diff options
Diffstat (limited to 'gnu/lib/libgmp/mpz_mod_2exp.c')
-rw-r--r-- | gnu/lib/libgmp/mpz_mod_2exp.c | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/gnu/lib/libgmp/mpz_mod_2exp.c b/gnu/lib/libgmp/mpz_mod_2exp.c new file mode 100644 index 0000000..696acd4 --- /dev/null +++ b/gnu/lib/libgmp/mpz_mod_2exp.c @@ -0,0 +1,82 @@ +/* mpz_mod_2exp -- divide a MP_INT by 2**n and produce a remainder. + +Copyright (C) 1991 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 General Public License as published by +the Free Software Foundation; either version 2, 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 General Public License for more details. + +You should have received a copy of the GNU General Public License +along with the GNU MP Library; see the file COPYING. If not, write to +the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" + +void +#ifdef __STDC__ +mpz_mod_2exp (MP_INT *res, const MP_INT *in, unsigned long int cnt) +#else +mpz_mod_2exp (res, in, cnt) + MP_INT *res; + const MP_INT *in; + unsigned long int cnt; +#endif +{ + mp_size in_size = ABS (in->size); + mp_size res_size; + mp_size limb_cnt = cnt / BITS_PER_MP_LIMB; + mp_srcptr in_ptr = in->d; + + if (in_size > limb_cnt) + { + /* The input operand is (probably) greater than 2**CNT. */ + mp_limb x; + + x = in_ptr[limb_cnt] & (((mp_limb) 1 << cnt % BITS_PER_MP_LIMB) - 1); + if (x != 0) + { + res_size = limb_cnt + 1; + if (res->alloc < res_size) + _mpz_realloc (res, res_size); + + res->d[limb_cnt] = x; + } + else + { + mp_size i; + + for (i = limb_cnt - 1; i >= 0; i--) + if (in_ptr[i] != 0) + break; + res_size = i + 1; + + if (res->alloc < res_size) + _mpz_realloc (res, res_size); + + limb_cnt = res_size; + } + } + else + { + /* The input operand is smaller than 2**CNT. We perform a no-op, + apart from that we might need to copy IN to RES. */ + res_size = in_size; + if (res->alloc < res_size) + _mpz_realloc (res, res_size); + + limb_cnt = res_size; + } + + if (res != in) + MPN_COPY (res->d, in->d, limb_cnt); + res->size = (in->size >= 0) ? res_size : -res_size; +} |