LIMBS_PER_DIGIT_IN_BASE

[Zimmermann Paul]

       Hi,

about the following macro in gmp-impl.h:

/* Compute the number of limbs corresponding to ndigits base-b digits, rounding
   up.  */
#define LIMBS_PER_DIGIT_IN_BASE(res, ndigits, b)                        \
  do {                                                                  \
    mp_limb_t _ph, _dummy;                                              \
    umul_ppmm (_ph, _dummy, mp_bases[b].log2b, (mp_limb_t) (ndigits));  \
    res = 8 * _ph / GMP_NUMB_BITS + 2;                                  \
  } while (0)

On a 32-bit machine, mp_bases[b].log2b is floor(2^32*log(b)/8/log(2)).
Thus for ndigits > 2^32*log(2)/log(b), we have _ph >= 2^32/8, and the
computation 8 * _ph in res will overflow, unless I'm wrong.

Paul