diff options
| -rw-r--r-- | get_sj.c | 15 |
1 files changed, 10 insertions, 5 deletions
@@ -94,7 +94,12 @@ mpfr_get_sj (mpfr_srcptr f, mpfr_rnd_t rnd) } else if (MPFR_IS_POS (x)) { - for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0; n--) + /* Note: testing the condition sh >= 0 is necessary to avoid + an undefined behavior on xp[n] >> S when S >= GMP_NUMB_BITS + (even though xp[n] == 0 in such a case). This can happen if + sizeof(mp_limb_t) < sizeof(intmax_t) and |x| is small enough + because of the trailing bits due to its normalization. */ + for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--) { sh -= GMP_NUMB_BITS; /* Note the concerning the casts below: @@ -104,7 +109,7 @@ mpfr_get_sj (mpfr_srcptr f, mpfr_rnd_t rnd) for the case sizeof(intmax_t) == sizeof(mp_limb_t), as mp_limb_t is unsigned, therefore not representable as an intmax_t when the MSB is 1 (this is the case here). */ - MPFR_ASSERTD (-sh < GMP_NUMB_BITS); + MPFR_ASSERTD (sh < GMP_NUMB_BITS && -sh < GMP_NUMB_BITS); r += (sh >= 0 ? (intmax_t) xp[n] << sh : (intmax_t) (xp[n] >> (-sh))); @@ -112,11 +117,11 @@ mpfr_get_sj (mpfr_srcptr f, mpfr_rnd_t rnd) } else { - for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0; n--) + /* See the comments for the case x positive. */ + for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--) { sh -= GMP_NUMB_BITS; - /* See above for the note concerning the casts. */ - MPFR_ASSERTD (-sh < GMP_NUMB_BITS); + MPFR_ASSERTD (sh < GMP_NUMB_BITS && -sh < GMP_NUMB_BITS); r -= (sh >= 0 ? (intmax_t) xp[n] << sh : (intmax_t) (xp[n] >> (-sh))); |