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Annotation of OpenXM_contrib/gmp/mpn/generic/scan1.c, Revision 1.1

1.1     ! maekawa     1: /* mpn_scan1 -- Scan from a given bit position for the next set bit.
        !             2:
        !             3: Copyright (C) 1994, 1996 Free Software Foundation, Inc.
        !             4:
        !             5: This file is part of the GNU MP Library.
        !             6:
        !             7: The GNU MP Library is free software; you can redistribute it and/or modify
        !             8: it under the terms of the GNU Library General Public License as published by
        !             9: the Free Software Foundation; either version 2 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The GNU MP Library is distributed in the hope that it will be useful, but
        !            13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Library General Public License
        !            18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include "gmp.h"
        !            23: #include "gmp-impl.h"
        !            24: #include "longlong.h"
        !            25:
        !            26: /* Design issues:
        !            27:    1. What if starting_bit is not within U?  Caller's problem?
        !            28:    2. Bit index should be 'unsigned'?
        !            29:
        !            30:    Argument constraints:
        !            31:    1. U must sooner ot later have a limb != 0.
        !            32:  */
        !            33:
        !            34: unsigned long int
        !            35: #if __STDC__
        !            36: mpn_scan1 (register mp_srcptr up,
        !            37:           register unsigned long int starting_bit)
        !            38: #else
        !            39: mpn_scan1 (up, starting_bit)
        !            40:      register mp_srcptr up;
        !            41:      register unsigned long int starting_bit;
        !            42: #endif
        !            43: {
        !            44:   mp_size_t starting_word;
        !            45:   mp_limb_t alimb;
        !            46:   int cnt;
        !            47:   mp_srcptr p;
        !            48:
        !            49:   /* Start at the word implied by STARTING_BIT.  */
        !            50:   starting_word = starting_bit / BITS_PER_MP_LIMB;
        !            51:   p = up + starting_word;
        !            52:   alimb = *p++;
        !            53:
        !            54:   /* Mask off any bits before STARTING_BIT in the first limb.  */
        !            55:   alimb &= - (mp_limb_t) 1 << (starting_bit % BITS_PER_MP_LIMB);
        !            56:
        !            57:   while (alimb == 0)
        !            58:     alimb = *p++;
        !            59:
        !            60:   count_leading_zeros (cnt, alimb & -alimb);
        !            61:   return (p - up) * BITS_PER_MP_LIMB - 1 - cnt;
        !            62: }