Easy way to keeping angles between -179 and 180 degrees

Question

Is there an easy way to convert an angle (in degrees) to be between -179 and 180? I\'m sure I could use mod (%) and some if statements, but it gets ugly:

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Answer 1

I don't know much Java, but I came across the same problem in Python. Most of the answers here were either for integers so I figured I'd add one that allows for floats.

def half_angle(degree):
    return -((180 - degree) % 360) + 180

Based off the other answers I'm guessing the function would looks something like this in Java (feel free to correct me)

int halfAngle(int degree) {
    return -Math.floorMod(180 - degree, 360) + 180
}

double halfAngle(double degree) {
    // Java doesn't have a built-in modulus operator
    // And Math.floorMod only works on integers and longs
    // But we can use ((x%n) + n)%n to obtain the modulus for float
    return -(((180 - degree) % 360 + 360) % 360) + 180
}

Replace int with float to your liking.

This works for any degree, both positive and negative and floats and integers:

half_angle(180) == 180
half_angle(180.1) == -179.9  // actually -179.89999999999998
half_angle(-179.9) == -179.9
half_angle(-180) = 180
half_angle(1) = 1
half_angle(0) = 0
half_angle(-1) = -1

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Math explanation:

Because the modulo operator is open at the upper end, the value x % 360 is in the range [0, 360), so by using the negative angle, the upper end becomes the lower end. So -(-x%360) is in (-360, 0], and -(-x%360)+360 is in (0, 360].

Shifting this by 180 gives us the answer.