added acos (from Mathieu Dutour)

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@1618 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 124 insertions, 0 deletions

diff --git a/acos.c b/acos.c
new file mode 100644
index 000000000..ffbebd6b1
--- /dev/null
+++ b/acos.c
@@ -0,0 +1,124 @@
+/* mpfr_acos -- arc-cosinus of a floating-point number
+
+Copyright (C) 2001 Free Software Foundation.
+
+This file is part of the MPFR Library, and was contributed by Mathieu Dutour.
+
+The MPFR Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or (at your
+option) any later version.
+
+The MPFR Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the MPFR Library; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "mpfr.h"
+#include "mpfr-impl.h"
+
+int
+mpfr_acos (mpfr_ptr acos, mpfr_srcptr x, mp_rnd_t rnd_mode)
+{
+  mpfr_t xp;
+  mpfr_t arcc;
+
+  int signe, suplement;
+
+  mpfr_t tmp;
+  int Prec;
+  int prec_acos;
+  int good = 0;
+  int realprec;
+  int compared;
+  int inexact = 0;
+
+  /* Trivial cases */
+  if (MPFR_IS_NAN(x) || MPFR_IS_INF(x))
+    {
+      MPFR_SET_NAN(acos);
+      MPFR_RET_NAN;
+    }
+
+  /* Set x_p=|x| */
+  signe = MPFR_SIGN(x);
+  mpfr_init2 (xp, MPFR_PREC(x));
+  mpfr_abs (xp, x, rnd_mode);
+
+  compared = mpfr_cmp_ui (xp, 1);
+
+  if (compared > 0) /* acos(x) = NaN for x > 1 */
+    {
+      MPFR_SET_NAN(acos);
+      MPFR_RET_NAN;
+    }
+
+  if (compared == 0)
+    {
+      if (signe > 0) /* acos(+1) = 0 */
+	return mpfr_set_ui (acos, 0, rnd_mode);
+      else /* acos(-1) = Pi */
+        {
+          mpfr_const_pi (acos, rnd_mode);
+          return 1; /* inexact */
+        }
+    }
+
+  if (MPFR_IS_ZERO(x)) /* acos(0)=Pi/2 */
+    {
+      mpfr_const_pi (acos, rnd_mode);
+      MPFR_EXP(acos)--;
+      return 1; /* inexact */
+    }
+
+  prec_acos = MPFR_PREC(acos);
+  mpfr_ui_sub (xp, 1, xp, GMP_RNDD);
+  
+  if (signe > 0)
+      suplement = 2 - 2 * MPFR_EXP(xp);
+  else
+      suplement = 2 - MPFR_EXP(xp);
+
+  realprec = prec_acos + 10;
+
+  while (!good)
+    {
+      Prec = realprec+suplement;
+
+      /* Initialisation    */
+      mpfr_init2 (tmp, Prec);
+      mpfr_init2 (arcc, Prec);
+
+      mpfr_mul (tmp, x, x, GMP_RNDN);
+      mpfr_ui_sub (tmp, 1, tmp, GMP_RNDN);
+      mpfr_sqrt (tmp, tmp, GMP_RNDN);
+      mpfr_div (tmp, x, tmp, GMP_RNDN);
+      mpfr_atan (arcc, tmp, GMP_RNDN);
+      mpfr_const_pi (tmp, GMP_RNDN);
+      mpfr_div_2exp (tmp, tmp, 1, GMP_RNDN);
+      mpfr_sub (arcc, tmp, arcc, GMP_RNDN);
+
+      if (mpfr_can_round (arcc, realprec, GMP_RNDN, rnd_mode, MPFR_PREC(acos)))
+        {
+          inexact = mpfr_set (acos, arcc, rnd_mode);
+          good = 1;
+        }
+      else
+        realprec += _mpfr_ceil_log2 ((double) realprec);
+
+    mpfr_clear (tmp);
+    mpfr_clear (arcc);
+  }
+
+  mpfr_clear (xp);
+  return inexact;
+}