diff options
| -rw-r--r-- | src/get_sj.c | 35 |
1 files changed, 16 insertions, 19 deletions
diff --git a/src/get_sj.c b/src/get_sj.c index 417158926..4554fdc96 100644 --- a/src/get_sj.c +++ b/src/get_sj.c @@ -83,14 +83,15 @@ mpfr_get_sj (mpfr_srcptr f, mpfr_rnd_t rnd) MPFR_ASSERTN (MPFR_IS_NEG (x) && mpfr_powerof2_raw (x)); r = MPFR_INTMAX_MIN; } - else if (MPFR_IS_POS (x)) + /* sh is the number of bits the remain to be considered in {xp, xn} */ + else { - /* Note: testing the condition sh >= 0 is necessary to avoid + /* 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--) + for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh > 0; n--) { sh -= GMP_NUMB_BITS; /* Note the concerning the casts below: @@ -100,23 +101,19 @@ 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 && -sh < GMP_NUMB_BITS); - r += (sh >= 0 - ? (intmax_t) xp[n] << sh - : (intmax_t) (xp[n] >> (-sh))); - } - } - else - { - /* See the comments for the case x positive. */ - for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--) - { - 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))); + /* sh + GMP_NUMB_BITS <= prec + 1 because if sh >= 0 the shifted + value xp[n] << sh should fit in an intmax_t */ + MPFR_ASSERTD (sh + GMP_NUMB_BITS <= prec + 1); + MPFR_ASSERTD (-sh < GMP_NUMB_BITS); + if (sh >= 0) MPFR_ASSERTN(0); + /* each limb should be shifted by sh bits to the left if sh>=0, + and by sh bits to the right if sh < 0 */ + r += sh >= 0 + ? (intmax_t) xp[n] << sh + : (intmax_t) (xp[n] >> (-sh)); } + if (MPFR_IS_NEG(x)) + r = -r; } } |