Integer overflow gives EXC_BAD_INSTRUCTION in Swift

Question

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.

Foltz

I found this by googling "Swift integer overflow": developer.apple.com/library/ios/documentation/Swift/Conceptual/… – Merrifield

Answer 1

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

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

Winshell

Hmmm, I see. Unintuitive error message though. Thanks – Foltz