLeft<T: SignedInteger>(_ value: T, by count: Int) -> T where T: Initiable {
    if (value == 0) {
        return 0;
    }
    
    let bitsCount = (MemoryLayout<T>.size * 8)
    let shiftCount = Int(Swift.min(count, bitsCount - 1))
    
    var shiftedValue:T = 0;
    for bitIdx in 0..<bitsCount {
        let bit = T(IntMax(1 << bitIdx))
        if ((value & bit) == bit) {
            shiftedValue = shiftedValue | T(bit << shiftCount)
        }
    }
    
    if (shiftedValue != 0 && count >= bitsCount) {
        // clear last bit that couldn't be shifted out of range
        shiftedValue = shiftedValue & T(~(1 << (bitsCount - 1)))
    }
    return shiftedValue
}

// for any f*** other Integer type - this part is so non-Generic
func shiftLeft(_ value: UInt, by count: Int) -> UInt {
    return UInt(shiftLeft(Int(value), by: count))
}

func shiftLeft(_ value: UInt8, by count: Int) -> UInt8 {
    return UInt8(shiftLeft(UInt(value), by: count))
}

func shiftLeft(_ value: UInt16, by count: Int) -> UInt16 {
    return UInt16(shiftLeft(UInt(value), by: count))
}

func shiftLeft(_ value: UInt32, by count: Int) -> UInt32 {
    return UInt32(shiftLeft(UInt(value), by: count))
}

func shiftLeft(_ value: UInt64, by count: Int) -> UInt64 {
    return UInt64(shiftLeft(UInt(value), by: count))
}

func shiftLeft(_ value: Int8, by count: Int) -> Int8 {
    return Int8(shiftLeft(Int(value), by: count))
}

func shiftLeft(_ value: Int16, by count: Int) -> Int16 {
    return Int16(shiftLeft(Int(value), by: count))
}

func shiftLeft(_ value: Int32, by count: Int) -> Int32 {
    return Int32(shiftLeft(Int(value), by: count))
}

func shiftLeft(_ value: Int64, by count: Int) -> Int64 {
    return Int64(shiftLeft(Int(value), by: count))
}