add_ssaaaa
#define __FP_FRAC_ADDI_2(xh, xl, i) add_ssaaaa(xh, xl, xh, xl, 0, i)
#define __FP_FRAC_ADD_2 add_ssaaaa
#if !defined(add_ssaaaa)
add_ssaaaa(n1, n0, r - d0,