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Annotation of OpenXM_contrib/gmp/mpfr/get_z_exp.c, Revision 1.1.1.1

1.1       ohara       1: /* mpfr_get_z_exp -- get a multiple-precision integer and an exponent
                      2:                      from a floating-point number
                      3:
                      4: Copyright 2000, 2001, 2002 Free Software Foundation, Inc.
                      5:
                      6: This file is part of the MPFR Library.
                      7:
                      8: The 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 2.1 of the License, or (at your
                     11: option) any later version.
                     12:
                     13: The 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 MPFR Library; see the file COPYING.LIB.  If not, write to
                     20: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     21: MA 02111-1307, USA. */
                     22:
                     23: #include "gmp.h"
                     24: #include "gmp-impl.h"
                     25: #include "longlong.h"
                     26: #include "mpfr.h"
                     27: #include "mpfr-impl.h"
                     28:
                     29: /* puts the mantissa of f into z, and returns 'exp' such that f = z * 2^exp
                     30:  *
                     31:  * 0 doesn't have an exponent, therefore the returned exponent in this case
                     32:  * isn't really important. We choose to return __mpfr_emin because
                     33:  *   1) it is in the exponent range [__mpfr_emin,__mpfr_emax],
                     34:  *   2) the smaller a number is (in absolute value), the smaller its
                     35:  *      exponent is. In other words, the f -> exp function is monotonous
                     36:  *      on nonnegative numbers.
                     37:  * Note that this is different from the C function frexp().
                     38:  */
                     39:
                     40: mp_exp_t
                     41: mpfr_get_z_exp (mpz_ptr z, mpfr_srcptr f)
                     42: {
                     43:   mp_size_t fn;
                     44:   int sh;
                     45:
                     46:   MPFR_ASSERTN(MPFR_IS_FP(f));
                     47:
                     48:   if (MPFR_IS_ZERO(f))
                     49:     {
                     50:       mpz_set_ui (z, 0);
                     51:       return __mpfr_emin;
                     52:     }
                     53:
                     54:   fn = 1 + (MPFR_PREC(f) - 1) / BITS_PER_MP_LIMB;
                     55:
                     56:   /* check whether allocated space for z is enough */
                     57:   if (ALLOC(z) < fn)
                     58:     MPZ_REALLOC(z, fn);
                     59:
                     60:   sh = (mp_prec_t) fn * BITS_PER_MP_LIMB - MPFR_PREC(f);
                     61:   if (sh)
                     62:     mpn_rshift (PTR(z), MPFR_MANT(f), fn, sh);
                     63:   else
                     64:     MPN_COPY (PTR(z), MPFR_MANT(f), fn);
                     65:
                     66:   SIZ(z) = fn;
                     67:
                     68:   MPFR_ASSERTN((mp_exp_unsigned_t) MPFR_EXP(f) - MPFR_EMIN_MIN
                     69:                >= (mp_exp_unsigned_t) MPFR_PREC(f));
                     70:   return MPFR_EXP(f) - MPFR_PREC(f);
                     71: }