improved choice of initial precision

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@621 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 3 insertions, 1 deletions

diff --git a/log.c b/log.c
index 3405e267f..5cda5403d 100644
--- a/log.c
+++ b/log.c
@@ -78,7 +78,9 @@ mpfr_log()
   if (ref<0)
     ref=-ref;
 
-  p=q+4;
+  /* use initial precision about q+lg(q)+5 */
+  p=q+5; m=q; while (m) { p++; m >>= 1; }
+
   /* adjust to entire limb */
   if (p%BITS_PER_MP_LIMB) p += BITS_PER_MP_LIMB - (p%BITS_PER_MP_LIMB);