103 lines
2.6 KiB
C
103 lines
2.6 KiB
C
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/*=============================================================================
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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) 2012 Sebastian Pancratz
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Copyright (C) 2013 Mike Hansen
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******************************************************************************/
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#include "ulong_extras.h"
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#include "fq.h"
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/*
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Sets (rop, 2d-1) to the image of (op, len) under the Frobenius operator
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raised to the e-th power, assuming that neither op nor e are zero.
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*/
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void
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_fq_frobenius(fmpz * rop, const fmpz * op, slong len, slong e, 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 (len == 1) /* op is in Fp, not just Fq */
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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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fmpz_t t;
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fmpz_init(t);
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fmpz_pow_ui(t, fq_ctx_prime(ctx), e);
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_fq_pow(rop, op, len, t, ctx);
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fmpz_clear(t);
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}
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}
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void
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fq_frobenius(fq_t rop, const fq_t op, slong e, const fq_ctx_t ctx)
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{
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const slong d = fq_ctx_degree(ctx);
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e = e % d;
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if (e < 0)
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e += d;
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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 (e == 0)
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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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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_frobenius(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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