106 lines
3.0 KiB
C
106 lines
3.0 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) 2012 Sebastian Pancratz
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Copyright (C) 2013 Mike Hansen
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******************************************************************************/
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#include "fq_nmod.h"
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#include "nmod_mat.h"
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/*
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Computes the norm on $\mathbf{Q}_q$ to precision $N \geq 1$.
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When $N = 1$, this computes the norm on $\mathbf{F}_q$.
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*/
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void _fq_nmod_norm(fmpz_t rop2, const mp_limb_t *op, slong len,
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const fq_nmod_ctx_t ctx)
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{
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const slong d = fq_nmod_ctx_degree(ctx);
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mp_limb_t rop;
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if (len == 1)
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{
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rop = n_powmod2_ui_preinv(op[0], d, ctx->mod.n, ctx->mod.ninv);
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}
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else
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{
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/* Construct an ad hoc matrix M and set rop to det(M) */
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{
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const slong n = d + len - 1;
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slong i, k;
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nmod_mat_t M;
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nmod_mat_init(M, n, n, ctx->mod.n);
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for (k = 0; k < len-1; k++)
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{
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for (i = 0; i < ctx->len; i++)
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{
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M->entries[k * n + k + (d - ctx->j[i])] = ctx->a[i];
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}
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}
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for (k = 0; k < d; k++)
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{
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for (i = 0; i < len; i++)
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{
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M->entries[(len-1 + k) * n + k + (len-1 - i)] = op[i];
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}
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}
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rop = _nmod_mat_det(M);
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nmod_mat_clear(M);
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}
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/*
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XXX: This part of the code is currently untested as the Conway
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polynomials used for the extension Fq/Fp are monic.
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*/
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if (ctx->a[ctx->len - 1] != WORD(1))
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{
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mp_limb_t f;
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f = n_powmod2_ui_preinv(ctx->a[ctx->len - 1], len - 1, ctx->mod.n, ctx->mod.ninv);
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f = n_invmod(f, ctx->mod.n);
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rop = n_mulmod2_preinv(f, rop, ctx->mod.n, ctx->mod.ninv);
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}
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}
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fmpz_set_ui(rop2, rop);
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}
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void fq_nmod_norm(fmpz_t rop, const fq_nmod_t op, const fq_nmod_ctx_t ctx)
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{
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if (fq_nmod_is_zero(op, ctx))
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{
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fmpz_zero(rop);
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return;
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}
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else
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{
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_fq_nmod_norm(rop, op->coeffs, op->length, ctx);
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}
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}
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