source/libs/mpfr/mpfr-3.1.3/src/get_sj.c

   1 /* mpfr_get_sj -- convert a MPFR number to a huge machine signed integer
   2
   3 Copyright 2004, 2006-2015 Free Software Foundation, Inc.
   4 Contributed by the AriC and Caramel projects, INRIA.
   5
   6 This file is part of the GNU MPFR Library.
   7
   8 The GNU MPFR Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MPFR Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MPFR Library; see the file COPYING.LESSER.  If not, see
  20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
  21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
  22
  23 #ifdef HAVE_CONFIG_H
  24 # include "config.h"            /* for a build within gmp */
  25 #endif
  26
  27 #include "mpfr-intmax.h"
  28 #include "mpfr-impl.h"
  29
  30 #ifdef _MPFR_H_HAVE_INTMAX_T
  31
  32 intmax_t
  33 mpfr_get_sj (mpfr_srcptr f, mpfr_rnd_t rnd)
  34 {
  35   intmax_t r;
  36   mpfr_prec_t prec;
  37   mpfr_t x;
  38
  39   if (MPFR_UNLIKELY (!mpfr_fits_intmax_p (f, rnd)))
  40     {
  41       MPFR_SET_ERANGE ();
  42       return MPFR_IS_NAN (f) ? 0 :
  43         MPFR_IS_NEG (f) ? MPFR_INTMAX_MIN : MPFR_INTMAX_MAX;
  44     }
  45
  46   if (MPFR_IS_ZERO (f))
  47      return (intmax_t) 0;
  48
  49   /* determine the precision of intmax_t */
  50   for (r = MPFR_INTMAX_MIN, prec = 0; r != 0; r /= 2, prec++)
  51     { }
  52   /* Note: though INTMAX_MAX would have been sufficient for the conversion,
  53      we chose INTMAX_MIN so that INTMAX_MIN - 1 is always representable in
  54      precision prec; this is useful to detect overflows in MPFR_RNDZ (will
  55      be needed later). */
  56
  57   /* Now, r = 0. */
  58
  59   mpfr_init2 (x, prec);
  60   mpfr_rint (x, f, rnd);
  61   MPFR_ASSERTN (MPFR_IS_FP (x));
  62
  63   if (MPFR_NOTZERO (x))
  64     {
  65       mp_limb_t *xp;
  66       int sh, n;        /* An int should be sufficient in this context. */
  67
  68       xp = MPFR_MANT (x);
  69       sh = MPFR_GET_EXP (x);
  70       MPFR_ASSERTN ((mpfr_prec_t) sh <= prec);
  71       if (MPFR_INTMAX_MIN + MPFR_INTMAX_MAX != 0
  72           && MPFR_UNLIKELY ((mpfr_prec_t) sh == prec))
  73         {
  74           /* 2's complement and x <= INTMAX_MIN: in the case mp_limb_t
  75              has the same size as intmax_t, we cannot use the code in
  76              the for loop since the operations would be performed in
  77              unsigned arithmetic. */
  78           MPFR_ASSERTN (MPFR_IS_NEG (x) && (mpfr_powerof2_raw (x)));
  79           r = MPFR_INTMAX_MIN;
  80         }
  81       else if (MPFR_IS_POS (x))
  82         {
  83           /* Note: testing the condition sh >= 0 is necessary to avoid
  84              an undefined behavior on xp[n] >> S when S >= GMP_NUMB_BITS
  85              (even though xp[n] == 0 in such a case). This can happen if
  86              sizeof(mp_limb_t) < sizeof(intmax_t) and |x| is small enough
  87              because of the trailing bits due to its normalization. */
  88           for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--)
  89             {
  90               sh -= GMP_NUMB_BITS;
  91               /* Note the concerning the casts below:
  92                  When sh >= 0, the cast must be performed before the shift
  93                  for the case sizeof(intmax_t) > sizeof(mp_limb_t).
  94                  When sh < 0, the cast must be performed after the shift
  95                  for the case sizeof(intmax_t) == sizeof(mp_limb_t), as
  96                  mp_limb_t is unsigned, therefore not representable as an
  97                  intmax_t when the MSB is 1 (this is the case here). */
  98               MPFR_ASSERTD (sh < GMP_NUMB_BITS && -sh < GMP_NUMB_BITS);
  99               r += (sh >= 0
 100                     ? (intmax_t) xp[n] << sh
 101                     : (intmax_t) (xp[n] >> (-sh)));
 102             }
 103         }
 104       else
 105         {
 106           /* See the comments for the case x positive. */
 107           for (n = MPFR_LIMB_SIZE (x) - 1; n >= 0 && sh >= 0; n--)
 108             {
 109               sh -= GMP_NUMB_BITS;
 110               MPFR_ASSERTD (sh < GMP_NUMB_BITS && -sh < GMP_NUMB_BITS);
 111               r -= (sh >= 0
 112                     ? (intmax_t) xp[n] << sh
 113                     : (intmax_t) (xp[n] >> (-sh)));
 114             }
 115         }
 116     }
 117
 118   mpfr_clear (x);
 119
 120   return r;
 121 }
 122
 123 #endif