Logarithmic function (base = 10)
Returns the logarithm of x with base 10.
log10f returns a Not a Nuber(NaN) and sets macro EDOM to global variable errno if x is negative. If x is zero, it returns - and sets macro ERANGE to global variable errno.
This function calculates the logarithm of x with base 10. This is realized by "log (x) / log (10)".