53 lines
1.7 KiB
C
53 lines
1.7 KiB
C
/* mpn_scan0 -- Scan from a given bit position for the next clear bit.
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Copyright 1994, 1996, 2001, 2002, 2004 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP 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 GNU MP 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 GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* Argument constraints:
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1. U must sooner or later have a limb with a clear bit.
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*/
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unsigned long int
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mpn_scan0 (register mp_srcptr up,
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register unsigned long int starting_bit)
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{
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mp_size_t starting_word;
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mp_limb_t alimb;
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int cnt;
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mp_srcptr p;
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/* Start at the word implied by STARTING_BIT. */
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starting_word = starting_bit / GMP_NUMB_BITS;
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p = up + starting_word;
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alimb = *p++ ^ GMP_NUMB_MASK;
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/* Mask off any bits before STARTING_BIT in the first limb. */
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alimb &= - (mp_limb_t) 1 << (starting_bit % GMP_NUMB_BITS);
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while (alimb == 0)
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alimb = *p++ ^ GMP_NUMB_MASK;
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count_trailing_zeros (cnt, alimb);
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return (p - up - 1) * GMP_NUMB_BITS + cnt;
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}
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