double __log10 (
  double val);   /* value to take common logarithm of */

The __log10 debugger function calculates the common logarithm for the floating-point number val. The logarithm is the exponent to which the base (10 in the case of common logs) must be raised to equal val. Or,

log₁₀ 10^x = val

For example,

log10(120)
= log10(10² × 1.2)
= 2 + log10(1.2)
≈ 2 + 0.079181 or 2.079181

The __log10 function returns the floating-point common logarithm of val.

__exp, __log

> __log10(1000);