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author | Kevin Ryde <user42@zip.com.au> | 2001-03-14 23:27:40 +0100 |
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committer | Kevin Ryde <user42@zip.com.au> | 2001-03-14 23:27:40 +0100 |
commit | 95d98dfc07bd04667064b40aa9da72f5605e1cd8 (patch) | |
tree | f242926f3d4f141c146d04937f05a9b59bd791c5 /mpz/cong_2exp.c | |
parent | ed34f9c4d0b64dc3081b98a10ccd07ac9536f58f (diff) | |
download | gmp-95d98dfc07bd04667064b40aa9da72f5605e1cd8.tar.gz |
* mpz/cong.c, mpz/cong_2exp.c, mpz/cong_ui.c: New files.
Diffstat (limited to 'mpz/cong_2exp.c')
-rw-r--r-- | mpz/cong_2exp.c | 147 |
1 files changed, 147 insertions, 0 deletions
diff --git a/mpz/cong_2exp.c b/mpz/cong_2exp.c new file mode 100644 index 000000000..f0069b6b8 --- /dev/null +++ b/mpz/cong_2exp.c @@ -0,0 +1,147 @@ +/* mpz_congruent_2exp_p -- test congruence of mpz mod 2^n */ + +/* +Copyright 2001 Free Software Foundation, Inc. + +This file is part of the GNU MP Library. + +The GNU MP Library is free software; you can redistribute it and/or modify +it under the terms of the GNU Lesser General Public License as published by +the Free Software Foundation; either version 2.1 of the License, or (at your +option) any later version. + +The GNU MP Library is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY +or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public +License for more details. + +You should have received a copy of the GNU Lesser General Public License +along with the GNU MP Library; see the file COPYING.LIB. If not, write to +the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, +MA 02111-1307, USA. +*/ + +#include "gmp.h" +#include "gmp-impl.h" + + +int +mpz_congruent_2exp_p (mpz_srcptr a, mpz_srcptr c, unsigned long d) +{ + unsigned long i, dlimbs, dbits; + mp_ptr ap, cp; + mp_limb_t dmask, alimb, climb, sum; + int asize_signed, csize_signed, asize, csize; + + if (ABSIZ(a) < ABSIZ(c)) + MPZ_SRCPTR_SWAP (a, c); + + dlimbs = d / BITS_PER_MP_LIMB; + dbits = d % BITS_PER_MP_LIMB; + dmask = (CNST_LIMB(1) << dbits) - 1; + + ap = PTR(a); + cp = PTR(c); + + asize_signed = SIZ(a); + asize = ABS(asize_signed); + + csize_signed = SIZ(c); + csize = ABS(csize_signed); + + if (csize_signed == 0) + goto a_zeros; + + if ((asize_signed ^ csize_signed) >= 0) + { + /* same signs, direct comparison */ + + /* a==c for limbs in common */ + if (mpn_cmp (ap, cp, MIN (csize, dlimbs)) != 0) + return 0; + + /* if that's all of dlimbs, then a==c for remaining bits */ + if (csize > dlimbs) + return ((ap[dlimbs]-cp[dlimbs]) & dmask) == 0; + + a_zeros: + /* a remains, need all zero bits */ + + /* if d covers all of a and c, then must be exactly equal */ + if (asize <= dlimbs) + return asize == csize; + + /* whole limbs zero */ + for (i = csize; i < dlimbs; i++) + if (ap[i] != 0) + return 0; + + /* partial limb zero */ + return (ap[dlimbs] & dmask) == 0; + } + else + { + /* different signs, negated comparison */ + + /* common low zero limbs, stopping at first non-zeros, which must + match twos complement */ + i = 0; + for (;;) + { + ASSERT (i < csize); /* always have a non-zero limb on c */ + alimb = ap[i]; + climb = cp[i]; + sum = alimb + climb; + + if (i >= dlimbs) + return (sum & dmask) == 0; + i++; + + /* require both zero, or first non-zeros as twos-complements */ + if (sum != 0) + return 0; + + if (alimb != 0) + break; + } + + /* further limbs matching as ones-complement */ + for (;;) + { + if (i >= csize) + break; + + alimb = ap[i]; + climb = cp[i]; + sum = alimb + climb + 1; + + if (i >= dlimbs) + return (sum & dmask) == 0; + + if (sum != 0) + return 0; + + i++; + } + + /* no more c, so require all 1 bits in a */ + + if (asize < dlimbs) + return 0; /* not enough a */ + + /* whole limbs */ + for ( ; i < dlimbs; i++) + if (ap[i] + 1 != 0) + return 0; + + /* if only whole limbs, no further fetches from a */ + if (dbits == 0) + return 1; + + /* need enough a */ + if (asize == dlimbs) + return 0; + + return ((ap[dlimbs]+1) & dmask) == 0; + } +} |