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: }
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