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Approximates asin to within about 1e-6. This approximation
works by breaking the range from 0 to 1 into 5 regions for all
but the region nearest 1, rational polynomial models get us a
very good approximation of asin and by interpolating as we move
from region to region, we can guarantee continuity and we
happen to get monotonicity as well. for the values near 1, we
just use Math.asin as our region "approximation".