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: }
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