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Math.pow with negative numbers and non-integer powers

The ECMAScript specification for Math.powhas the following peculiar rule:

  • If x <0 and x is finite and y is finite and y is not an integer, the result is NaN.

( http://es5.github.com/#x15.8.2.13 )

The result Math.pow(-8, 1 / 3)is NaN, not-2

What is the reason for this rule? Is there some broader computer science or IEEEish reason for this rule, or is it just a TC39 / Eich choice made one at a time?

Update

Thanks to the exchange of Amadan with me, I think I now understand the reasoning. I would like to expand our discussion for the sake of posterity.

Take the following example: Math.pow(823543, 1 / 7)gives 6.999999999999999, although it really should be 7. This is an inaccuracy due to the fact that 1 / 7you must first convert to a decimal representation 0.14285714285714285, which is truncated and loses accuracy. This is not such a bad problem when we work with positive numbers, because we still get a result that is very close to the real result.

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+5
2

, , ECMAScript . , - 1 + 1.732i, . ( , -2 , - , ).

+3

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.

func checkSquareRoot(x: Double, y: Double) -> Double {
    let result = pow(x, y)

    if x > 0 {
        return result
    } else {
        return -1 * pow( -x, y)
    }
}
0

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