rrandomb.c
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上传日期:2022-08-06
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- /* mpz_rrandomb -- Generate a positive random mpz_t of specified bit size, with
- long runs of consecutive ones and zeros in the binary representation.
- Meant for testing of other MP routines.
- Copyright 2000, 2001, 2002, 2004 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- static void gmp_rrandomb __GMP_PROTO ((mp_ptr, gmp_randstate_t, mp_bitcnt_t));
- void
- mpz_rrandomb (mpz_ptr x, gmp_randstate_t rstate, mp_bitcnt_t nbits)
- {
- mp_size_t nl;
- nl = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS;
- if (nbits != 0)
- {
- MPZ_REALLOC (x, nl);
- gmp_rrandomb (PTR(x), rstate, nbits);
- }
- SIZ(x) = nl;
- }
- /* Ask _gmp_rand for 32 bits per call unless that's more than a limb can hold.
- Thus, we get the same random number sequence in the common cases.
- FIXME: We should always generate the same random number sequence! */
- #if GMP_NUMB_BITS < 32
- #define BITS_PER_RANDCALL GMP_NUMB_BITS
- #else
- #define BITS_PER_RANDCALL 32
- #endif
- static void
- gmp_rrandomb (mp_ptr rp, gmp_randstate_t rstate, mp_bitcnt_t nbits)
- {
- mp_bitcnt_t bi;
- mp_limb_t ranm; /* buffer for random bits */
- unsigned cap_chunksize, chunksize;
- mp_size_t i;
- /* Set entire result to 111..1 */
- i = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS - 1;
- rp[i] = GMP_NUMB_MAX >> (GMP_NUMB_BITS - (nbits % GMP_NUMB_BITS)) % GMP_NUMB_BITS;
- for (i = i - 1; i >= 0; i--)
- rp[i] = GMP_NUMB_MAX;
- _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
- cap_chunksize = nbits / (ranm % 4 + 1);
- cap_chunksize += cap_chunksize == 0; /* make it at least 1 */
- bi = nbits;
- for (;;)
- {
- _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
- chunksize = 1 + ranm % cap_chunksize;
- bi = (bi < chunksize) ? 0 : bi - chunksize;
- if (bi == 0)
- break; /* low chunk is ...1 */
- rp[bi / GMP_NUMB_BITS] ^= CNST_LIMB (1) << bi % GMP_NUMB_BITS;
- _gmp_rand (&ranm, rstate, BITS_PER_RANDCALL);
- chunksize = 1 + ranm % cap_chunksize;
- bi = (bi < chunksize) ? 0 : bi - chunksize;
- mpn_incr_u (rp + bi / GMP_NUMB_BITS, CNST_LIMB (1) << bi % GMP_NUMB_BITS);
- if (bi == 0)
- break; /* low chunk is ...0 */
- }
- }