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Annotation of OpenXM_contrib/gmp/mpn/generic/random2.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpn_random2 -- Generate random numbers with relatively long strings
                      2:    of ones and zeroes.  Suitable for border testing.
                      3:
                      4: Copyright (C) 1992, 1993, 1994, 1996 Free Software Foundation, Inc.
                      5:
                      6: This file is part of the GNU MP Library.
                      7:
                      8: The GNU MP Library is free software; you can redistribute it and/or modify
                      9: it under the terms of the GNU Library General Public License as published by
                     10: the Free Software Foundation; either version 2 of the License, or (at your
                     11: option) any later version.
                     12:
                     13: The GNU MP 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 Library General Public
                     16: License for more details.
                     17:
                     18: You should have received a copy of the GNU Library General Public License
                     19: along with the GNU MP 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:
                     26: #if defined (__hpux) || defined (alpha__)  || defined (__svr4__) || defined (__SVR4)
                     27: /* HPUX lacks random().  DEC OSF/1 1.2 random() returns a double.  */
                     28: long mrand48 ();
                     29: static inline long
                     30: random ()
                     31: {
                     32:   return mrand48 ();
                     33: }
                     34: #else
                     35: long random ();
                     36: #endif
                     37:
                     38: /* It's a bit tricky to get this right, so please test the code well
                     39:    if you hack with it.  Some early versions of the function produced
                     40:    random numbers with the leading limb == 0, and some versions never
                     41:    made the most significant bit set.  */
                     42:
                     43: void
                     44: mpn_random2 (res_ptr, size)
                     45:      mp_ptr res_ptr;
                     46:      mp_size_t size;
                     47: {
                     48:   int n_bits;
                     49:   int bit_pos;
                     50:   mp_size_t limb_pos;
                     51:   unsigned int ran;
                     52:   mp_limb_t limb;
                     53:
                     54:   limb = 0;
                     55:
                     56:   /* Start off in a random bit position in the most significant limb.  */
                     57:   bit_pos = random () & (BITS_PER_MP_LIMB - 1);
                     58:
                     59:   /* Least significant bit of RAN chooses string of ones/string of zeroes.
                     60:      Make most significant limb be non-zero by setting bit 0 of RAN.  */
                     61:   ran = random () | 1;
                     62:
                     63:   for (limb_pos = size - 1; limb_pos >= 0; )
                     64:     {
                     65:       n_bits = (ran >> 1) % BITS_PER_MP_LIMB + 1;
                     66:       if ((ran & 1) != 0)
                     67:        {
                     68:          /* Generate a string of ones.  */
                     69:          if (n_bits >= bit_pos)
                     70:            {
                     71:              res_ptr[limb_pos--] = limb | ((((mp_limb_t) 2) << bit_pos) - 1);
                     72:              bit_pos += BITS_PER_MP_LIMB;
                     73:              limb = (~(mp_limb_t) 0) << (bit_pos - n_bits);
                     74:            }
                     75:          else
                     76:            {
                     77:              limb |= ((((mp_limb_t) 1) << n_bits) - 1) << (bit_pos - n_bits + 1);
                     78:            }
                     79:        }
                     80:       else
                     81:        {
                     82:          /* Generate a string of zeroes.  */
                     83:          if (n_bits >= bit_pos)
                     84:            {
                     85:              res_ptr[limb_pos--] = limb;
                     86:              limb = 0;
                     87:              bit_pos += BITS_PER_MP_LIMB;
                     88:            }
                     89:        }
                     90:       bit_pos -= n_bits;
                     91:       ran = random ();
                     92:     }
                     93: }