mirror of
https://github.com/vale981/arb
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125 lines
3.5 KiB
C
125 lines
3.5 KiB
C
/*=============================================================================
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This file is part of ARB.
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ARB is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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ARB is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with ARB; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2012 Fredrik Johansson
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******************************************************************************/
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#include "fmprb.h"
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/*
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Returns a random rational in x. The binary denominator of x is multiplied
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by den_mult to select a base denominator to choose random integers
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between.
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The outcome is undefined if the midpoint or radius of x is non-finite,
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or if the exponent of the midpoint or radius is so large or small
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that representing the endpoints as exact rational numbers would
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cause overflows.
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*/
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void
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_fmprb_get_rand_fmpq(fmpz_t num, fmpz_t den, flint_rand_t state,
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const fmpz_t den_mult, const fmprb_t x)
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{
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fmpz_t a, b, exp;
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fmpz_init(a);
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fmpz_init(b);
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fmpz_init(exp);
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fmprb_get_interval_fmpz_2exp(a, b, exp, x);
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if (COEFF_IS_MPZ(*exp))
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{
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flint_printf("exception: fmprb_get_rand_fmpq: too large exponent\n");
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abort();
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}
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if (*exp >= 0)
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{
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fmpz_mul_2exp(a, a, *exp);
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fmpz_mul_2exp(b, b, *exp);
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}
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/* generate random integer in [a*den, b*den] */
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fmpz_mul(a, a, den_mult);
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fmpz_mul(b, b, den_mult);
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fmpz_add_ui(b, b, UWORD(1));
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fmpz_sub(b, b, a);
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/* return one endpoint with high probability (used for stress
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testing rounding) */
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if (n_randint(state, 6) == 0)
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{
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if (n_randint(state, 2))
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fmpz_zero(num);
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else
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fmpz_sub_ui(num, b, UWORD(1));
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}
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else
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{
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fmpz_randtest_mod(num, state, b);
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}
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fmpz_add(num, num, a);
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fmpz_set(den, den_mult);
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if (*exp < 0)
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fmpz_mul_2exp(den, den, -(*exp));
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fmpz_clear(a);
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fmpz_clear(b);
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fmpz_clear(exp);
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}
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/*
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Chooses a random rational number from the interval represented by x.
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A denominator is chosen by multiplying the binary denominator of x
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by a random integer up to size bits.
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The outcome is undefined if the midpoint or radius of x is non-finite,
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or if the exponent of the midpoint or radius is so large or small
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that representing the endpoints as exact rational numbers would
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cause overflows.
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*/
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void
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fmprb_get_rand_fmpq(fmpq_t q, flint_rand_t state, const fmprb_t x, slong bits)
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{
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/* there is only one rational */
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if (fmprb_is_exact(x))
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{
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fmpr_get_fmpq(q, fmprb_midref(x));
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return;
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}
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/* pick a denominator */
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fmpz_randbits(fmpq_denref(q), state, n_randint(state, bits + 1));
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fmpz_abs(fmpq_denref(q), fmpq_denref(q));
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if (fmpz_is_zero(fmpq_denref(q)))
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fmpz_one(fmpq_denref(q));
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_fmprb_get_rand_fmpq(fmpq_numref(q), fmpq_denref(q), state, fmpq_denref(q), x);
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fmpq_canonicalise(q);
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}
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