/*=============================================================================

    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) 2013 Mike Hansen

******************************************************************************/

*******************************************************************************

    Context Management

*******************************************************************************

void fq_zech_ctx_init(fq_zech_ctx_t ctx, const fmpz_t p,
                      slong d, const char *var)

    Initialises the context for prime~$p$ and extension degree~$d$,
    with name \code{var} for the generator.  By default, it will try
    use a Conway polynomial; if one is not available, a random
    irreducible polynomial will be used.

    Assumes that $p$ is a prime and $p^d < 2^{FLINT_BITS}$.

    Assumes that the string \code{var} is a null-terminated string
    of length at least one.

int _fq_zech_ctx_init_conway(fq_zech_ctx_t ctx, const fmpz_t p,
                             slong d, const char *var)

    Attempts to initialise the context for prime~$p$ and extension
    degree~$d$, with name \code{var} for the generator using a Conway
    polynomial for the modulus.

    Returns $1$ if the Conway polynomial is in the database for the
    given size and the initialization is successful; otherwise,
    returns $0$.

    Assumes that $p$ is a prime and $p^d < 2^{FLINT_BITS}$.

    Assumes that the string \code{var} is a null-terminated string
    of length at least one.


void fq_zech_ctx_init_conway(fq_zech_ctx_t ctx, const fmpz_t p,
                             slong d, const char *var)

    Initialises the context for prime~$p$ and extension degree~$d$,
    with name \code{var} for the generator using a Conway polynomial
    for the modulus.

    Assumes that $p$ is a prime and $p^d < 2^{FLINT_BITS}$.

    Assumes that the string \code{var} is a null-terminated string
    of length at least one.

void fq_zech_ctx_init_modulus(fq_zech_ctx_t ctx
                              nmod_poly_t modulus,
                              const char *var)

    Initialises the context for given \code{modulus} with name
    \code{var} for the generator.

    Assumes that \code{modulus} is and irreducible polynomial over
    $\mathbf{F}_{p}$.

    Assumes that the string \code{var} is a null-terminated string
    of length at least one.

void fq_zech_ctx_init_fq_nmod_ctx(fq_zech_ctx_t ctx, fq_nmod_ctx_t ctxn);

    Initializes the context \code{ctx} to be the Zech representation
    for the finite field given by \code{ctxn}.

void fq_zech_ctx_clear(fq_zech_ctx_t ctx)

    Clears all memory that has been allocated as part of the context.

long fq_zech_ctx_degree(const fq_zech_ctx_t ctx)

    Returns the degree of the field extension
    $[\mathbf{F}_{q} : \mathbf{F}_{p}]$, which
    is equal to $\log_{p} q$.

fmpz * fq_zech_ctx_prime(const fq_zech_ctx_t ctx)

    Returns a pointer to the prime $p$ in the context.

void fq_zech_ctx_order(fmpz_t f, const fq_zech_ctx_t ctx)

     Sets $f$ to be the size of the finite field.

mp_limb_t fq_zech_ctx_order_ui(const fq_zech_ctx_t ctx)

     Returns the size of the finite field.

int fq_zech_ctx_fprint(FILE * file, const fq_zech_ctx_t ctx)

    Prints the context information to {\tt{file}}. Returns 1 for a
    success and a negative number for an error.

void fq_zech_ctx_print(const fq_zech_ctx_t ctx)

    Prints the context information to {\tt{stdout}}.

void fq_zech_ctx_randtest(fq_zech_ctx_t ctx)

    Initializes \code{ctx} to a random finite field.  Assumes that
    \code{fq_zech_ctx_init} as not been called on \code{ctx} already.

void fq_zech_ctx_randtest_reducible(fq_zech_ctx_t ctx)

    Since the Zech logarithm representation does not work with a
    non-irreducible modulus, does the same as
    \code{fq_zech_ctx_randtest}.

