1 /* mpz_congruent_2exp_p -- test congruence of mpz mod 2^n.
3 Copyright 2001, 2002 Free Software Foundation, Inc.
5 This file is part of the GNU MP Library.
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 3 of the License, or (at your
10 option) any later version.
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.
17 You should have received a copy of the GNU Lesser General Public License
18 along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
25 mpz_congruent_2exp_p (mpz_srcptr a
, mpz_srcptr c
, mp_bitcnt_t d
) __GMP_NOTHROW
30 mp_limb_t dmask
, alimb
, climb
, sum
;
31 mp_size_t asize_signed
, csize_signed
, asize
, csize
;
33 if (ABSIZ(a
) < ABSIZ(c
))
34 MPZ_SRCPTR_SWAP (a
, c
);
36 dlimbs
= d
/ GMP_NUMB_BITS
;
37 dbits
= d
% GMP_NUMB_BITS
;
38 dmask
= (CNST_LIMB(1) << dbits
) - 1;
43 asize_signed
= SIZ(a
);
44 asize
= ABS(asize_signed
);
46 csize_signed
= SIZ(c
);
47 csize
= ABS(csize_signed
);
49 if (csize_signed
== 0)
52 if ((asize_signed
^ csize_signed
) >= 0)
54 /* same signs, direct comparison */
56 /* a==c for limbs in common */
57 if (mpn_cmp (ap
, cp
, MIN (csize
, dlimbs
)) != 0)
60 /* if that's all of dlimbs, then a==c for remaining bits */
62 return ((ap
[dlimbs
]-cp
[dlimbs
]) & dmask
) == 0;
65 /* a remains, need all zero bits */
67 /* if d covers all of a and c, then must be exactly equal */
69 return asize
== csize
;
71 /* whole limbs zero */
72 for (i
= csize
; i
< dlimbs
; i
++)
76 /* partial limb zero */
77 return (ap
[dlimbs
] & dmask
) == 0;
81 /* different signs, negated comparison */
83 /* common low zero limbs, stopping at first non-zeros, which must
84 match twos complement */
88 ASSERT (i
< csize
); /* always have a non-zero limb on c */
91 sum
= (alimb
+ climb
) & GMP_NUMB_MASK
;
94 return (sum
& dmask
) == 0;
97 /* require both zero, or first non-zeros as twos-complements */
105 /* further limbs matching as ones-complement */
113 sum
= (alimb
+ climb
+ 1) & GMP_NUMB_MASK
;
116 return (sum
& dmask
) == 0;
124 /* no more c, so require all 1 bits in a */
127 return 0; /* not enough a */
130 for ( ; i
< dlimbs
; i
++)
131 if (ap
[i
] != GMP_NUMB_MAX
)
134 /* if only whole limbs, no further fetches from a */
142 return ((ap
[dlimbs
]+1) & dmask
) == 0;