pqc/external/flint-2.4.3/fmpz_poly/hensel_lift_only_inverse.c

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/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011 Andy Novocin
Copyright (C) 2011 Sebastian Pancratz
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_poly.h"
#include "fmpz_mod_poly.h"
/*
Macro for the lift B := [{(1 - aG - bH)/p} * b mod g] p + b,
of length at most lenG - 1.
Assumes that {C, lenC} contains the inner part {(1 - aG - bH)/p} mod p1,
where lenC = max(lenA + lenG - 1, lenB + lenH - 1). Requires temporary
space M, D, E. We really only need
lenM = max(lenG, lenH)
lenE = max(lenG + lenB - 2, lenH + lenA - 2)
lenD = max(lenC, lenE)
Writes {B, lenG - 1}. The cofactor that is lifted is the
polynomial {b, lenB}, which may be aliased with B. Although
it suffices to have g modulo p, there is no harm in supplying
{g, lenG} only reduced modulo p p1.
*/
#define liftinv(B, b, lenB, g, lenG) \
do { \
_fmpz_vec_scalar_mod_fmpz(M, g, lenG, p1); \
_fmpz_mod_poly_rem(D, C, lenC, M, lenG, one, p1); \
_fmpz_mod_poly_mul(E, D, lenG - 1, b, lenB, p1); \
if (lenB > 1) \
{ \
_fmpz_mod_poly_rem(D, E, lenG + lenB - 2, M, lenG, one, p1); \
_fmpz_vec_scalar_mul_fmpz(M, D, lenG - 1, p); \
} \
else \
{ \
_fmpz_vec_scalar_mul_fmpz(M, E, lenG - 1, p); \
} \
_fmpz_poly_add(B, M, lenG - 1, b, lenB); \
} while (0)
void _fmpz_poly_hensel_lift_only_inverse(fmpz *A, fmpz *B,
const fmpz *G, slong lenG, const fmpz *H, slong lenH,
const fmpz *a, slong lenA, const fmpz *b, slong lenB,
const fmpz_t p, const fmpz_t p1)
{
const fmpz one[1] = {WORD(1)};
const slong lenC = FLINT_MAX(lenA + lenG - 1, lenB + lenH - 1);
const slong lenM = FLINT_MAX(lenG, lenH);
const slong lenE = FLINT_MAX(lenG + lenB - 2, lenH + lenA - 2);
const slong lenD = FLINT_MAX(lenC, lenE);
fmpz *C, *D, *E, *M;
C = _fmpz_vec_init(lenC + lenD + lenD + lenM);
D = C + lenC;
E = D + lenD;
M = E + lenE;
if (lenG >= lenA)
_fmpz_poly_mul(C, G, lenG, a, lenA);
else
_fmpz_poly_mul(C, a, lenA, G, lenG);
if (lenH >= lenB)
_fmpz_poly_mul(D, H, lenH, b, lenB);
else
_fmpz_poly_mul(D, b, lenB, H, lenH);
_fmpz_vec_add(C, C, D, lenC);
fmpz_sub_ui(C, C, 1);
_fmpz_vec_neg(C, C, lenC);
_fmpz_vec_scalar_divexact_fmpz(D, C, lenC, p);
_fmpz_vec_scalar_mod_fmpz(C, D, lenC, p1);
liftinv(B, b, lenB, G, lenG);
liftinv(A, a, lenA, H, lenH);
_fmpz_vec_clear(C, lenC + lenD + lenD + lenM);
}
void fmpz_poly_hensel_lift_only_inverse(fmpz_poly_t Aout, fmpz_poly_t Bout,
const fmpz_poly_t G, const fmpz_poly_t H,
const fmpz_poly_t a, const fmpz_poly_t b,
const fmpz_t p, const fmpz_t p1)
{
fmpz_poly_fit_length(Aout, H->length - 1);
fmpz_poly_fit_length(Bout, G->length - 1);
_fmpz_poly_hensel_lift_only_inverse(Aout->coeffs, Bout->coeffs,
G->coeffs, G->length, H->coeffs, H->length,
a->coeffs, a->length, b->coeffs, b->length, p, p1);
_fmpz_poly_set_length(Aout, H->length - 1);
_fmpz_poly_set_length(Bout, G->length - 1);
_fmpz_poly_normalise(Aout);
_fmpz_poly_normalise(Bout);
}