MAX_EXP
if (bits > MAX_EXP)
#define HEXNDIG ((MAX_EXP - MIN_EXP + 7) / 8 + 2 * MANT_DIG)
#define MPNSIZE (howmany (MAX_EXP + 2 * MANT_DIG, BITS_PER_MP_LIMB) \
if (exponent > MAX_EXP)
MAX_EXP - 4 * int_no + lead_zero);