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diff --git a/mpfr/fits_u.h b/mpfr/fits_u.h
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+/* mpfr_fits_*_p -- test whether an mpfr fits a C unsigned type.
+
+Copyright 2003, 2004, 2005, 2006, 2007, 2008, 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 2.1 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, write to
+the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
+MA 02110-1301, USA. */
+
+#include "mpfr-impl.h"
+
+int
+FUNCTION (mpfr_srcptr f, mp_rnd_t rnd)
+{
+  mp_exp_t exp;
+  mp_prec_t prec;
+  TYPE s;
+  mpfr_t x;
+  int res;
+
+  if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (f)))
+    /* Zero always fit */
+    return MPFR_IS_ZERO (f) ? 1 : 0;
+  else if (MPFR_IS_NEG (f))
+    /* Negative numbers doesn't fit */
+    return 0;
+  /* now it fits if
+     (a) f <= MAXIMUM
+     (b) round(f, prec(slong), rnd) <= MAXIMUM */
+
+  exp = MPFR_GET_EXP (f);
+  if (exp < 1)
+    return 1; /* |f| < 1: always fits */
+
+  /* first compute prec(MAXIMUM) */
+  for (s = MAXIMUM, prec = 0; s != 0; s /= 2, prec ++);
+
+  /* MAXIMUM needs prec bits, i.e. 2^(prec-1) <= |MAXIMUM| < 2^prec */
+
+   /* if exp < prec - 1, then f < 2^(prec-1) < |MAXIMUM| */
+  if ((mpfr_prec_t) exp < prec - 1)
+    return 1;
+
+  /* if exp > prec + 1, then f >= 2^prec > MAXIMUM */
+  if ((mpfr_prec_t) exp > prec + 1)
+    return 0;
+
+  /* remains cases exp = prec-1 to prec+1 */
+
+  /* hard case: first round to prec bits, then check */
+  mpfr_init2 (x, prec);
+  mpfr_set (x, f, rnd);
+  res = mpfr_cmp_ui (x, MAXIMUM) <= 0;
+  mpfr_clear (x);
+
+  return res;
+}
+