diff options
Diffstat (limited to 'src/sqrt.c')
| -rw-r--r-- | src/sqrt.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/src/sqrt.c b/src/sqrt.c index 0477c389d..6d2f50740 100644 --- a/src/sqrt.c +++ b/src/sqrt.c @@ -152,8 +152,13 @@ mpfr_sqrt1 (mpfr_ptr r, mpfr_srcptr u, mpfr_rnd_t rnd_mode) { if (rnd_mode == MPFR_RNDN) { + /* The smallest positive number is 0.5^2^emin, and its predecessor + with unbounded exponent range is (1-2^(-p))*2^(emin-1), thus if + the result is >= the rounding boundary (1-2^(-p-1))*2^(emin-1), + there is no underflow. */ if ((exp_r == __gmpfr_emin - 1) && (rp[0] == ~mask) && rb) goto rounding; /* no underflow */ + /* If the result is <= 0.5^2^(emin-1), we should round to 0. */ if (exp_r < __gmpfr_emin - 1 || (rp[0] == MPFR_LIMB_HIGHBIT && sb == 0)) rnd_mode = MPFR_RNDZ; } |