small improvement in sign detection

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@3880 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 5 insertions, 3 deletions

diff --git a/sin_cos.c b/sin_cos.c
index 22a25bf47..ec822fd9f 100644
--- a/sin_cos.c
+++ b/sin_cos.c
@@ -62,8 +62,10 @@ mpfr_sin_cos (mpfr_ptr y, mpfr_ptr z, mpfr_srcptr x, mp_rnd_t rnd_mode)
   mpfr_init2 (c, m);
 
   /* first determine sign of sinus */
-  if (MPFR_GET_EXP (x) > 0)
+  if (MPFR_GET_EXP (x) > 1) /* |x| >= 2 */
     {
+      /* FIXME: we can start with a small precision,
+	 and increase until we can decide the sign. */
       mpfr_init2 (k, m);
       mpfr_const_pi (c, GMP_RNDN);
       mpfr_mul_2ui (c, c, 1, GMP_RNDN);    /* 2*Pi */
@@ -75,7 +77,7 @@ mpfr_sin_cos (mpfr_ptr y, mpfr_ptr z, mpfr_srcptr x, mp_rnd_t rnd_mode)
       neg = mpfr_cmp (k, c) > 0;
       mpfr_clear (k);
     }
-  else
+  else /* if EXP(x) <= 1, then |x| < 2, thus sign(sin(x)) = sign(x) */
     neg = MPFR_IS_NEG (x);
 
   MPFR_ZIV_INIT (loop, m);
@@ -83,7 +85,7 @@ mpfr_sin_cos (mpfr_ptr y, mpfr_ptr z, mpfr_srcptr x, mp_rnd_t rnd_mode)
     {
       mpfr_cos (c, x, GMP_RNDZ);
       if (!mpfr_can_round (c, m, GMP_RNDZ, rnd_mode, MPFR_PREC (z)))
-        goto next_step;
+	goto next_step;
       mpfr_set (z, c, rnd_mode);
       mpfr_sqr (c, c, GMP_RNDU);
       mpfr_ui_sub (c, 1, c, GMP_RNDN);