diff options
Diffstat (limited to 'vendor/gmp-6.3.0/mpz/divegcd.c')
| -rw-r--r-- | vendor/gmp-6.3.0/mpz/divegcd.c | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/vendor/gmp-6.3.0/mpz/divegcd.c b/vendor/gmp-6.3.0/mpz/divegcd.c new file mode 100644 index 0000000..dc236c3 --- /dev/null +++ b/vendor/gmp-6.3.0/mpz/divegcd.c @@ -0,0 +1,156 @@ +/* mpz_divexact_gcd -- exact division optimized for GCDs. + + THE FUNCTIONS IN THIS FILE ARE FOR INTERNAL USE AND ARE ALMOST CERTAIN TO + BE SUBJECT TO INCOMPATIBLE CHANGES IN FUTURE GNU MP RELEASES. + +Copyright 2000, 2005, 2011, 2012 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 either: + + * the GNU Lesser General Public License as published by the Free + Software Foundation; either version 3 of the License, or (at your + option) any later version. + +or + + * the GNU General Public License as published by the Free Software + Foundation; either version 2 of the License, or (at your option) any + later version. + +or both in parallel, as here. + +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 General Public License +for more details. + +You should have received copies of the GNU General Public License and the +GNU Lesser General Public License along with the GNU MP Library. If not, +see https://www.gnu.org/licenses/. */ + +#include "gmp-impl.h" +#include "longlong.h" + + +/* Set q to a/d, expecting d to be from a GCD and therefore usually small. + + The distribution of GCDs of random numbers can be found in Knuth volume 2 + section 4.5.2 theorem D. + + GCD chance + 1 60.8% + 2^k 20.2% (1<=k<32) + 3*2^k 9.0% (1<=k<32) + other 10.1% + + Only the low limb is examined for optimizations, since GCDs bigger than + 2^32 (or 2^64) will occur very infrequently. + + Future: This could change to an mpn_divexact_gcd, possibly partly + inlined, if/when the relevant mpq functions change to an mpn based + implementation. */ + + +#if GMP_NUMB_BITS % 2 == 0 +static void +mpz_divexact_by3 (mpz_ptr q, mpz_srcptr a) +{ + mp_size_t size = SIZ(a); + mp_size_t abs_size = ABS(size); + mp_ptr qp; + + qp = MPZ_REALLOC (q, abs_size); + + mpn_bdiv_dbm1 (qp, PTR(a), abs_size, GMP_NUMB_MASK / 3); + + abs_size -= (qp[abs_size-1] == 0); + SIZ(q) = (size>0 ? abs_size : -abs_size); +} +#endif + +#if GMP_NUMB_BITS % 4 == 0 +static void +mpz_divexact_by5 (mpz_ptr q, mpz_srcptr a) +{ + mp_size_t size = SIZ(a); + mp_size_t abs_size = ABS(size); + mp_ptr qp; + + qp = MPZ_REALLOC (q, abs_size); + + mpn_bdiv_dbm1 (qp, PTR(a), abs_size, GMP_NUMB_MASK / 5); + + abs_size -= (qp[abs_size-1] == 0); + SIZ(q) = (size>0 ? abs_size : -abs_size); +} +#endif + +static void +mpz_divexact_limb (mpz_ptr q, mpz_srcptr a, mp_limb_t d) +{ + mp_size_t size = SIZ(a); + mp_size_t abs_size = ABS(size); + mp_ptr qp; + + qp = MPZ_REALLOC (q, abs_size); + + MPN_DIVREM_OR_DIVEXACT_1 (qp, PTR(a), abs_size, d); + + abs_size -= (qp[abs_size-1] == 0); + SIZ(q) = (size > 0 ? abs_size : -abs_size); +} + +void +mpz_divexact_gcd (mpz_ptr q, mpz_srcptr a, mpz_srcptr d) +{ + ASSERT (mpz_sgn (d) > 0); + + if (SIZ(a) == 0) + { + SIZ(q) = 0; + return; + } + + if (SIZ(d) == 1) + { + mp_limb_t dl = PTR(d)[0]; + int twos; + + if ((dl & 1) == 0) + { + count_trailing_zeros (twos, dl); + dl >>= twos; + mpz_tdiv_q_2exp (q, a, twos); + a = q; + } + + if (dl == 1) + { + if (q != a) + mpz_set (q, a); + return; + } +#if GMP_NUMB_BITS % 2 == 0 + if (dl == 3) + { + mpz_divexact_by3 (q, a); + return; + } +#endif +#if GMP_NUMB_BITS % 4 == 0 + if (dl == 5) + { + mpz_divexact_by5 (q, a); + return; + } +#endif + + mpz_divexact_limb (q, a, dl); + return; + } + + mpz_divexact (q, a, d); +} |