get_si.c

/* mpf_get_si -- mpf to long conversion

Copyright 2001, 2002, 2004 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 Lesser General Public License as published by
the Free Software Foundation; either version 3 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 Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */

#include "gmp.h"
#include "gmp-impl.h"


/* Any fraction bits are truncated, meaning simply discarded.

   For values bigger than a long, the low bits are returned, like
   mpz_get_si, but this isn't documented.

   Notice this is equivalent to mpz_set_f + mpz_get_si.


   Implementation:

   fl is established in basically the same way as for mpf_get_ui, see that
   code for explanations of the conditions.

   However unlike mpf_get_ui we need an explicit return 0 for exp<=0.  When
   f is a negative fraction (ie. size<0 and exp<=0) we can't let fl==0 go
   through to the zany final "~ ((fl - 1) & LONG_MAX)", that would give
   -0x80000000 instead of the desired 0.  */

long
mpf_get_si (mpf_srcptr f)
{
  mp_exp_t exp;
  mp_size_t size, abs_size;
  mp_srcptr fp;
  mp_limb_t fl;

  exp = EXP (f);
  size = SIZ (f);
  fp = PTR (f);

  /* fraction alone truncates to zero
     this also covers zero, since we have exp==0 for zero */
  if (exp <= 0)
    return 0L;

  /* there are some limbs above the radix point */

  fl = 0;
  abs_size = ABS (size);
  if (abs_size >= exp)
    fl = fp[abs_size-exp];

#if BITS_PER_ULONG > GMP_NUMB_BITS
  if (exp > 1 && abs_size+1 >= exp)
    fl |= fp[abs_size - exp + 1] << GMP_NUMB_BITS;
#endif

  if (size > 0)
    return fl & LONG_MAX;
  else
    /* this form necessary to correctly handle -0x80..00 */
    return ~ ((fl - 1) & LONG_MAX);
}