101 lines
3.1 KiB
C
101 lines
3.1 KiB
C
/* mpn_rrandom -- Generate random numbers with relatively long strings
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of ones and zeroes. Suitable for border testing.
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Copyright 1992, 1993, 1994, 1996, 2000, 2001, 2002, 2004 Free Software
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Foundation, Inc.
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Copyright 2009 Jason Moxham
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This file is part of the MPIR Library.
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The MPIR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation; either version 2.1 of the License, or (at
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your option) any later version.
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The MPIR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the MPIR Library; see the file COPYING.LIB. If not, write
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to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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Boston, MA 02110-1301, USA.
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*/
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#include "mpir.h"
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#include "gmp-impl.h"
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static void gmp_rrandomb _PROTO ((mp_ptr rp, gmp_randstate_t rstate, gmp_ui nbits));
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/* Ask _gmp_rand for 32 bits per call unless that's more than a limb can hold.
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Thus, we get the same random number sequence in the common cases.
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FIXME: We should always generate the same random number sequence! */
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#if GMP_NUMB_BITS < 32
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#define BITS_PER_RANDCALL GMP_NUMB_BITS
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#else
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#define BITS_PER_RANDCALL 32
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#endif
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void
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mpn_rrandom (mp_ptr rp, gmp_randstate_t rnd, mp_size_t n)
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{
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int bit_pos; /* bit number of least significant bit where
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next bit field to be inserted */
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mp_limb_t ran, ranm; /* buffer for random bits */
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/* FIXME: Is n==0 supposed to be allowed? */
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ASSERT (n >= 0);
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_gmp_rand (&ranm, rnd, BITS_PER_RANDCALL);
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ran = ranm;
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/* Start off at a random bit position in the most significant limb. */
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bit_pos = ran % GMP_NUMB_BITS;
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gmp_rrandomb (rp, rnd, n * GMP_NUMB_BITS - bit_pos);
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}
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static void
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gmp_rrandomb (mp_ptr rp, gmp_randstate_t rstate, gmp_ui nbits)
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{
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gmp_ui bi;
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mp_limb_t ranm; /* buffer for random bits */
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unsigned cap_chunksize, chunksize;
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mp_size_t i;
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/* Set entire result to 111..1 */
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i = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS - 1;
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rp[i] = GMP_NUMB_MAX >> (GMP_NUMB_BITS - (nbits % GMP_NUMB_BITS)) % GMP_NUMB_BITS;
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for (i = i - 1; i >= 0; i--)
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rp[i] = GMP_NUMB_MAX;
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_gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
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cap_chunksize = nbits / (ranm % 4 + 1);
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cap_chunksize += cap_chunksize == 0; /* make it at least 1 */
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bi = nbits;
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for (;;)
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{
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_gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
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chunksize = 1 + ranm % cap_chunksize;
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bi = (bi < chunksize) ? 0 : bi - chunksize;
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if (bi == 0)
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break; /* low chunk is ...1 */
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rp[bi / GMP_NUMB_BITS] ^= CNST_LIMB (1) << bi % GMP_NUMB_BITS;
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_gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
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chunksize = 1 + ranm % cap_chunksize;
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bi = (bi < chunksize) ? 0 : bi - chunksize;
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mpn_incr_u (rp + bi / GMP_NUMB_BITS, CNST_LIMB (1) << bi % GMP_NUMB_BITS);
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if (bi == 0)
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break; /* low chunk is ...0 */
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}
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}
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