/*

 * Copyright (c) 2003, 2007-14 Matteo Frigo

 * Copyright (c) 2003, 2007-14 Massachusetts Institute of Technology

 *

 * This program 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.

 *

 * This program 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 this program; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA

 *

 */

/* Solve an R2HC/HC2R problem via post/pre processing of a DHT.  This

   is mainly useful because we can use Rader to compute DHTs of prime

   sizes.  It also allows us to express hc2r problems in terms of r2hc

   (via dht-r2hc), and to do hc2r problems without destroying the input. */

#include "rdft/rdft.h"

typedef struct {

     solver super;

} S;

typedef struct {

     plan_rdft super;

     plan *cld;

     INT is, os;

     INT n;

} P;

static void apply_r2hc(const plan *ego_, R *I, R *O)

{

     const P *ego = (const P *) ego_;

     INT os;

     INT i, n;

     {

    plan_rdft *cld = (plan_rdft *) ego->cld;

    cld->apply((plan *) cld, I, O);

     }

     n = ego->n;

     os = ego->os;

     for (i = 1; i < n - i; ++i) {

    E a, b;

    a = K(0.5) * O[os * i];

    b = K(0.5) * O[os * (n - i)];

    O[os * i] = a + b;

#if FFT_SIGN == -1

    O[os * (n - i)] = b - a;

#else

    O[os * (n - i)] = a - b;

#endif

     }

}

/* hc2r, destroying input as usual */

static void apply_hc2r(const plan *ego_, R *I, R *O)

{

     const P *ego = (const P *) ego_;

     INT is = ego->is;

     INT i, n = ego->n;

     for (i = 1; i < n - i; ++i) {

    E a, b;

    a = I[is * i];

    b = I[is * (n - i)];

#if FFT_SIGN == -1

    I[is * i] = a - b;

    I[is * (n - i)] = a + b;

#else

    I[is * i] = a + b;

    I[is * (n - i)] = a - b;

#endif

     }

     {

    plan_rdft *cld = (plan_rdft *) ego->cld;

    cld->apply((plan *) cld, I, O);

     }

}

/* hc2r, without destroying input */

static void apply_hc2r_save(const plan *ego_, R *I, R *O)

{

     const P *ego = (const P *) ego_;

     INT is = ego->is, os = ego->os;

     INT i, n = ego->n;

     O[0] = I[0];

     for (i = 1; i < n - i; ++i) {

    E a, b;

    a = I[is * i];

    b = I[is * (n - i)];

#if FFT_SIGN == -1

    O[os * i] = a - b;

    O[os * (n - i)] = a + b;

#else

    O[os * i] = a + b;

    O[os * (n - i)] = a - b;

#endif

     }

     if (i == n - i)

    O[os * i] = I[is * i];

     {

    plan_rdft *cld = (plan_rdft *) ego->cld;

    cld->apply((plan *) cld, O, O);

     }

}

static void awake(plan *ego_, enum wakefulness wakefulness)

{

     P *ego = (P *) ego_;

     X(plan_awake)(ego->cld, wakefulness);

}

static void destroy(plan *ego_)

{

     P *ego = (P *) ego_;

     X(plan_destroy_internal)(ego->cld);

}

static void print(const plan *ego_, printer *p)

{

     const P *ego = (const P *) ego_;

     p->print(p, "(%s-dht-%D%(%p%))", 

        ego->super.apply == apply_r2hc ? "r2hc" : "hc2r",

        ego->n, ego->cld);

}

static int applicable0(const solver *ego_, const problem *p_)

{

     const problem_rdft *p = (const problem_rdft *) p_;

     UNUSED(ego_);

     return (1

       && p->sz->rnk == 1

       && p->vecsz->rnk == 0

       && (p->kind[0] == R2HC || p->kind[0] == HC2R)

       /* hack: size-2 DHT etc. are defined as being equivalent

    to size-2 R2HC in problem.c, so we need this to prevent

    infinite loops for size 2 in EXHAUSTIVE mode: */

       && p->sz->dims[0].n > 2

    );

}

static int applicable(const solver *ego, const problem *p_, 

          const planner *plnr)

{

     return (!NO_SLOWP(plnr) && applicable0(ego, p_));

}

static plan *mkplan(const solver *ego_, const problem *p_, planner *plnr)

{

     P *pln;

     const problem_rdft *p;

     problem *cldp;

     plan *cld;

     static const plan_adt padt = {

    X(rdft_solve), awake, print, destroy

     };

     if (!applicable(ego_, p_, plnr))

          return (plan *)0;

     p = (const problem_rdft *) p_;

     if (p->kind[0] == R2HC || !NO_DESTROY_INPUTP(plnr))

    cldp = X(mkproblem_rdft_1)(p->sz, p->vecsz, p->I, p->O, DHT);

     else {

    tensor *sz = X(tensor_copy_inplace)(p->sz, INPLACE_OS);

    cldp = X(mkproblem_rdft_1)(sz, p->vecsz, p->O, p->O, DHT);

    X(tensor_destroy)(sz);

     }

     cld = X(mkplan_d)(plnr, cldp);

     if (!cld) return (plan *)0;

     pln = MKPLAN_RDFT(P, &padt, p->kind[0] == R2HC ? 

           apply_r2hc : (NO_DESTROY_INPUTP(plnr) ?

             apply_hc2r_save : apply_hc2r));

     pln->n = p->sz->dims[0].n;

     pln->is = p->sz->dims[0].is;

     pln->os = p->sz->dims[0].os;

     pln->cld = cld;

     pln->super.super.ops = cld->ops;

     pln->super.super.ops.other += 4 * ((pln->n - 1)/2);

     pln->super.super.ops.add += 2 * ((pln->n - 1)/2);

     if (p->kind[0] == R2HC)

    pln->super.super.ops.mul += 2 * ((pln->n - 1)/2);

     if (pln->super.apply == apply_hc2r_save)

    pln->super.super.ops.other += 2 + (pln->n % 2 ? 0 : 2);

     return &(pln->super.super);

}

/* constructor */

static solver *mksolver(void)

{

     static const solver_adt sadt = { PROBLEM_RDFT, mkplan, 0 };

     S *slv = MKSOLVER(S, &sadt);

     return &(slv->super);

}

void X(rdft_dht_register)(planner *p)

{

     REGISTER_SOLVER(p, mksolver());

}