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4c74403188
Change-Id: Iae65e95cfa0d92091b8b0a424ae36d88efa76aa9 Reviewed-on: https://review.haiku-os.org/c/buildtools/+/3020 Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
84 lines
2.2 KiB
C
84 lines
2.2 KiB
C
/* mpf_pow_ui -- Compute b^e.
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Copyright 1998, 1999, 2001, 2012, 2015 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 either:
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* the GNU Lesser General Public License as published by the Free
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Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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or
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* the GNU General Public License as published by the Free Software
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Foundation; either version 2 of the License, or (at your option) any
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later version.
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or both in parallel, as here.
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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 General Public License
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for more details.
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You should have received copies of the GNU General Public License and the
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GNU Lesser General Public License along with the GNU MP Library. If not,
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see https://www.gnu.org/licenses/. */
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#include "gmp-impl.h"
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#include "longlong.h"
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/* This uses a plain right-to-left square-and-multiply algorithm.
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FIXME: When popcount(e) is not too small, it would probably speed things up
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to use a k-ary sliding window algorithm. */
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void
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mpf_pow_ui (mpf_ptr r, mpf_srcptr b, unsigned long int e)
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{
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mpf_t t;
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int cnt;
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if (e <= 1)
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{
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if (e == 0)
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mpf_set_ui (r, 1);
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else
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mpf_set (r, b);
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return;
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}
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count_leading_zeros (cnt, (mp_limb_t) e);
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cnt = GMP_LIMB_BITS - 1 - cnt;
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/* Increase computation precision as a function of the exponent. Adding
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log2(popcount(e) + log2(e)) bits should be sufficient, but we add log2(e),
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i.e. much more. With mpf's rounding of precision to whole limbs, this
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will be excessive only when limbs are artificially small. */
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mpf_init2 (t, mpf_get_prec (r) + cnt);
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mpf_set (t, b); /* consume most significant bit */
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while (--cnt > 0)
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{
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mpf_mul (t, t, t);
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if ((e >> cnt) & 1)
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mpf_mul (t, t, b);
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}
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/* Do the last iteration specially in order to save a copy operation. */
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if (e & 1)
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{
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mpf_mul (t, t, t);
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mpf_mul (r, t, b);
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}
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else
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{
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mpf_mul (r, t, t);
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}
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mpf_clear (t);
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}
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