contrib/gmp/mpf/get_si.c

   1 /* mpf_get_si -- mpf to long conversion
   2
   3 Copyright 2001, 2002, 2004 Free Software Foundation, Inc.
   4
   5 This file is part of the GNU MP Library.
   6
   7 The GNU MP Library is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU Lesser General Public License as published by
   9 the Free Software Foundation; either version 3 of the License, or (at your
  10 option) any later version.
  11
  12 The GNU MP Library is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15 License for more details.
  16
  17 You should have received a copy of the GNU Lesser General Public License
  18 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  19
  20 #include "gmp.h"
  21 #include "gmp-impl.h"
  22
  23
  24 /* Any fraction bits are truncated, meaning simply discarded.
  25
  26    For values bigger than a long, the low bits are returned, like
  27    mpz_get_si, but this isn't documented.
  28
  29    Notice this is equivalent to mpz_set_f + mpz_get_si.
  30
  31
  32    Implementation:
  33
  34    fl is established in basically the same way as for mpf_get_ui, see that
  35    code for explanations of the conditions.
  36
  37    However unlike mpf_get_ui we need an explicit return 0 for exp<=0.  When
  38    f is a negative fraction (ie. size<0 and exp<=0) we can't let fl==0 go
  39    through to the zany final "~ ((fl - 1) & LONG_MAX)", that would give
  40    -0x80000000 instead of the desired 0.  */
  41
  42 long
  43 mpf_get_si (mpf_srcptr f) __GMP_NOTHROW
  44 {
  45   mp_exp_t exp;
  46   mp_size_t size, abs_size;
  47   mp_srcptr fp;
  48   mp_limb_t fl;
  49
  50   exp = EXP (f);
  51   size = SIZ (f);
  52   fp = PTR (f);
  53
  54   /* fraction alone truncates to zero
  55      this also covers zero, since we have exp==0 for zero */
  56   if (exp <= 0)
  57     return 0L;
  58
  59   /* there are some limbs above the radix point */
  60
  61   fl = 0;
  62   abs_size = ABS (size);
  63   if (abs_size >= exp)
  64     fl = fp[abs_size-exp];
  65
  66 #if BITS_PER_ULONG > GMP_NUMB_BITS
  67   if (exp > 1 && abs_size+1 >= exp)
  68     fl |= fp[abs_size - exp + 1] << GMP_NUMB_BITS;
  69 #endif
  70
  71   if (size > 0)
  72     return fl & LONG_MAX;
  73   else
  74     /* this form necessary to correctly handle -0x80..00 */
  75     return -1 - (long) ((fl - 1) & LONG_MAX);
  76 }