93 lines
2.6 KiB
C
93 lines
2.6 KiB
C
/* mpz_urandomm (rop, state, n) -- Generate a uniform pseudorandom
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integer in the range 0 to N-1, using STATE as the random state
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previously initialized by a call to gmp_randinit().
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Copyright 2000, 2002 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP 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 by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP 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 GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include "mpir.h"
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#include "gmp-impl.h"
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#include "longlong.h" /* for count_leading_zeros */
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#define MAX_URANDOMM_ITER 80
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void
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mpz_urandomm (mpz_ptr rop, gmp_randstate_t rstate, mpz_srcptr n)
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{
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mp_ptr rp, np, nlast;
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mp_size_t nbits, size;
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int count;
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int pow2;
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int cmp;
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int overlap=0;
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size = ABSIZ (n);
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if (size == 0)
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DIVIDE_BY_ZERO;
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nlast = &PTR (n)[size - 1];
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/* Detect whether n is a power of 2. */
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pow2 = POW2_P (*nlast);
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if (pow2 != 0)
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for (np = PTR (n); np < nlast; np++)
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if (*np != 0)
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{
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pow2 = 0; /* Mark n as `not a power of two'. */
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break;
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}
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count_leading_zeros (count, *nlast);
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nbits = size * GMP_NUMB_BITS - (count - GMP_NAIL_BITS) - pow2;
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if (nbits == 0) /* nbits == 0 means that n was == 1. */
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{
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SIZ (rop) = 0;
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return;
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}
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np=PTR(n);
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rp=PTR(rop);
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if(np==rp)
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{overlap=1;
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np=__GMP_ALLOCATE_FUNC_LIMBS(size);
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MPN_COPY(np,PTR(n),size);
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}
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/* Here the allocated size can be one too much if n is a power of
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(2^GMP_NUMB_BITS) but it's convenient for using mpn_cmp below. */
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rp = MPZ_REALLOC (rop, size);
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/* Clear last limb to prevent the case in which size is one too much. */
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rp[size - 1] = 0;
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count = MAX_URANDOMM_ITER; /* Set iteration count limit. */
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do
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{
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_gmp_rand (rp, rstate, nbits);
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MPN_CMP (cmp, rp, np, size);
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}
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while (cmp >= 0 && --count != 0);
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if (count == 0)
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/* Too many iterations; return result mod n == result - n */
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mpn_sub_n (rp, rp, np, size);
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if(overlap)__GMP_FREE_FUNC_LIMBS(np,size);
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MPN_NORMALIZE (rp, size);
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SIZ (rop) = size;
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}
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