source/libs/gmp/gmp-src/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 either:
   9
  10   * the GNU Lesser General Public License as published by the Free
  11     Software Foundation; either version 3 of the License, or (at your
  12     option) any later version.
  13
  14 or
  15
  16   * the GNU General Public License as published by the Free Software
  17     Foundation; either version 2 of the License, or (at your option) any
  18     later version.
  19
  20 or both in parallel, as here.
  21
  22 The GNU MP Library is distributed in the hope that it will be useful, but
  23 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  24 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  25 for more details.
  26
  27 You should have received copies of the GNU General Public License and the
  28 GNU Lesser General Public License along with the GNU MP Library.  If not,
  29 see https://www.gnu.org/licenses/.  */
  30
  31 #include "gmp.h"
  32 #include "gmp-impl.h"
  33
  34
  35 /* Any fraction bits are truncated, meaning simply discarded.
  36
  37    For values bigger than a long, the low bits are returned, like
  38    mpz_get_si, but this isn't documented.
  39
  40    Notice this is equivalent to mpz_set_f + mpz_get_si.
  41
  42
  43    Implementation:
  44
  45    fl is established in basically the same way as for mpf_get_ui, see that
  46    code for explanations of the conditions.
  47
  48    However unlike mpf_get_ui we need an explicit return 0 for exp<=0.  When
  49    f is a negative fraction (ie. size<0 and exp<=0) we can't let fl==0 go
  50    through to the zany final "~ ((fl - 1) & LONG_MAX)", that would give
  51    -0x80000000 instead of the desired 0.  */
  52
  53 long
  54 mpf_get_si (mpf_srcptr f) __GMP_NOTHROW
  55 {
  56   mp_exp_t exp;
  57   mp_size_t size, abs_size;
  58   mp_srcptr fp;
  59   mp_limb_t fl;
  60
  61   exp = EXP (f);
  62   size = SIZ (f);
  63   fp = PTR (f);
  64
  65   /* fraction alone truncates to zero
  66      this also covers zero, since we have exp==0 for zero */
  67   if (exp <= 0)
  68     return 0L;
  69
  70   /* there are some limbs above the radix point */
  71
  72   fl = 0;
  73   abs_size = ABS (size);
  74   if (abs_size >= exp)
  75     fl = fp[abs_size-exp];
  76
  77 #if BITS_PER_ULONG > GMP_NUMB_BITS
  78   if (exp > 1 && abs_size+1 >= exp)
  79     fl |= fp[abs_size - exp + 1] << GMP_NUMB_BITS;
  80 #endif
  81
  82   if (size > 0)
  83     return fl & LONG_MAX;
  84   else
  85     /* this form necessary to correctly handle -0x80..00 */
  86     return -1 - (long) ((fl - 1) & LONG_MAX);
  87 }