176 lines
4.3 KiB
C
176 lines
4.3 KiB
C
/*=============================================================================
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This file is part of FLINT.
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FLINT 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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FLINT 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 FLINT; 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) 2011, 2012 Sebastian Pancratz
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Copyright (C) 2013 Mike Hansen
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******************************************************************************/
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#include "fq.h"
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void
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_fq_pow(fmpz * rop, const fmpz * op, slong len, const fmpz_t e,
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const fq_ctx_t ctx)
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{
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const slong d = fq_ctx_degree(ctx);
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if (fmpz_is_zero(e))
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{
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fmpz_one(rop);
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_fmpz_vec_zero(rop + 1, 2 * d - 1 - 1);
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}
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else if (fmpz_is_one(e))
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{
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_fmpz_vec_set(rop, op, len);
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_fmpz_vec_zero(rop + len, 2 * d - 1 - len);
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}
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else
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{
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ulong bit;
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fmpz *v = _fmpz_vec_init(2 * d - 1);
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fmpz *R, *S, *T;
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_fmpz_vec_zero(rop, 2 * d - 1);
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/*
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Set bits to the bitmask with a 1 one place lower than the msb of e
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*/
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bit = fmpz_bits(e) - 2;
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/*
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Trial run without any polynomial arithmetic to determine the parity
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of the number of swaps; then set R and S accordingly
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*/
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{
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unsigned int swaps = 0U;
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ulong bit2 = bit;
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if (fmpz_tstbit(e, bit2))
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swaps = ~swaps;
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while (bit2--)
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if (!fmpz_tstbit(e, bit2))
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swaps = ~swaps;
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if (swaps == 0U)
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{
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R = rop;
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S = v;
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}
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else
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{
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R = v;
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S = rop;
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}
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}
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/*
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We unroll the first step of the loop, referring to {op, len}
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*/
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_fmpz_poly_sqr(R, op, len);
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_fq_reduce(R, 2 * len - 1, ctx);
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if (fmpz_tstbit(e, bit))
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{
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_fmpz_poly_mul(S, R, d, op, len);
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_fq_reduce(S, d + len - 1, ctx);
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T = R;
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R = S;
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S = T;
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}
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while (bit--)
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{
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if (fmpz_tstbit(e, bit))
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{
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_fmpz_poly_sqr(S, R, d);
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_fq_reduce(S, 2 * d - 1, ctx);
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_fmpz_poly_mul(R, S, d, op, len);
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_fq_reduce(R, d + len - 1, ctx);
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}
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else
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{
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_fmpz_poly_sqr(S, R, d);
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_fq_reduce(S, 2 * d - 1, ctx);
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T = R;
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R = S;
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S = T;
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}
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}
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_fmpz_vec_clear(v, 2 * d - 1);
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}
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}
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void
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fq_pow(fq_t rop, const fq_t op, const fmpz_t e, const fq_ctx_t ctx)
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{
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if (fmpz_sgn(e) < 0)
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{
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flint_printf("Exception (fq_pow). e < 0.\n");
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abort();
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}
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if (fmpz_is_zero(e))
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{
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fq_one(rop, ctx);
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}
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else if (fq_is_zero(op, ctx))
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{
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fq_zero(rop, ctx);
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}
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else if (fmpz_is_one(e))
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{
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fq_set(rop, op, ctx);
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}
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else
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{
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const slong d = fq_ctx_degree(ctx);
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fmpz *t;
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if (rop == op)
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{
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t = _fmpz_vec_init(2 * d - 1);
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}
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else
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{
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fmpz_poly_fit_length(rop, 2 * d - 1);
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t = rop->coeffs;
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}
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_fq_pow(t, op->coeffs, op->length, e, ctx);
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if (rop == op)
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{
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_fmpz_vec_clear(rop->coeffs, rop->alloc);
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rop->coeffs = t;
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rop->alloc = 2 * d - 1;
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rop->length = d;
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}
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else
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{
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_fmpz_poly_set_length(rop, d);
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}
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_fmpz_poly_normalise(rop);
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}
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}
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