Function log10 

pub fn log10(x: f64) -> f64

Base-10 logarithm, fdlibm’s __ieee754_log10.

Writes x = 2^n * m, with m in [1, 2), or in [1/2, 1) and n one higher when the exponent is negative, and returns n * log10_2hi + (n * log10_2lo + log(m) / ln 10), with log for log(m). Special cases as log.