optimized itoa function

Question

I am thinking on how to implement the conversion of an integer (4byte, unsigned) to string with SSE instructions. The usual routine is to divide the number and store it in a loc

Answer 1

For unsigned 0 to 9,999,999 with terminating null. (99,999,999 without)

void itoa(uint64_t u, char *out) // up to 9,999,999 with terminating zero
{
    *out = 0;
    do { 
        uint64_t n0 = u;
        *((uint64_t *)out) = (*((uint64_t *)out) << 8) | (n0 + '0' - (u /= 10) * 10);
    } while (u);
}