[src/sin.c] increase initial precision when x is large

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@13737 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 3 insertions, 1 deletions

diff --git a/src/sin.c b/src/sin.c
index dd7593d8b..0caed4b9f 100644
--- a/src/sin.c
+++ b/src/sin.c
@@ -82,7 +82,9 @@ mpfr_sin (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
       goto end;
     }
 
-  m = precy + MPFR_INT_CEIL_LOG2 (precy) + 7;
+  /* for x large, since argument reduction is expensive, we want to avoid
+     any failure in Ziv's strategy, thus we take into account expx too */
+  m = precy + MPFR_INT_CEIL_LOG2 (MAX(precy,expx)) + 7;
 
   /* since we compute sin(x) as sqrt(1-cos(x)^2), and for x small we have
      cos(x)^2 ~ 1 - x^2, when subtracting cos(x)^2 from 1 we will lose