111 lines
2.9 KiB
C
111 lines
2.9 KiB
C
/* mpz_pow_ui(res, base, exp) -- Set RES to BASE**EXP.
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Copyright (C) 1991 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 General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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The GNU MP Library 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 the GNU MP Library; see the file COPYING. If not, write to
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the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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#ifndef BERKELEY_MP
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void
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#ifdef __STDC__
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mpz_pow_ui (MP_INT *r, const MP_INT *b, unsigned long int e)
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#else
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mpz_pow_ui (r, b, e)
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MP_INT *r;
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const MP_INT *b;
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unsigned long int e;
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#endif
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#else /* BERKELEY_MP */
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void
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#ifdef __STDC__
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rpow (const MP_INT *b, signed short int e, MP_INT *r)
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#else
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rpow (b, e, r)
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const MP_INT *b;
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signed short int e;
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MP_INT *r;
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#endif
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#endif /* BERKELEY_MP */
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{
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mp_ptr rp, bp, tp, xp;
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mp_size rsize, bsize;
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int cnt, i;
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bsize = ABS (b->size);
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/* Single out cases that give result == 0 or 1. These tests are here
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to simplify the general code below, not to optimize. */
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if (bsize == 0
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#ifdef BERKELEY_MP
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|| e < 0
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#endif
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)
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{
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r->size = 0;
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return;
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}
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if (e == 0)
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{
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r->d[0] = 1;
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r->size = 1;
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return;
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}
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/* Count the number of leading zero bits of the base's most
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significant limb. */
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count_leading_zeros (cnt, b->d[bsize - 1]);
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/* Over-estimate space requirements and allocate enough space for the
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final result in two temporary areas. The two areas are used to
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alternately hold the input and recieve the product for mpn_mul.
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(This scheme is used to fulfill the requirements of mpn_mul; that
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the product space may not be the same as any of the input operands.) */
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rsize = bsize * e - cnt * e / BITS_PER_MP_LIMB;
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rp = (mp_ptr) alloca (rsize * BYTES_PER_MP_LIMB);
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tp = (mp_ptr) alloca (rsize * BYTES_PER_MP_LIMB);
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bp = b->d;
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MPN_COPY (rp, bp, bsize);
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rsize = bsize;
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count_leading_zeros (cnt, e);
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for (i = BITS_PER_MP_LIMB - cnt - 2; i >= 0; i--)
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{
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rsize = mpn_mul (tp, rp, rsize, rp, rsize);
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xp = tp; tp = rp; rp = xp;
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if ((e & ((mp_limb) 1 << i)) != 0)
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{
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rsize = mpn_mul (tp, rp, rsize, bp, bsize);
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xp = tp; tp = rp; rp = xp;
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}
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}
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/* Now then we know the exact space requirements, reallocate if
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necessary. */
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if (r->alloc < rsize)
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_mpz_realloc (r, rsize);
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MPN_COPY (r->d, rp, rsize);
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r->size = (e & 1) == 0 || b->size >= 0 ? rsize : -rsize;
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alloca (0);
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}
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