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Annotation of OpenXM_contrib/gmp/mpz/urandomm.c, Revision 1.1

1.1     ! maekawa     1: /* mpz_urandomm (rop, state, n) -- Generate a uniform pseudorandom
        !             2:    integer in the range 0 to N-1, using STATE as the random state
        !             3:    previously initialized by a call to gmp_randinit().
        !             4:
        !             5: Copyright (C) 2000  Free Software Foundation, Inc.
        !             6:
        !             7: This file is part of the GNU MP Library.
        !             8:
        !             9: The GNU MP Library is free software; you can redistribute it and/or modify
        !            10: it under the terms of the GNU Lesser General Public License as published by
        !            11: the Free Software Foundation; either version 2.1 of the License, or (at your
        !            12: option) any later version.
        !            13:
        !            14: The GNU MP Library is distributed in the hope that it will be useful, but
        !            15: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            16: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
        !            17: License for more details.
        !            18:
        !            19: You should have received a copy of the GNU Lesser General Public License
        !            20: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            21: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            22: MA 02111-1307, USA. */
        !            23:
        !            24: #include "gmp.h"
        !            25: #include "gmp-impl.h"
        !            26: #include "longlong.h"
        !            27:
        !            28: void
        !            29: #if __STDC__
        !            30: mpz_urandomm (mpz_t rop, gmp_randstate_t rstate, mpz_t n)
        !            31: #else
        !            32: mpz_urandomm (rop, rstate, n)
        !            33:      mpz_t rop;
        !            34:      gmp_randstate_t rstate;
        !            35:      mpz_t n;
        !            36: #endif
        !            37: {
        !            38:   mpz_t t, p, m;
        !            39:   mp_ptr tp;
        !            40:   mp_size_t nbits, size;
        !            41:   int count;
        !            42:
        !            43:   /* FIXME: Should check for n == 0 and report error */
        !            44:
        !            45:   size = SIZ (n);
        !            46:   count_leading_zeros (count, PTR (n)[size - 1]);
        !            47:   nbits = size * BITS_PER_MP_LIMB - count;
        !            48:
        !            49:   /* Allocate enough for any mpz function called since a realloc of
        !            50:      these will fail.  */
        !            51:   MPZ_TMP_INIT (t, size);
        !            52:   MPZ_TMP_INIT (m, size + 1);
        !            53:   MPZ_TMP_INIT (p, size + 1);
        !            54:
        !            55:   /* Let m = highest possible random number plus 1.  */
        !            56:   mpz_set_ui (m, 0);
        !            57:   mpz_setbit (m, nbits);
        !            58:
        !            59:   /* Let p = floor(m / n) * n.  */
        !            60:   mpz_fdiv_q (p, m, n);
        !            61:   mpz_mul (p, p, n);
        !            62:
        !            63:   tp = PTR (t);
        !            64:   do
        !            65:     {
        !            66:       _gmp_rand (tp, rstate, nbits);
        !            67:       MPN_NORMALIZE (tp, size);        /* FIXME: Really necessary?  */
        !            68:       SIZ (t) = size;
        !            69:     }
        !            70:   while (mpz_cmp (t, p) >= 0);
        !            71:
        !            72:   mpz_mod (rop, t, n);
        !            73: }