https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98076
--- Comment #9 from Francois-Xavier Coudert <fxcoudert at gcc dot gnu.org> --- After my patch, measurements seem to indicate the output of integers is mostly bound the library overhead. Inspection of the various itoa/btoa/otoa/xtoa functions seems to show they're reasonably efficient. Reading of integers is still quite inefficient. The function read_decimal() always works with the largest integer kind, performing additions and multiplications by 10. This is, I think, available in hardware (not library call). read_radix() is probably also quite inefficient. It is written in a completely generic fashion, although it operates on fixed radices (2, 8 or 16); such multiplications could be done by bit shift. Even if we told the compilers that the radix was 2, 8 or 16 in each case (three functions), it would optimise the multiplications into bit shifts itself.
