Add round_near_x support for small arguments.

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@3551 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 5 insertions, 0 deletions

diff --git a/atan.c b/atan.c
index c48a25318..8847c6f58 100644
--- a/atan.c
+++ b/atan.c
@@ -223,6 +223,11 @@ mpfr_atan (mpfr_ptr atan, mpfr_srcptr x, mp_rnd_t rnd_mode)
       return inexact;
     }
 
+  /* atan(x) = x - x^3/3 + x^5/5... 
+     so the error is < 2^(3*EXP(x)-1) 
+     so `EXP(x)-(3*EXP(x)-1)` = -2*EXP(x)+1 */
+  MPFR_FAST_COMPUTE_IF_SMALL_INPUT (atan,x, -2*MPFR_GET_EXP (x)+1,0,rnd_mode,);
+
   realprec = MPFR_PREC (atan) + MPFR_INT_CEIL_LOG2 (MPFR_PREC (atan)) + 4;
   /* if (MPFR_PREC (atan) + 5 > MPFR_PREC (x) && MPFR_GET_EXP (x) < 0)
     {