benchmark/single-source/ByteSwap.swift

//===--- ByteSwap.swift ---------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

// This test checks performance of Swift byte swap.
// rdar://problem/22151907

import Foundation
import TestsUtils

// a naive O(n) implementation of byteswap.
func byteswap_n(_ a: UInt64) -> UInt64 {
  return ((a & 0x00000000000000FF) << 56) |
      ((a & 0x000000000000FF00) << 40) |
      ((a & 0x0000000000FF0000) << 24) |
      ((a & 0x00000000FF000000) <<  8) |
      ((a & 0x000000FF00000000) >>  8) |
      ((a & 0x0000FF0000000000) >> 24) |
      ((a & 0x00FF000000000000) >> 40) |
      ((a & 0xFF00000000000000) >> 56)
}

// a O(logn) implementation of byteswap.
func byteswap_logn(_ a: UInt64) -> UInt64 {
  var a = a
  a = (a & 0x00000000FFFFFFFF) << 32 | (a & 0xFFFFFFFF00000000) >> 32
  a = (a & 0x0000FFFF0000FFFF) << 16 | (a & 0xFFFF0000FFFF0000) >> 16
  a = (a & 0x00FF00FF00FF00FF) << 8  | (a & 0xFF00FF00FF00FF00) >> 8
  return a
}

@inline(never)
public func run_ByteSwap(_ N: Int) {
  for _ in 1...100*N {
    // Check some results.
    CheckResults(byteswap_logn(byteswap_n(2457)) == 2457, "Incorrect results in ByteSwap.")
    CheckResults(byteswap_logn(byteswap_n(9129)) == 9129, "Incorrect results in ByteSwap.")
    CheckResults(byteswap_logn(byteswap_n(3333)) == 3333, "Incorrect results in ByteSwap.")
  }
}