Constant curve25519_dalek::constants::SQRT_MINUS_HALF

pub const SQRT_MINUS_HALF: FieldElement = FieldElement([-17256545, 3971863, 28865457, -1750208, 27359696, -16640980,
              12573105, 1002827, -163343, 11073975])

SQRT_MINUS_HALF is sqrt(-1/2)