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Annotation of OpenXM_contrib/gmp/mpfr/ui_pow_ui.c, Revision 1.1

1.1     ! ohara       1: /*  mpfr_ui_pow_ui -- compute the power beetween two machine integer
        !             2:
        !             3: Copyright 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
        !             4:
        !             5: This file is part of the MPFR Library.
        !             6:
        !             7: The MPFR 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 2.1 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The MPFR 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 MPFR Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include "gmp.h"
        !            23: #include "mpfr.h"
        !            24: #include "mpfr-impl.h"
        !            25:
        !            26: int
        !            27: mpfr_ui_pow_ui (mpfr_ptr x, unsigned long int y, unsigned long int n,
        !            28:                 mp_rnd_t rnd)
        !            29: {
        !            30:   long int err;
        !            31:   unsigned long m;
        !            32:   mpfr_t res;
        !            33:   mp_prec_t prec;
        !            34:   int inexact;
        !            35:
        !            36:   MPFR_CLEAR_FLAGS(x);
        !            37:
        !            38:   if (n == 0) /* y^0 = 1 for any y */
        !            39:     return mpfr_set_ui (x, 1, rnd);
        !            40:
        !            41:   if (y == 0) /* 0^n = 0 for any n > 0 */
        !            42:     return mpfr_set_ui (x, 0, rnd);
        !            43:
        !            44:   mpfr_save_emin_emax ();
        !            45:   mpfr_init (res);
        !            46:
        !            47:   prec = MPFR_PREC(x);
        !            48:
        !            49:   do
        !            50:     {
        !            51:       int i;
        !            52:
        !            53:       prec += 3;
        !            54:       for (i = 0, m = n; m; i++, m >>= 1)
        !            55:         prec++;
        !            56:       mpfr_set_prec (res, prec);
        !            57:       inexact = mpfr_set_ui (res, y, GMP_RNDU);
        !            58:       err = 1;
        !            59:       /* now 2^(i-1) <= n < 2^i */
        !            60:       for (i-=2; i>=0; i--)
        !            61:        {
        !            62:          if (mpfr_mul (res, res, res, GMP_RNDU))
        !            63:            inexact = 1;
        !            64:          err++;
        !            65:          if (n & (1 << i))
        !            66:            if (mpfr_mul_ui (res, res, y, GMP_RNDU))
        !            67:              inexact = 1;
        !            68:        }
        !            69:       err = prec - err;
        !            70:       if (err < 0)
        !            71:        err = 0;
        !            72:     }
        !            73:   while (inexact && (mpfr_can_round (res, err,
        !            74:           MPFR_SIGN(res) > 0 ? GMP_RNDU : GMP_RNDD, rnd, MPFR_PREC(x)) == 0));
        !            75:
        !            76:   if (mpfr_set (x, res, rnd))
        !            77:     inexact = 1;
        !            78:
        !            79:   mpfr_clear (res);
        !            80:
        !            81:   MPFR_RESTORE_RET(inexact, x, rnd);
        !            82: }