1 /* mpz_congruent_ui_p -- test congruence of mpz and ulong. 2 3 Copyright 2000, 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 3 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. If not, see http://www.gnu.org/licenses/. */ 19 20 #include "gmp.h" 21 #include "gmp-impl.h" 22 #include "longlong.h" 23 24 25 /* There's some explicit checks for c<d since it seems reasonably likely an 26 application might use that in a test. 27 28 Hopefully the compiler can generate something good for r==(c%d), though 29 if modexact is being used exclusively then that's not reached. */ 30 31 int 32 mpz_congruent_ui_p (mpz_srcptr a, unsigned long cu, unsigned long du) 33 { 34 mp_srcptr ap; 35 mp_size_t asize; 36 mp_limb_t c, d, r; 37 38 if (UNLIKELY (du == 0)) 39 return (mpz_cmp_ui (a, cu) == 0); 40 41 asize = SIZ(a); 42 if (asize == 0) 43 { 44 if (cu < du) 45 return cu == 0; 46 else 47 return (cu % du) == 0; 48 } 49 50 /* For nails don't try to be clever if c or d is bigger than a limb, just 51 fake up some mpz_t's and go to the main mpz_congruent_p. */ 52 if (du > GMP_NUMB_MAX || cu > GMP_NUMB_MAX) 53 { 54 mp_limb_t climbs[2], dlimbs[2]; 55 mpz_t cz, dz; 56 57 ALLOC(cz) = 2; 58 PTR(cz) = climbs; 59 ALLOC(dz) = 2; 60 PTR(dz) = dlimbs; 61 62 mpz_set_ui (cz, cu); 63 mpz_set_ui (dz, du); 64 return mpz_congruent_p (a, cz, dz); 65 } 66 67 /* NEG_MOD works on limbs, so convert ulong to limb */ 68 c = cu; 69 d = du; 70 71 if (asize < 0) 72 { 73 asize = -asize; 74 NEG_MOD (c, c, d); 75 } 76 77 ap = PTR (a); 78 79 if (ABOVE_THRESHOLD (asize, BMOD_1_TO_MOD_1_THRESHOLD)) 80 { 81 r = mpn_mod_1 (ap, asize, d); 82 if (c < d) 83 return r == c; 84 else 85 return r == (c % d); 86 } 87 88 if ((d & 1) == 0) 89 { 90 /* Strip low zero bits to get odd d required by modexact. If 91 d==e*2^n then a==c mod d if and only if both a==c mod 2^n 92 and a==c mod e. */ 93 94 unsigned twos; 95 96 if ((ap[0]-c) & LOW_ZEROS_MASK (d)) 97 return 0; 98 99 count_trailing_zeros (twos, d); 100 d >>= twos; 101 } 102 103 r = mpn_modexact_1c_odd (ap, asize, d, c); 104 return r == 0 || r == d; 105 } 106