[BACK]Return to cong.c CVS log [TXT][DIR] Up to [local] / OpenXM_contrib / gmp / mpz

Annotation of OpenXM_contrib/gmp/mpz/cong.c, Revision 1.1.1.1

1.1       ohara       1: /* mpz_congruent_p -- test congruence of two mpz's.
                      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: #include "longlong.h"
                     25:
                     26:
                     27: /* For big divisors this code is only very slightly better than the user
                     28:    doing a combination of mpz_sub and mpz_tdiv_r, but it's quite convenient,
                     29:    and perhaps in the future can be improved, in similar ways to
                     30:    mpn_divisible_p perhaps.
                     31:
                     32:    The csize==1 / dsize==1 special case makes mpz_congruent_p as good as
                     33:    mpz_congruent_ui_p on relevant operands, though such a combination
                     34:    probably doesn't occur often.
                     35:
                     36:    Alternatives:
                     37:
                     38:    If c<d then it'd work to just form a%d and compare a and c (either as
                     39:    a==c or a+c==d depending on the signs), but the saving from avoiding the
                     40:    abs(a-c) calculation would be small compared to the division.
                     41:
                     42:    Similarly if both a<d and c<d then it would work to just compare a and c
                     43:    (a==c or a+c==d), but this isn't considered a particularly important case
                     44:    and so isn't done for the moment.
                     45:
                     46:    Low zero limbs on d could be stripped and the corresponding limbs of a
                     47:    and c tested and skipped, but doing so would introduce a borrow when a
                     48:    and c differ in sign and have non-zero skipped limbs.  It doesn't seem
                     49:    worth the complications to do this, since low zero limbs on d should
                     50:    occur only rarely.  */
                     51:
                     52: int
                     53: mpz_congruent_p (mpz_srcptr a, mpz_srcptr c, mpz_srcptr d)
                     54: {
                     55:   mp_size_t  asize, csize, dsize, sign;
                     56:   mp_srcptr  ap, cp, dp;
                     57:   mp_ptr     xp;
                     58:   mp_limb_t  alow, clow, dlow, dmask, r;
                     59:   int        result;
                     60:   TMP_DECL (marker);
                     61:
                     62:   dsize = SIZ(d);
                     63:   if (dsize == 0)
                     64:     DIVIDE_BY_ZERO;
                     65:   dsize = ABS(dsize);
                     66:   dp = PTR(d);
                     67:
                     68:   if (ABSIZ(a) < ABSIZ(c))
                     69:     MPZ_SRCPTR_SWAP (a, c);
                     70:
                     71:   asize = SIZ(a);
                     72:   csize = SIZ(c);
                     73:   sign = (asize ^ csize);
                     74:
                     75:   asize = ABS(asize);
                     76:   ap = PTR(a);
                     77:
                     78:   if (csize == 0)
                     79:     return mpn_divisible_p (ap, asize, dp, dsize);
                     80:
                     81:   csize = ABS(csize);
                     82:   cp = PTR(c);
                     83:
                     84:   alow = ap[0];
                     85:   clow = cp[0];
                     86:   dlow = dp[0];
                     87:
                     88:   /* Check a==c mod low zero bits of dlow.  This might catch a few cases of
                     89:      a!=c quickly, and it helps the csize==1 special cases below.  */
                     90:   dmask = LOW_ZEROS_MASK (dlow) & GMP_NUMB_MASK;
                     91:   alow = (sign >= 0 ? alow : -alow);
                     92:   if (((alow-clow) & dmask) != 0)
                     93:     return 0;
                     94:
                     95:   if (csize == 1)
                     96:     {
                     97:       if (dsize == 1)
                     98:         {
                     99:         cong_1:
                    100:           if (sign < 0)
                    101:             NEG_MOD (clow, clow, dlow);
                    102:
                    103:           if (BELOW_THRESHOLD (asize, MODEXACT_1_ODD_THRESHOLD))
                    104:             {
                    105:               r = mpn_mod_1 (ap, asize, dlow);
                    106:               if (clow < dlow)
                    107:                 return r == clow;
                    108:               else
                    109:                 return r == (clow % dlow);
                    110:             }
                    111:
                    112:           if ((dlow & 1) == 0)
                    113:             {
                    114:               /* Strip low zero bits to get odd d required by modexact.  If
                    115:                  d==e*2^n then a==c mod d if and only if both a==c mod e and
                    116:                  a==c mod 2^n, the latter having been done above.  */
                    117:               unsigned  twos;
                    118:               count_trailing_zeros (twos, dlow);
                    119:               dlow >>= twos;
                    120:             }
                    121:
                    122:           r = mpn_modexact_1c_odd (ap, asize, dlow, clow);
                    123:           return r == 0 || r == dlow;
                    124:         }
                    125:
                    126:       /* dlow==0 is avoided since we don't want to bother handling extra low
                    127:          zero bits if dsecond is even (would involve borrow if a,c differ in
                    128:          sign and alow,clow!=0).  */
                    129:       if (dsize == 2 && dlow != 0)
                    130:         {
                    131:           mp_limb_t  dsecond = dp[1];
                    132:
                    133:           if (dsecond <= dmask)
                    134:             {
                    135:               unsigned   twos;
                    136:               count_trailing_zeros (twos, dlow);
                    137:               dlow = (dlow >> twos) | (dsecond << (GMP_NUMB_BITS-twos));
                    138:               ASSERT_LIMB (dlow);
                    139:
                    140:               /* dlow will be odd here, so the test for it even under cong_1
                    141:                  is unnecessary, but the rest of that code is wanted. */
                    142:               goto cong_1;
                    143:             }
                    144:         }
                    145:     }
                    146:
                    147:   TMP_MARK (marker);
                    148:   xp = TMP_ALLOC_LIMBS (asize+1);
                    149:
                    150:   /* calculate abs(a-c) */
                    151:   if (sign >= 0)
                    152:     {
                    153:       /* same signs, subtract */
                    154:       if (asize > csize || mpn_cmp (ap, cp, asize) >= 0)
                    155:         ASSERT_NOCARRY (mpn_sub (xp, ap, asize, cp, csize));
                    156:       else
                    157:         ASSERT_NOCARRY (mpn_sub_n (xp, cp, ap, asize));
                    158:       MPN_NORMALIZE (xp, asize);
                    159:     }
                    160:   else
                    161:     {
                    162:       /* different signs, add */
                    163:       mp_limb_t  carry;
                    164:       carry = mpn_add (xp, ap, asize, cp, csize);
                    165:       xp[asize] = carry;
                    166:       asize += (carry != 0);
                    167:     }
                    168:
                    169:   result = mpn_divisible_p (xp, asize, dp, dsize);
                    170:
                    171:   TMP_FREE (marker);
                    172:   return result;
                    173: }

FreeBSD-CVSweb <freebsd-cvsweb@FreeBSD.org>