DBL_FRACHBITS
r = 1 << DBL_FRACHBITS; /* implicit bit */
exp -= DBL_FRACHBITS;
r = 1 << DBL_FRACHBITS; /* implicit bit */
exp -= DBL_FRACHBITS;
e = i0 >> DBL_FRACHBITS;
e = ((i0 >> DBL_FRACHBITS) & 0x7ff) - DBL_EXP_BIAS;
i0 |= (1 << DBL_FRACHBITS);