[tests/tsqrt.c] improved coverage

[src/sqrt.c] added comments


git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@12292 280ebfd0-de03-0410-8827-d642c229c3f4

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;
         }