/* mpn_divexact_by exact division by (B-1)/f Copyright 2009 Jason Moxham This file is part of the MPIR Library. The MPIR 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 MPIR 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 MPIR Library; see the file COPYING.LIB. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ #include "mpir.h" #include "gmp-impl.h" #include "longlong.h" /* (xp, n) = (qp, n)*f - ret*B^n and 0 <= ret < f Note the divexact_by3 code is just a special case of this */ mp_limb_t mpn_divexact_byfobm1(mp_ptr qp, mp_srcptr xp, mp_size_t n, mp_limb_t f, mp_limb_t Bm1of) { mp_size_t j; mp_limb_t c, acc, ax, dx; ASSERT(n > 0); ASSERT_MPN(xp, n); ASSERT(MPN_SAME_OR_SEPARATE_P(qp, xp, n)); ASSERT(Bm1of*f + 1 == 0); acc = 0*Bm1of; /* carry in is 0 */ for (j = 0; j <= n - 1; j++) { umul_ppmm(dx, ax, xp[j], Bm1of); SUBC_LIMB(c, acc, acc, ax); qp[j] = acc; acc -= dx + c; } /* return next quotient*(-f) */ return acc*(-f); }