pub fn ln(fp: FpUnit, x: f32) -> f32
ln x for x > 0: x = m·2^E with m in [3/4, 3/2), so a value near 1 keeps E = 0; m against the nearest table point c_j, and ln(m/c_j) by its quartic.
ln x
x > 0
x = m·2^E
m
[3/4, 3/2)
E = 0
c_j
ln(m/c_j)