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/* mpz_fdiv_r_2exp -- Divide a integer by 2**CNT and produce a remainder.
Copyright (C) 1991, 1993, 1994, 1995, 1998, 1999 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"
void
#if __STDC__
mpz_fdiv_r_2exp (mpz_ptr res, mpz_srcptr in, unsigned long int cnt)
#else
mpz_fdiv_r_2exp (res, in, cnt)
mpz_ptr res;
mpz_srcptr in;
unsigned long int cnt;
#endif
{
mp_size_t in_size = ABS (in->_mp_size);
mp_size_t res_size;
mp_size_t limb_cnt = cnt / BITS_PER_MP_LIMB;
mp_srcptr in_ptr = in->_mp_d;
if (in_size > limb_cnt)
{
/* The input operand is (probably) greater than 2**CNT. */
mp_limb_t x;
x = in_ptr[limb_cnt] & (((mp_limb_t) 1 << cnt % BITS_PER_MP_LIMB) - 1);
if (x != 0)
{
res_size = limb_cnt + 1;
if (res->_mp_alloc < res_size)
_mpz_realloc (res, res_size);
res->_mp_d[limb_cnt] = x;
}
else
{
res_size = limb_cnt;
MPN_NORMALIZE (in_ptr, res_size);
if (res->_mp_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, and may need
to round the result. */
res_size = in_size;
if (res->_mp_alloc < res_size)
_mpz_realloc (res, res_size);
limb_cnt = res_size;
}
if (res != in)
MPN_COPY (res->_mp_d, in->_mp_d, limb_cnt);
in_size = in->_mp_size;
res->_mp_size = res_size;
if (in_size < 0 && res_size != 0)
{
/* Result should be 2^CNT - RES */
mpz_t tmp;
MPZ_TMP_INIT (tmp, cnt/BITS_PER_MP_LIMB + 2);
mpz_set_ui (tmp, 1L);
mpz_mul_2exp (tmp, tmp, cnt);
mpz_sub (res, tmp, res);
}
}
/* This is an alternative ending of the above function using just low-level
functions. Tested, but perhaps excessive? */
#if 0
if (in->_mp_size < 0 && res_size != 0)
{
/* Result should be 2^CNT - RES */
mp_ptr rp;
limb_cnt = cnt / BITS_PER_MP_LIMB;
if (res->_mp_alloc <= limb_cnt)
_mpz_realloc (res, limb_cnt + 1);
rp = PTR(res);
if (res_size > limb_cnt)
{
mpn_nz_neg (rp, rp, res_size);
rp[limb_cnt] &= ~(~(mp_limb_t) 0 << cnt % BITS_PER_MP_LIMB);
MPN_NORMALIZE_NOT_ZERO (rp, res_size);
}
else
{
mp_size_t i;
mpn_nz_neg (rp, rp, res_size);
for (i = res_size; i < limb_cnt; i++)
rp[i] = ~ (mp_limb_t) 0;
res_size = limb_cnt;
if (cnt % BITS_PER_MP_LIMB != 0)
{
rp[res_size] = ((mp_limb_t) 1 << (cnt % BITS_PER_MP_LIMB)) - 1;
res_size++;
}
else
MPN_NORMALIZE_NOT_ZERO (rp, res_size);
}
}
SIZ(res) = res_size;
}
static void
mpn_nz_neg (rp, sp, n)
mp_ptr rp, sp;
mp_size_t n;
{
mp_size_t i;
mp_limb_t x;
x = sp[0];
rp[0] = -x;
for (i = 1; x == 0; i++)
{
x = sp[i];
rp[i] = -x;
}
for (; i < n; i++)
{
rp[i] = ~sp[i];
}
}
#endif
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