*******************************************************************************

    Memory management

*******************************************************************************

void fq_zech_init(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Initialises the element \code{rop}, setting its value to~$0$.

void fq_zech_init2(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Initialises \code{poly} with at least enough space for it to be an element
    of \code{ctx} and sets it to~$0$.

void fq_zech_clear(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Clears the element \code{rop}.

void _fq_zech_sparse_reduce(mp_ptr R, slong lenR, const fq_zech_ctx_t ctx)

    Reduces \code{(R, lenR)} modulo the polynomial $f$ given by the
    modulus of \code{ctx}.

void _fq_zech_dense_reduce(mp_ptr R, slong lenR, const fq_zech_ctx_t ctx)

    Reduces \code{(R, lenR)} modulo the polynomial $f$ given by the
    modulus of \code{ctx} using Newton division.

void _fq_zech_reduce(mp_ptr r, slong lenR, const fq_zech_ctx_t ctx)

    Reduces \code{(R, lenR)} modulo the polynomial $f$ given by the
    modulus of \code{ctx}.  Does either sparse or dense reduction
    based on \code{ctx->sparse_modulus}.

void fq_zech_reduce(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Reduces the polynomial \code{rop} as an element of
    $\mathbf{F}_p[X] / (f(X))$.

*******************************************************************************

    Basic arithmetic

*******************************************************************************

void fq_zech_add(fq_zech_t rop, const fq_zech_t op1, const fq_zech_t op2,
                 const fq_zech_ctx_t ctx)

    Sets \code{rop} to the sum of \code{op1} and \code{op2}.

void fq_zech_sub(fq_zech_t rop, const fq_zech_t op1, const fq_zech_t op2,
                 const fq_zech_ctx_t ctx)

    Sets \code{rop} to the difference of \code{op1} and \code{op2}.

void fq_zech_sub_one(fq_zech_t rop, const fq_zech_t op1, const fq_zech_ctx_t ctx)

    Sets \code{rop} to the difference of \code{op1} and $1$.

void fq_zech_neg(fq_zech_t rop, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Sets \code{rop} to the negative of \code{op}.

void fq_zech_mul(fq_zech_t rop, const fq_zech_t op1, const fq_zech_t op2,
                 const fq_zech_ctx_t ctx)

    Sets \code{rop} to the product of \code{op1} and \code{op2},
    reducing the output in the given context.

void fq_zech_mul_fmpz(fq_zech_t rop, const fq_zech_t op, const fmpz_t x,
                      const fq_zech_ctx_t ctx)

    Sets \code{rop} to the product of \code{op} and $x$,
    reducing the output in the given context.

void fq_zech_mul_si(fq_zech_t rop, const fq_zech_t op, slong x,
                    const fq_zech_ctx_t ctx)

    Sets \code{rop} to the product of \code{op} and $x$,
    reducing the output in the given context.

void fq_zech_mul_ui(fq_zech_t rop, const fq_zech_t op, ulong x,
                    const fq_zech_ctx_t ctx)

    Sets \code{rop} to the product of \code{op} and $x$,
    reducing the output in the given context.

void fq_zech_sqr(fq_zech_t rop, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Sets \code{rop} to the square of \code{op},
    reducing the output in the given context.

void _fq_zech_inv(mp_ptr *rop, mp_srcptr *op, slong len, const fq_zech_ctx_t ctx)

    Sets \code{(rop, d)} to the inverse of the non-zero element
    \code{(op, len)}.

void fq_zech_inv(fq_zech_t rop, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Sets \code{rop} to the inverse of the non-zero element \code{op}.

void _fq_zech_pow(mp_ptr *rop, mp_srcptr *op, slong len, const fmpz_t e,
                  const fq_zech_ctx_t ctx)

    Sets \code{(rop, 2*d-1)} to \code{(op,len)} raised to the power~$e$,
    reduced modulo $f(X)$, the modulus of \code{ctx}.

    Assumes that $e \geq 0$ and that \code{len} is positive and at most~$d$.

    Although we require that \code{rop} provides space for
    $2d - 1$ coefficients, the output will be reduced modulo
    $f(X)$, which is a polynomial of degree~$d$.

