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Diffstat (limited to 'mpz/kronzu.c')
-rw-r--r-- | mpz/kronzu.c | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/mpz/kronzu.c b/mpz/kronzu.c new file mode 100644 index 000000000..636afb36e --- /dev/null +++ b/mpz/kronzu.c @@ -0,0 +1,67 @@ +/* mpz_kronecker_zi_ui -- Kronecker/Jacobi symbol. */ + +/* +Copyright (C) 1999, 2000 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 Library General Public License as published by +the Free Software Foundation; either version 2 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 Library General Public +License for more details. + +You should have received a copy of the GNU Library 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" +#include "longlong.h" + + +/* This function is expected to be often used with b an odd prime, so the + code for odd b is nice and short. */ + +int +#if __STDC__ +mpz_kronecker_zi_ui (mpz_srcptr a, unsigned long b) +#else +mpz_kronecker_zi_ui (a, b) + mpz_srcptr a; + unsigned long b; +#endif +{ + int twos; + + ASSERT (sizeof (mp_limb_t) >= sizeof (unsigned long)); + + if (b & 1) + { + if (b != 1) + return mpn_jacobi_base (mpz_fdiv_ui (a, b), b, 0); + else + return 1; /* (a/1)=1 for any a */ + } + + if (b == 0) + return JACOBI_Z0 (a); + + /* (a/2)=0 if a even */ + if (mpz_even_p (a)) + return 0; + + /* (a/2)=(2/a) when a odd */ + count_trailing_zeros (twos, b); + if ((b >>= twos) == 1) + return JACOBI_TWOS_U (twos, PTR(a)[0]); + + return mpn_jacobi_base (mpz_fdiv_ui (a, b), b, + JACOBI_TWOS_U_BIT1(twos, PTR(a)[0])); +} |