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Annotation of OpenXM_contrib/gmp/mpfr/get_z_exp.c, Revision 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: }