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  1. // Exponentiation operator. (2.00)
  2.  
  3. import Foundation
  4.  
  5. precedencegroup ExponentiationPrecedence {
  6.     associativity: right
  7.     higherThan: MultiplicationPrecedence
  8. }
  9.  
  10. infix operator ** : ExponentiationPrecedence
  11.  
  12. func ** <T: BinaryFloatingPoint>(_ x: T, _ y: T) -> Double {
  13.     return pow(Double(x), Double(y))
  14. }
  15.  
  16. func ** <T: BinaryInteger>(_ x: T, _ y: T) -> Int {
  17.     let base = Int(x)
  18.     let expt = Int(y)
  19.  
  20.     if base == 0 || base == 1 {
  21.         return base
  22.     }
  23.     if base == -1 {
  24.         return expt % 2 == 0 ? 1 : -1
  25.     }
  26.     if expt < 0 {
  27.         return 0
  28.     }
  29.  
  30.     func detail(_ base: Int, _ expt: Int) -> Int {
  31.         switch expt {
  32.         case 0:
  33.             return 1
  34.         case 1:
  35.             return base
  36.         case _ where expt % 2 == 0:
  37.             return detail(base * base, expt / 2)
  38.         default:
  39.             return base * detail(base, expt - 1)
  40.         }
  41.     }
  42.  
  43.     return detail(base, expt)
  44. }
  45.  
  46. // Test.
  47.  
  48. func check<T: Equatable>(_ f: () -> Any, expect: T) {
  49.     let result = f()
  50.     print(result, terminator: "\t")
  51.     if let x = result as? T {
  52.         print(x == expect ? "Pass." : "Fail: \(expect)")
  53.     } else {
  54.         print("Fail: \(type(of: result)) not \(T.self)")
  55.     }
  56. }
  57.  
  58. #if DEBUG
  59. check({2 ** 0},          expect: 2)
  60. check({2 ** Int8(1)},    expect: 2.0)
  61. check({2.0 ** 2},        expect: 4)
  62. #endif
  63.  
  64. check({0 ** 0},          expect: 0)
  65. check({0 ** 1},          expect: 0)
  66. check({1 ** 0},          expect: 1)
  67. check({1 ** 1},          expect: 1)
  68. check({1 ** -1},         expect: 1)
  69. check({1 ** -2},         expect: 1)
  70.  
  71. check({-1 ** 0},         expect: 1)
  72. check({-1 ** 1},         expect: -1)
  73. check({-1 ** 2},         expect: 1)
  74. check({-1 ** -1},        expect: -1)
  75. check({-1 ** -2},        expect: 1)
  76.  
  77. check({-2 ** 0},         expect: 1)
  78. check({-2 ** 1},         expect: -2)
  79. check({-2 ** 2},         expect: 4)
  80. check({-2 ** -1},        expect: 0)
  81. check({-2 ** -2},        expect: 0)
  82.  
  83. check({2 ** 0},          expect: 1)
  84. check({2 ** Int8(1)},    expect: 2)
  85. check({2.0 ** 2},        expect: 4.0)
  86. check({2.0 ** Float(3)}, expect: 8.0)
  87. check({2 ** 4.0},        expect: 16.0)
  88. check({2.0 ** 5.0},      expect: 32.0)
  89. check({2 * 2 ** 4 * 2},  expect: 64)
Success #stdin #stdout 0.02s 21224KB
comments (?)
stdin 
Standard input is empty
stdout 
0	Pass.
0	Pass.
1	Pass.
1	Pass.
1	Pass.
1	Pass.
1	Pass.
-1	Pass.
1	Pass.
-1	Pass.
1	Pass.
1	Pass.
-2	Pass.
4	Pass.
0	Pass.
0	Pass.
1	Pass.
2	Pass.
4.0	Pass.
8.0	Pass.
16.0	Pass.
32.0	Pass.
64	Pass.
https://ideone.com/Bvfs3F
language:
Swift (swift 4.2.2)
created:
3 days ago
visibility:
public

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