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Annotation of OpenXM_contrib/gmp/mpz/cong_2exp.c, Revision 1.1

1.1     ! ohara       1: /* mpz_congruent_2exp_p -- test congruence of mpz mod 2^n.
        !             2:
        !             3: Copyright 2001, 2002 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 Lesser General Public License as published by
        !             9: the Free Software Foundation; either version 2.1 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 Lesser General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Lesser 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:
        !            25:
        !            26: int
        !            27: mpz_congruent_2exp_p (mpz_srcptr a, mpz_srcptr c, unsigned long d)
        !            28: {
        !            29:   unsigned long  i, dlimbs, dbits;
        !            30:   mp_ptr         ap, cp;
        !            31:   mp_limb_t      dmask, alimb, climb, sum;
        !            32:   mp_size_t      asize_signed, csize_signed, asize, csize;
        !            33:
        !            34:   if (ABSIZ(a) < ABSIZ(c))
        !            35:     MPZ_SRCPTR_SWAP (a, c);
        !            36:
        !            37:   dlimbs = d / GMP_NUMB_BITS;
        !            38:   dbits = d % GMP_NUMB_BITS;
        !            39:   dmask = (CNST_LIMB(1) << dbits) - 1;
        !            40:
        !            41:   ap = PTR(a);
        !            42:   cp = PTR(c);
        !            43:
        !            44:   asize_signed = SIZ(a);
        !            45:   asize = ABS(asize_signed);
        !            46:
        !            47:   csize_signed = SIZ(c);
        !            48:   csize = ABS(csize_signed);
        !            49:
        !            50:   if (csize_signed == 0)
        !            51:     goto a_zeros;
        !            52:
        !            53:   if ((asize_signed ^ csize_signed) >= 0)
        !            54:     {
        !            55:       /* same signs, direct comparison */
        !            56:
        !            57:       /* a==c for limbs in common */
        !            58:       if (mpn_cmp (ap, cp, MIN (csize, dlimbs)) != 0)
        !            59:         return 0;
        !            60:
        !            61:       /* if that's all of dlimbs, then a==c for remaining bits */
        !            62:       if (csize > dlimbs)
        !            63:         return ((ap[dlimbs]-cp[dlimbs]) & dmask) == 0;
        !            64:
        !            65:     a_zeros:
        !            66:       /* a remains, need all zero bits */
        !            67:
        !            68:       /* if d covers all of a and c, then must be exactly equal */
        !            69:       if (asize <= dlimbs)
        !            70:         return asize == csize;
        !            71:
        !            72:       /* whole limbs zero */
        !            73:       for (i = csize; i < dlimbs; i++)
        !            74:         if (ap[i] != 0)
        !            75:           return 0;
        !            76:
        !            77:       /* partial limb zero */
        !            78:       return (ap[dlimbs] & dmask) == 0;
        !            79:     }
        !            80:   else
        !            81:     {
        !            82:       /* different signs, negated comparison */
        !            83:
        !            84:       /* common low zero limbs, stopping at first non-zeros, which must
        !            85:          match twos complement */
        !            86:       i = 0;
        !            87:       for (;;)
        !            88:         {
        !            89:           ASSERT (i < csize);  /* always have a non-zero limb on c */
        !            90:           alimb = ap[i];
        !            91:           climb = cp[i];
        !            92:           sum = (alimb + climb) & GMP_NUMB_MASK;
        !            93:
        !            94:           if (i >= dlimbs)
        !            95:             return (sum & dmask) == 0;
        !            96:           i++;
        !            97:
        !            98:           /* require both zero, or first non-zeros as twos-complements */
        !            99:           if (sum != 0)
        !           100:             return 0;
        !           101:
        !           102:           if (alimb != 0)
        !           103:             break;
        !           104:         }
        !           105:
        !           106:       /* further limbs matching as ones-complement */
        !           107:       for (;;)
        !           108:         {
        !           109:           if (i >= csize)
        !           110:             break;
        !           111:
        !           112:           alimb = ap[i];
        !           113:           climb = cp[i];
        !           114:           sum = (alimb + climb + 1) & GMP_NUMB_MASK;
        !           115:
        !           116:           if (i >= dlimbs)
        !           117:             return (sum & dmask) == 0;
        !           118:
        !           119:           if (sum != 0)
        !           120:             return 0;
        !           121:
        !           122:           i++;
        !           123:         }
        !           124:
        !           125:       /* no more c, so require all 1 bits in a */
        !           126:
        !           127:       if (asize < dlimbs)
        !           128:         return 0;   /* not enough a */
        !           129:
        !           130:       /* whole limbs */
        !           131:       for ( ; i < dlimbs; i++)
        !           132:         if (ap[i] != GMP_NUMB_MAX)
        !           133:           return 0;
        !           134:
        !           135:       /* if only whole limbs, no further fetches from a */
        !           136:       if (dbits == 0)
        !           137:         return 1;
        !           138:
        !           139:       /* need enough a */
        !           140:       if (asize == dlimbs)
        !           141:         return 0;
        !           142:
        !           143:       return ((ap[dlimbs]+1) & dmask) == 0;
        !           144:     }
        !           145: }