    Does not support aliasing.

void fq_zech_pow(fq_zech_t rop, const fq_zech_t op, const fmpz_t e,
                 const fq_zech_ctx_t ctx)

    Sets \code{rop} the \code{op} raised to the power~$e$.

    Currently assumes that $e \geq 0$.

    Note that for any input \code{op}, \code{rop} is set to~$1$
    whenever $e = 0$.

void fq_zech_pow_ui(fq_zech_t rop, const fq_zech_t op, const ulong e,
                    const fq_zech_ctx_t ctx)

    Sets \code{rop} the \code{op} raised to the power~$e$.

    Currently assumes that $e \geq 0$.

    Note that for any input \code{op}, \code{rop} is set to~$1$
    whenever $e = 0$.

*******************************************************************************

    Roots

*******************************************************************************

void fq_zech_pth_root(fq_zech_t rop, const fq_zech_t op1,
                      const fq_zech_ctx_t ctx)

    Sets \code{rop} to a $p^{th}$ root root of \code{op1}.  Currently,
    this computes the root by raising \code{op1} to $p^{d-1}$ where
    $d$ is the degree of the extension.

*******************************************************************************

    Output

*******************************************************************************

int fq_zech_fprint_pretty(FILE *file, const fq_zech_t op,
                          const fq_zech_ctx_t ctx)

    Prints a pretty representation of \code{op} to \code{file}.

    In the current implementation, always returns~$1$.  The return code is
    part of the function's signature to allow for a later implementation to
    return the number of characters printed or a non-positive error code.

int fq_zech_print_pretty(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Prints a pretty representation of \code{op} to \code{stdout}.

    In the current implementation, always returns~$1$.  The return code is
    part of the function's signature to allow for a later implementation to
    return the number of characters printed or a non-positive error code.

void fq_zech_fprint(FILE * file, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Prints a representation of \code{op} to \code{file}.

void fq_zech_print(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Prints a representation of \code{op} to \code{stdout}.

char * fq_zech_get_str(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Returns the plain FLINT string representation of the element
    \code{op}.

char * fq_zech_get_str_pretty(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Returns a pretty representation of the element~\code{op} using the
    null-terminated string \code{x} as the variable name.

*******************************************************************************

    Randomisation

*******************************************************************************

void fq_zech_randtest(fq_zech_t rop, flint_rand_t state,
                      const fq_zech_ctx_t ctx)

    Generates a random element of $\mathbb{F}_q$.

void fq_zech_randtest_not_zero(fq_zech_t rop, flint_rand_t state,
                             const fq_zech_ctx_t ctx)

    Generates a random non-zero element of $\mathbb{F}_q$.

void fq_zech_randtest_dense(fq_zech_t rop, flint_rand_t state,
                            const fq_zech_ctx_t ctx)

    Generates a random element of $\mathbb{F}_q$ which has an
    underlying polynomial with dense coefficients.

*******************************************************************************

    Assignments and conversions

*******************************************************************************

void fq_zech_set(fq_zech_t rop, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Sets \code{rop} to \code{op}.

void fq_zech_set_ui(fq_zech_t rop, const ulong x, const fq_zech_ctx_t ctx)

    Sets \code{rop} to \code{x}, considered as an element of
    $\mathbb{F}_p$.

void fq_zech_set_fmpz(fq_zech_t rop, const fmpz_t x, const fq_zech_ctx_t ctx)

    Sets \code{rop} to \code{x}, considered as an element of
    $\mathbb{F}_p$.

void fq_zech_swap(fq_zech_t op1, fq_zech_t op2, const fq_zech_ctx_t ctx)

    Swaps the two elements \code{op1} and \code{op2}.

void fq_zech_zero(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Sets \code{rop} to zero.

void fq_zech_one(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Sets \code{rop} to one, reduced in the given context.

void fq_zech_gen(fq_zech_t rop, const fq_zech_ctx_t ctx)

    Sets \code{rop} to a multiplicative generator for the finite field.

void fq_zech_get_fq_nmod(fq_nmod_t rop, const fq_zech_t op,
                         const fq_zech_ctx_t ctx)

    Sets \code{rop} to the \code{fq_nmod_t} element corresponding to
    \code{op}.

void fq_zech_set_fq_nmod(fq_zech_t rop, const fq_nmod_t op,
                         const fq_zech_ctx_t ctx)

    Sets \code{rop} to the \code{fq_zech_t} element corresponding to
    \code{op}.


