This patch proposes adding a log10() function that works on scaled integers. The only 2 arguments are the integer itself and its scale. The result is also a scaled integer with the same scale as the input. If the true result cannot be precisely represented, it is rounded down towards negative infinity.
I think this would be a good function to complement fixed point types, although we use scaled integers here since the types are still hidden behind a flag. This function also isn't something specified in the Embedded C spec, though we would like to use it in Fuchsia with fixed point types.