1 files changed, 65 insertions, 0 deletions
diff --git a/min_prec.c b/min_prec.c
new file mode 100644
index 000000000..db0ae25c7
--- /dev/null
+++ b/min_prec.c
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+/* mpfr_min_prec -- minimal size in bits to hold the mantissa
+
+Copyright 2009 Free Software Foundation, Inc.
+Contributed by the Arenaire and Cacao projects, INRIA.
+
+This file is part of the GNU MPFR Library.
+
+The GNU 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 3 of the License, or (at your
+option) any later version.
+
+The GNU 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 GNU MPFR Library; see the file COPYING.LIB.  If not, see
+http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
+51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
+
+#include "mpfr-impl.h"
+
+int
+mpfr_min_prec (mpfr_srcptr x)
+{
+  mp_limb_t *mx;
+  mp_prec_t px;
+  mp_size_t n;
+  int res, i;
+
+
+  if (MPFR_IS_NAN (x) || MPFR_IS_INF (x))
+    return 0;
+
+  if (MPFR_IS_ZERO (x))
+    return 0;
+
+  mx = MPFR_MANT (x);
+  px = MPFR_PREC (x);
+
+  res = 0;
+  /* Count full limbs set to zero */
+  for (n = (px - 1) / BITS_PER_MP_LIMB; mx[n] == 0; n--)
+    {
+      res += BITS_PER_MP_LIMB;
+    }
+
+  i = 0;
+  /* mx[n] is now the first limb which is not null. Count number
+   * of null bits in mx[n], from the right */
+  while ((i < BITS_PER_MP_LIMB) && (mx[n] & (1 << i) == 0))
+    i++;
+
+  res += i;
+  /* If we have trailing zero bits because the precision
+   * is not a multiple of BITS_PER_MP_LIMB, we must not count
+   * those. */
+  i = px % BITS_PER_MP_LIMB;
+  if (px != 0)
+    res -= BITS_PER_MP_LIMB - i;
+
+  return px - res;
+}