efee5258bc
The MPFR library is a C library for multiple-precision floating-point computations with exact rounding (also called correct rounding). It is based on the GMP multiple-precision library and should replace the MPF class in further releases of GMP. GCC >= 4.2 requires MPFR.
144 lines
4.2 KiB
C
144 lines
4.2 KiB
C
/* mpfr_urandom (rop, state, rnd_mode) -- Generate a uniform pseudorandom
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real number between 0 and 1 (exclusive) and round it to the precision of rop
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according to the given rounding mode.
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Copyright 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
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Contributed by the Arenaire and Cacao projects, INRIA.
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This file is part of the GNU MPFR Library.
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The GNU MPFR 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 3 of the License, or (at your
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option) any later version.
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The GNU MPFR 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 MPFR Library; see the file COPYING.LESSER. If not, see
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http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
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#define MPFR_NEED_LONGLONG_H
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#include "mpfr-impl.h"
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static int
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random_rounding_bit (gmp_randstate_t rstate)
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{
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mp_limb_t r;
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mpfr_rand_raw (&r, rstate, 1);
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return r & MPFR_LIMB_ONE;
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}
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int
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mpfr_urandom (mpfr_ptr rop, gmp_randstate_t rstate, mpfr_rnd_t rnd_mode)
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{
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mpfr_limb_ptr rp;
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mpfr_prec_t nbits;
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mp_size_t nlimbs;
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mp_size_t n;
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mpfr_exp_t exp;
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mpfr_exp_t emin;
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int cnt;
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int inex;
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rp = MPFR_MANT (rop);
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nbits = MPFR_PREC (rop);
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nlimbs = MPFR_LIMB_SIZE (rop);
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MPFR_SET_POS (rop);
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exp = 0;
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emin = mpfr_get_emin ();
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if (MPFR_UNLIKELY (emin > 0))
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{
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if (rnd_mode == MPFR_RNDU || rnd_mode == MPFR_RNDA
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|| (emin == 1 && rnd_mode == MPFR_RNDN
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&& random_rounding_bit (rstate)))
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{
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mpfr_set_ui_2exp (rop, 1, emin - 1, rnd_mode);
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return +1;
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}
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else
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{
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MPFR_SET_ZERO (rop);
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return -1;
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}
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}
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/* Exponent */
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cnt = GMP_NUMB_BITS;
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while (cnt == GMP_NUMB_BITS)
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{
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/* generate one random limb rp[0] */
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mpfr_rand_raw (rp, rstate, GMP_NUMB_BITS);
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if (MPFR_UNLIKELY (rp[0] == 0))
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cnt = GMP_NUMB_BITS;
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else
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count_leading_zeros (cnt, rp[0]);
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if (MPFR_UNLIKELY (exp < emin + cnt))
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{
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/* To get here, we have been drawing more than -emin zeros
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in a row, then return 0 or the smallest representable
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positive number.
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The rounding to nearest mode is subtle:
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If exp - cnt == emin - 1, the rounding bit is set, except
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if cnt == GMP_NUMB_BITS in which case the rounding bit is
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outside rp[0] and must be generated. */
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if (rnd_mode == MPFR_RNDU || rnd_mode == MPFR_RNDA
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|| (rnd_mode == MPFR_RNDN && cnt == exp - emin - 1
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&& (cnt != GMP_NUMB_BITS || random_rounding_bit (rstate))))
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{
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mpfr_set_ui_2exp (rop, 1, emin - 1, rnd_mode);
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return +1;
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}
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else
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{
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MPFR_SET_ZERO (rop);
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return -1;
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}
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}
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exp -= cnt;
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}
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MPFR_EXP (rop) = exp; /* Warning: may be outside the current
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exponent range */
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/* Significand */
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mpfr_rand_raw (rp, rstate, nlimbs * GMP_NUMB_BITS);
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/* Set the msb to 1 since it was fixed by the exponent choice */
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rp[nlimbs - 1] |= MPFR_LIMB_HIGHBIT;
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/* If nbits isn't a multiple of GMP_NUMB_BITS, mask the low bits */
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n = nlimbs * GMP_NUMB_BITS - nbits;
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if (MPFR_LIKELY (n != 0))
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rp[0] &= ~MPFR_LIMB_MASK (n);
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/* Rounding */
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if (rnd_mode == MPFR_RNDU || rnd_mode == MPFR_RNDA
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|| (rnd_mode == MPFR_RNDN && random_rounding_bit (rstate)))
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{
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/* Take care of the exponent range: it may have been reduced */
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if (exp < emin)
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mpfr_set_ui_2exp (rop, 1, emin - 1, rnd_mode);
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else if (exp > mpfr_get_emax ())
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mpfr_set_inf (rop, +1); /* overflow, flag set by mpfr_check_range */
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else
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mpfr_nextabove (rop);
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inex = +1;
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}
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else
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inex = -1;
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return mpfr_check_range (rop, inex, rnd_mode);
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}
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