*******************************************************************************

    Comparison

*******************************************************************************

int fq_zech_is_zero(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Returns whether \code{op} is equal to zero.

int fq_zech_is_one(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Returns whether \code{op} is equal to one.

int fq_zech_equal(const fq_zech_t op1, const fq_zech_t op2,
                  const fq_zech_ctx_t ctx)

    Returns whether \code{op1} and \code{op2} are equal.

int fq_zech_is_invertible(const fq_zech_t op, const fq_zech_ctx_t ctx)

    Returns whether \code{op} is an invertible element.

int fq_zech_is_invertible_f(fq_zech_t f, const fq_zech_t op,
                            const fq_zech_ctx_t ctx)

    Returns whether \code{op} is an invertible element.  If it is not,
    then \code{f} is set of a factor of the modulus.  Since the
    modulus for an \code{fq_zech_ctx_t} is always irreducible, then
    any non-zero \code{op} will be invertible.

*******************************************************************************

    Special functions

*******************************************************************************

void fq_zech_trace(fq_zech_t rop, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Sets \code{rop} to the trace of \code{op}.

    For an element $a \in \mathbb{F}_q$, multiplication by $a$ defines
    a $\mathbb{F}_p$-linear map on $\mathbb{F}_q$.  We define the
    trace of $a$ as the trace of this map.  Equivalently, if $\Sigma$
    generates $\Gal(\mathbb{F}_q / \mathbb{F}_p)$ then the trace of
    $a$ is equal to $\sum_{i=0}^{d-1} \Sigma^i (a)$, where $d =
    \log_{p} q$.

void fq_zech_norm(fq_zech_t rop, const fq_zech_t op, const fq_zech_ctx_t ctx)

    Computes the norm of \code{op}.

    For an element $a \in \mathbb{F}_q$, multiplication by $a$ defines
    a $\mathbb{F}_p$-linear map on $\mathbb{F}_q$.  We define the norm
    of $a$ as the determinant of this map.  Equivalently, if $\Sigma$ generates
    $\Gal(\mathbb{F}_q / \mathbb{F}_p)$ then the trace of $a$ is equal to
    $\prod_{i=0}^{d-1} \Sigma^i (a)$, where
    $d = \text{dim}_{\mathbb{F}_p}(\mathbb{F}_q)$.

    Algorithm selection is automatic depending on the input.

void fq_zech_frobenius(fq_zech_t rop, const fq_zech_t op, slong e,
                       const fq_zech_ctx_t ctx)

    Evaluates the homomorphism $\Sigma^e$ at \code{op}.

    Recall that $\mathbb{F}_q / \mathbb{F}_p$ is Galois with Galois group
    $\langle \sigma \rangle$, which is also isomorphic to
    $\mathbf{Z}/d\mathbf{Z}$, where
    $\sigma \in \Gal(\mathbf{F}_q/\mathbf{F}_p)$ is the Frobenius element
    $\sigma \colon x \mapsto x^p$.

*******************************************************************************

    Bit packing

*******************************************************************************

void fq_zech_bit_pack(fmpz_t f, const fq_zech_t op, mp_bitcnt_t bit_size,
                      const fq_zech_ctx_t ctx)

    Packs \code{op} into bitfields of size \code{bit_size}, writing the
    result to \code{f}.

void fq_zech_bit_unpack(fq_zech_t rop, const fmpz_t f, mp_bitcnt_t bit_size,
                        const fq_zech_ctx_t ctx)

    Unpacks into \code{rop} the element with coefficients packed into
    fields of size \code{bit_size} as represented by the integer
    \code{f}.
