new function mpfr_get_f

git-svn-id: svn://scm.gforge.inria.fr/svn/mpfr/trunk@3365 280ebfd0-de03-0410-8827-d642c229c3f4

1 files changed, 96 insertions, 0 deletions

diff --git a/get_f.c b/get_f.c
new file mode 100644
index 000000000..0ce81d311
--- /dev/null
+++ b/get_f.c
@@ -0,0 +1,96 @@
+/* mpfr_get_f -- convert a MPFR number to a GNU MPF number
+
+Copyright 2005 Free Software Foundation, Inc.
+
+This file is part of the MPFR Library.
+
+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 "mpfr-impl.h"
+
+/* return value is 0 iff no error occurred in the conversion
+   (1 for NaN, +Inf, -Inf that have no equivalent in mpf)
+*/
+int
+mpfr_get_f (mpf_ptr x, mpfr_srcptr y, mp_rnd_t rnd_mode)
+{
+  unsigned long sx, sy, precx, precy, sh;
+  mp_exp_t ey;
+
+  if (MPFR_UNLIKELY(MPFR_IS_SINGULAR(y)))
+    {
+      if (MPFR_IS_ZERO(y))
+        {
+          mpf_set_ui (x, 0);
+          return 0;
+        }
+      else /* NaN or Inf */
+        return 1;
+    }
+
+  sx = PREC(x); /* number of limbs of the mantissa of x */
+
+  precy = MPFR_PREC(y);
+  precx = sx * BITS_PER_MP_LIMB;
+  sy = 1 + (MPFR_PREC(y) - 1) / BITS_PER_MP_LIMB;
+
+  /* since mpf numbers are represented in base 2^BITS_PER_MP_LIMB,
+     we loose -EXP(y) % BITS_PER_MP_LIMB bits in the most significant limb */
+  ey = MPFR_GET_EXP(y) % BITS_PER_MP_LIMB;
+  if (ey <= 0)
+    sh = (unsigned long) (-ey);
+  else /* 0 < ey < BITS_PER_MP_LIMB */
+    sh = BITS_PER_MP_LIMB - (unsigned long) ey;
+  if (precy + sh <= precx) /* we can copy directly */
+    {
+      /* necessarily sy <= sx */
+      if (sh)
+        mpn_rshift (PTR(x) + sx - sy, MPFR_MANT(y), sy, sh);
+      else
+        MPN_COPY (PTR(x) + sx - sy, MPFR_MANT(y), sy);
+      if (sx > sy)
+        MPN_ZERO (PTR(x), sx - sy);
+      EXP(x) = (MPFR_GET_EXP(y) + sh) / BITS_PER_MP_LIMB;
+    }
+  else /* we have to round to precx - sh bits */
+    {
+      mpfr_t z;
+      unsigned long sz;
+
+      mpfr_init2 (z, precx - sh);
+      sz = 1 + (MPFR_PREC(z) - 1) / BITS_PER_MP_LIMB;
+      mpfr_set (z, y, rnd_mode);
+      /* warning, sh may change due to rounding, but then z is a power of two,
+         thus we can safely ignore its last bit which is 0 */
+      ey = MPFR_GET_EXP(z) % BITS_PER_MP_LIMB;
+      sh = (ey <= 0) ? (unsigned long) (-ey)
+        : BITS_PER_MP_LIMB - (unsigned long) ey;
+      if (sh)
+        mpn_rshift (PTR(x) + sx - sz, MPFR_MANT(z), sz, sh);
+      else
+        MPN_COPY (PTR(x) + sx - sz, MPFR_MANT(z), sz);
+      if (sx > sz)
+        MPN_ZERO (PTR(x), sx - sz);
+      EXP(x) = (MPFR_GET_EXP(z) + sh) / BITS_PER_MP_LIMB;
+      mpfr_clear (z);
+    }
+
+  /* set size and sign */
+  SIZ(x) = (MPFR_FROM_SIGN_TO_INT(MPFR_SIGN(y)) < 0) ? -sx : sx;
+
+  return 0;
+}