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xcode - Integer overflow gives EXC_BAD_INSTRUCTION in Swift

While messing around with Swift, I noticed that when the 64 bit integer overflows, I get the following error:

file:///Users/user/Documents/playground/MyPlayground.playground/: error: Playground execution aborted: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).

func fibonacci(which: Int) -> (fibOf: Int, isEqualTo: Int) {
    var i = 1, j = 1

    for var k = 2; k < which; k += 1 {
        let tmp = i + j // this line is highlighted when error occurs
        j = i
        i = tmp
    }

    return (which, i)
}

print (fibonacci(92))
print (fibonacci(93)) // this triggers an error

The first call, i.e. with 92 as argument, will run fine. When supplying the 93 value however, I get the irrelevant EXC_BAD_INSTRUCTION error. Is this a bug or what? Normally I'd expect it to overflow.

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It is expected behaviour. If you want to overflow, you need to use overflow operators.

  • Overflow addition (&+)
  • Overflow subtraction (&-)
  • Overflow multiplication (&*)

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