mirror of
https://github.com/vale981/arb
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47 lines
1 KiB
C
47 lines
1 KiB
C
/*
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Copyright (C) 2014 Fredrik Johansson
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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 it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version. See <http://www.gnu.org/licenses/>.
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*/
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#include "mag.h"
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void
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mag_exp_tail(mag_t z, const mag_t x, ulong N)
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{
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if (N == 0 || mag_is_inf(x))
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{
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mag_exp(z, x);
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}
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else if (mag_is_zero(x))
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{
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mag_zero(z);
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}
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else
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{
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mag_t t;
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mag_init(t);
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mag_set_ui_2exp_si(t, N, -1);
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/* bound by geometric series when N >= 2*x <=> N/2 >= x */
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if (mag_cmp(t, x) >= 0)
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{
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/* 2 c^N / N! */
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mag_pow_ui(t, x, N);
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mag_rfac_ui(z, N);
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mag_mul(z, z, t);
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mag_mul_2exp_si(z, z, 1);
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}
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else
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{
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mag_exp(z, x);
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}
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mag_clear(t);
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}
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}
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