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43 lines
1.3 KiB
C
43 lines
1.3 KiB
C
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/* __gmpfr_int_ceil_log2 -- Integer ceil of log2(x)
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Copyright 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
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Contributed by the Arenaire and Cacao projects, INRIA.
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This file is part of the MPFR Library.
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The MPFR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the MPFR Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#define MPFR_NEED_LONGLONG_H /* for count_leading_zeros */
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#include "mpfr-impl.h"
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int
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__gmpfr_int_ceil_log2 (unsigned long n)
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{
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if (MPFR_UNLIKELY (n == 1))
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return 0;
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else
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{
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int b;
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mp_limb_t limb;
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MPFR_ASSERTN (n > 1);
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limb = n - 1;
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MPFR_ASSERTN (limb == n - 1);
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count_leading_zeros (b, limb);
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return BITS_PER_MP_LIMB - b;
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}
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}
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