added comment

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@1589 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 3 insertions, 0 deletions

diff --git a/init2.c b/init2.c
index d64a64703..2b516df1b 100644
--- a/init2.c
+++ b/init2.c
@@ -29,6 +29,9 @@ mpfr_init2 (mpfr_ptr x, mp_prec_t p)
 {
   mp_size_t xsize;
 
+  /* p=1 is not allowed since the rounding to nearest even rule requires at
+     least two bits of mantissa: the neighbours of 3/2 are 1*2^0 and 1*2^1,
+     which both have an odd mantissa */
   MPFR_ASSERTN(p >= MPFR_PREC_MIN && p <= MPFR_PREC_MAX);
 
   xsize = (mp_size_t) ((p - 1) / BITS_PER_MP_LIMB) + 1;